sealing common fluids

8/3/2019 Sealing Common Fluids

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SUBJECT : A new way of classifying chemicals to assure effective sealing 2-12

The most common question asked by seal salesmen is "what are you sealing?" This isusually followed by asking about shaft size, product, temperature, speed, stuffing boxpressure and any other operating conditions they can think of.

The problem with this simplistic approach is that you would have to have a very largedata bank of information to reference a particular problem so as to be able to make asensible seal recommendation. There is a much more logical approach to the problem thatwe will be discussing in the following paragraphs.

A sensible approach to the sealing of various chemicals, mixtures, and compounds wouldbe divided into three parts:

You must know how to select mechanical seal components that will not corrodeor be attacked in any way by the fluid you are sealing, or any other chemicals that

might come into contact with the seal as a result of cleaning the system, flushingthe stuffing box, using barrier fluids between double seals, quenching behind theseal etc..

You must understand the total range of operating conditions of the equipment andthen select seal designs that can handle this range.

You need a method of classifying chemicals that puts them into neat, logicalcategories that can be handled by the use of a special seal design and/orenvironmental controls. It is important to note that the sealing environment willaffect the sealing fluid often preventing the lapped sealing faces from staying incontact..

In this paper we will concentrate on the classification of chemicals and leave the selectionof seal materials, types of seals and use of various environmental controls to other paperson this site

A fluid can be classified as either a liquid or a gas, and can be divided into sevencategorizes:

1. Fluids sensitive to changes in temperature and/or pressure.

2. Fluids that require two mechanical seals.

3. Non lubricating liquids, gases and solids.

4. Slurries, classified as solids in liquid . The solids may or may not beabrasive.

5. Liquids sensitive to agitation.

6. Liquids that react with each other to form a solid.


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7. Lubricating liquids.

We will be investigating each of these categories in detail and learn how they affect thelife of a mechanical seal. In other papers on this site we will learn the detailed methods ofsealing each of these problems

Fluids that are sensitive to changes in temperature and/or pressure.

Corrosive liquids - Most corrosives will double their corrosion rate with a 18degree Fahrenheit (10 C.) rise in temperature. The temperature at the seal face isalways hotter than the temperature recorded in the stuffing box or seal chamber.Keep in mind that any contact between the rotating shaft and a stationarycomponent will cause high heat and will be detected as localized corrosion. Wearrings and throttle bushings are subject to this rubbing. If the equipment isprovided with a cooling jacket. and it is not being utilized, the air inside can act asan insulation increasing the heat in the stuffing box considerably.

Liquids that vaporize - Most any liquid will vaporize if it becomes hot enough, orif the stuffing box pressure gets too low. It is the product with a low specificgravity that give us the most trouble. If the product vaporizes between the lappedseal faces it will separate the faces as the gases expand. When hot water vaporizesit leaves behind any chemicals that were dissolved in the water. Most of thesechemicals are left in a hard crystal form that will damage the lapped faces.

Fluids such as benzene and others with a low specific gravity, will freeze as theyvaporize. If any oil or lubricant was placed on the seal face it will freeze andpossibly damage the lapped faces. Moisture on the outboard side of the seal willfreeze also and restrict movement of the sliding or flexing seal components

Liquids that solidify - Some solidify with an increase in temperature, others with a

decrease. Solvents vaporize with lower pressure leaving any solids behind. Paintis a good example of a product where the solvent will vaporize at or belowatmospheric pressure. In most cases you can reference a vapor pressure chart tolearn when the solvent or carrier will vaporize in your application.

Viscous Products - Their viscosity usually decreases with an increase intemperature and increases with a decrease in temperature. Oil is a good exampleof this type of fluid. High viscosity can interfere with free seal movement andcause seal face contact problems. Lowering the viscosity can often increase theseal face wear as there is not enough film thickness to keep the surfaces separated.You need a film thickness of at least one micron to keep the lapped seal facesseparated.

Film building liquids - Petroleum products will form a varnish when first heatedand then gradually form a layer of coke as the temperature is elevated. Thesetransformations are not reversible and the resultant hard film restricts slidingand/or flexing of the seal components. Hard water is another example of a filmbuilding fluid.

Hot water systems pick up magnetite (Ferric Oxide) from the inside of the pipes.It is black or reddish in color and will be attracted by a magnet. This abrasivematerial will collect on the seal components and destroy the dynamic O-Ring as


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well as restrict the movement of the seal causing the lapped faces to open.Magnetite is a severe problem in new , hot water systems. The problem willlessen as the system ages and the protective film stabilizes.

Liquids that crystallize - Sugar and salt solutions are two examples of these fluids.If the crystals form between the faces they can destroy the carbon. If they form in

the sliding or flexing components they will open the seal faces as the shaft moves.Any leakage across the seal faces will form a solids build up on the other side ofthe seal causing interference as the seal tries to move when it compensates forwear.

The names of these chemicals is not important. If you knew how to seal any oneof them you could seal all of them. It is just a matter of fitting the particularchemical into the right categories and learning how to seal that category.Common sense would dictate that the product temperature and/or pressure mustbe controlled in the seal area to prevent any of the above from occurring. In mostcases you should try to avoid the use of two hard faces in these applications

because of the additional heat that will be generated between the faces. Needlessto say, only hydraulically balanced seals are acceptable in any temperature/pressure sensitive fluid.

Liquids that require two mechanical seals : These seals are installed with a circulatingbarrier fluid that can be a "forced circulation", or in many cases a convection system witha "pumping ring". The pressure of the barrier or buffer fluid can be regulated to indicate afailure in either of the mechanical seals allowing time for a pump shut down, isolationand no subsequent loss in the pumping fluid.

Costly products - Some times the product costs so much you just cannot afford to

have it leak. There are plenty of charts to show how much leakage you get fromvarious sized drips or steady streams. The smallest steady stream you can producewill be between twenty five and thirty U.S. gallons per day (95 to 115 liters/day)

Dangerous products - these fluids are given a special category because even smallamounts of leakage are not acceptable. The danger could fall into manycategories: radiation, toxic, fire, explosion, bacteria, etc.. The new United States'"right to know law" is having a major affect on how mechanical seals used inthese type of products will be repaired.

Pollutants - Usually there is a "penalty" involved and the bad publicity does noone any good. In this day and age a responsible company will not let pollutantsleak to the atmosphere or to the earth for any reason. Fugitive emission legislationhas increased the need for these type of mechanical seals.

Any time an unexpected seal failure would be inconvenient - Down time can be avery costly time in many plants. Two seals prevents the unexpected seal failureshut down. This is especially important with batch operations or when there is noback up pump installed. On the atomic submarine NAUTILUS the back up shaftseal allowed us to get to the surface if a main shaft seal failed while we weresubmerged.


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Sealing non lubricants.

Dry solids - They can clog the sliding components and provide no lubrication forseal faces. Once the faces are open they penetrate between the faces and usuallydestroy the lapped surfaces. Pharmaceuticals, freeze dried coffee and cake mix are

examples of this category. You can think of many more. Non lubricating fluids such as solvents and hot water. We experience more rapid

face wear with these types of fluids. In most cases their film thickness is less thanone micron and cannot support a load between two sliding surfaces

Dry gases- unlike non lubricating liquids they will not conduct heat very well andoften are dangerous at the same time. This is a common problem if you forget tovent the stuffing box of a vertical pump. A top entering mixer is another exampleof this type of application.

Slurries, especially abrasive slurries. Clog the seal components and destroy faces like thedry solids mentioned above.

The list of these products is without end. A slurry is defined as solids in liquidthat cannot be dissolved by normal control of the temperature or pressure. Thenumber of solids or their size is not important. They will collect on or in thesliding or flexing components of the seal causing the faces to open and thenpenetrate between the lapped faces causing leakage and damage. In some designsthe springs or bellows (metallic or elastomer) will experience severe wear in ashort period of time. In these designs it is important to rotate the fluid rather thanhave the bellows component rotate within the abrasive slurry.

Liquids sensitive to agitation :

Dilatants - Their viscosity increases with agitation. This is how cream becomesbutter. Some clay slurries have the same problem. The resulting high viscositieswill restrict the free movement of the seal. When dealing with dilatants it isimportant that you do not continually rotate the fluid in the stuffing box area.

Thixotropic fluids lower their viscosity with agitation. They seldom present aproblem for mechanical seals except for an increase in seal face wear.

Plastic fluids change their viscosity suddenly. Catsup is a good example of thistype of fluid.

Newtonian fluids do not change viscosity with agitation. They present no problemfor mechanical seals.

Liquids that combine together to form a solid.

Epoxy is a combination of a Resin and a hardener. Styrofoam is formed by combining several liquids together.

We seldom have problems with these liquids in pumps because the blending takes placeoutside of the pump, but the problem sometimes comes up in mixer applications. You


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will note that I have not included anaerobic fluids (they solidify in the absence of air) inany of the categories (super glue is the product that first comes to mind).

lubricating liquids

This is the ideal application for a mechanical seal but we seldom see it. Moreoften than not we are sealing raw product that falls into one or more of the abovecategories. Back in the days when we were using packing in pumps we did notpay too much attention to these categories because we were either prepared to letthe product leak on the ground or we would flush in clean liquid and concentrateon sealing the clean flush instead.

Now that leakage is no longer tolerable and product dilution is no longer desirable youmust have knowledge of these categories to approach the job of effective sealing. In mostcases the fluid you are sealing will fall into several of the above mentioned categories.Using Heat transfer oil as an example we note that it falls into the following :

Hot - Normally pumped at 600 -700 Fahrenheit ( 315 -370 C.) the fluid is too hotfor available elastomers.

Film Building - The product "cokes" at these temperatures. Dangerous - You do not need this temperature oil leaking out. It is not only a fire

hazard, but a personnel hazard as well. Recent information indicates that some ofthese oils are also carcinogenic.

Costly - Most of these transfer oils cost between $12.00 to $20.00 per gallon (3,8Ltrs.)

Slurry - Because of the coking, solids are always present.

To successfully seal heat transfer oil you would have to address all of these problems atthe same time. As is the case with all slurry applications, you would also have torecognize the problems with vibration (impeller imbalance), thermal growth, and frequentimpeller adjustments.

In addition to handling various chemicals we are often faced with extreme or severeoperating conditions. These conditions would include:

Hot products - Defined as too hot for one of the seal components, or hot enoughto cause the fluid to change form. Heat transfer oil is a good example of a fluidthat will "coke" at elevated temperature.

Cryogenic fluids - They present a problem for elastomers and some carbon faces.Liquid Nitrogen or Oxygen would be an example. High Pressure - Defined as stuffing box, (not discharge) pressure in excess of 400

psi. (28 bar). Pipe line and boiler circulating pumps can have stuffing boxpressures of this magnitude.

Hard Vacuum - Defined as 10-2 Torr or below. This number is well below mostcondenser or evaporator applications, but does come up every once in a while.


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High Speed - Defined as the seal faces moving greater than 5000 Feet Per Minuteor 25 meters per second. Most process pumps do not approach this speed. TheSundstrand "Sundyne" pump is typical of a high speed application.

Excessive motion - defined as more than 0.005 inches (0,15 mm.) in a radial oraxial direction. Mixers, agitators and specialized equipment have shaft

movements up to 1/8 inch (3 mm). Long shaft vertical pumps and pumpsequipped with sleeve or babbitt bearings, are another application for excessivemotion.

Excessive vibration - Unfortunately there are no reliable numbers for the vibrationlimits of mechanical seals. Most vibration studies have addressed the bearings. Itis important to consider that excessive vibration can:

o Open the lapped seal faces.

o Chip the outside diameter of the carbon face.

o Break the metal bellows used in some seal designs.

o Wear the driving mechanism used to transmit torque from the set screws

to the seal faces.

o Loosen drive screws.o Shorten bearing life

o Most seal designs can damage (frett) expensive sleeves and shafts.

o Some, but not all designs have built in vibration dampers to relieve some

of these problems.

In other papers on this site you can learn how to seal each of these fluid categories andlearn how to protect the mechanical seal against the affects of these extreme operatingconditions.

Link to Mc Nally home page
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SUBJECT : Let's clear up the confusion about flushing seals 3-6

Consumers use the term "flushing" to describe six different methods of bringing fluid tothe stuffing box area of a centrifugal pump. Experienced seal people use different termsto differentiate between the methods.

DISCHARGE RECIRCULATION

A line is connected between the discharge of the pump and the stuffing box. The highpressure fluid is then recirculated through the stuffing box to the back of the impeller andeventually to the pump discharge. This technique presents several problems formaintenance people:

If the fluid contains solids ( and most of them do) the centrifugal action of theimpeller will concentrate the solids on the inside diameter of the pump volute andit is this dirty fluid that is being recirculated to the stuffing box. Needless to say

this will not be good for the mechanical seal because the solid particles will act asa "sand blaster" cutting into the lapped seal faces and clogging the sliding sealcomponents.

The pump wear rings, critical tolerances and close fitting bushings will experiencerapid wear as the solids pass through the narrow clearances.

The only legitimate use of this technique is to pressurize the stuffing box to prevent aliquid from vaporizing. Be careful if you use this method in hot water applicationsespecially if a heat exchanger is installed in the recirculation line. A high temperaturewater or steam leak in any of the fittings could be dangerous for any personnel in the areaand the solids can clog up the heat exchanger.

When this line is used to pressurize the stuffing box you should keep several additionalthings in mind:

Install a close fitting bushing in the bottom of the stuffing box. It will look likethe thermal bushing described in the above illustration. The clearance should be .002 inches/ inch (0,002 mm/mm) of shaft diameter.

Be sure to direct the line away from the lapped seal faces and the thin metal platesif you use a metal bellows seal.

If you are using properly installed , balanced O-ring seals (and you should be),The sealed product will not flash between the faces as long as the stuffing box

pressure is a least one atmosphere higher than the liquid vapor pressure. Thedischarge recirculation line should guarantee you will have this pressuredifference.

SUCTION RECIRCULATION

A line is connected between the suction of the pump and the bottom of the stuffing box orseal gland connection. Many pumps have a connection already tapped at the suction


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throat of the pump for a suction gage, but if none is available you can install one in thepiping or a pipe flange if the piping is not thick enough to be drilled and tapped.

Stuffing box pressure is almost always higher than the suction pressure of the pump.Liquid from behind the impeller will be circulated through the stuffing box to the pump

suction. This liquid has been centrifuged by the impeller and the result is that the liquid inthe stuffing box is considerably cleaner than what you are pumping. In many cases youcan eliminate the need for bringing in clean liquid and diluting your product.

This environment control works very well in closed impeller pump designs and thoseopen impeller designs that adjust towards the pump volute rather than the back plate,such as the Duriron pump.

FLUSHING

A clean liquid, from an outside source is brought into the stuffing box through a

regulating valve at one atmosphere (15 psi. /1 bar) higher than stuffing box pressure. Theliquid should be brought in at the bottom of the stuffing box to insure thorough cleaning.All of this liquid will eventually go into your product.

If you are using balanced O-ring seals you will only need enough liquid to remove solidsthat might interfere with the seal movement. You will not need additional liquid toprovide cooling because balanced seals do not generate enough heat to cause problems inmost applications.

Seal designs that have the springs out of the fluid require only one to two gallons perhour (4 to 8 Ltrs./ hour) of flush. NOTE: this is per hour, not per minute. If you are using

designs with multiple springs in the fluid check with your manufacturer for hisrecommendations. The clean flush can come from several sources:

Clean water A compatible fluid A solvent One of the ingredients in the product Finished product will never hurt raw product. Finished product is almost always

clean. An additive that is going to be put into the product down stream and can be added

at the pump stuffing box instead.

If you are using shop water as the flush you must be careful or solids in the flushingwater will clog up the flow control valve. The shop water pressure also tends to varythrough out the day and in some instances it can fall below the pump stuffing boxpressure. Most states require an air gap in the line if you want to use shop or city water asa flushing medium. A back flow presenter valve is used many times but it is illegal inmost states.


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BARRIER OR BUFFER FLUID

Any time you use two seals in an application you will need a fluid between them. If thefluid between the seals is higher than stuffing box pressure we call it barrier fluid. If it islower than stuffing box pressure we call it buffer fluid The liquid can be circulated eitherby forced circulation, a pumping ring or convection. The method that you will use will bedictated by the pressure, pump speed and shaft size. All seal manufacturers have chartsavailable to give you the correct guidelines.

If you elect to use a forced circulation system be sure to introduce the fluid into thebottom connection and out the top connection. This arrangement will insure that thespace between the seals is vented and proper cooling will take place.

Forced circulation is the recommended method with all vertical shaft applications,although it is possible to offset the centering of the seal gland and get a small amount ofpumping action as the liquid circulating in the seal changes its velocity at the convectiontank connections. Check with your local distributor for an explanation of this principle.

Many of the latest seal designs utilize a built in pumping ring to enhance convection. Thispumping arrangement is very necessary when ever oil is used as the barrier fluid. The

following illustration shows a typical convection system that can be used with twobalanced seals.

Water is one of the best barrier or buffer fluids because of its high specific heat and goodconductivity. Petroleum oil is probably one of the worse because of its low specific heatand poor conductivity. Keep this in mind when you select a barrier or buffer fluid foryour seals.

The type of seal you select will determine if the barrier fluid has to be kept higher orlower than the stuffing box pressure. Fluctuating pressures are normal in this business so


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you should select seals that balance in both directions to eliminate any problems thatmight be caused when the barrier fluid or system pressure varies.

Be sure to connect the convection tank or forced lubrication system so that the inlet is atthe bottom of the double seal and the outlet discharges from the top of the seal. This

arrangement will allow the seal to vent, and insure that the passages are full of liquid.

JACKETING FLUID (B)

High temperature pumps have a cooling/ heating jacket installed around the pumpstuffing box. If a jacket has not been installed on your pump it can be purchased from the

pump manufacturer or an "after market" supplier.

The secret to using a jacketed stuffing box is to install a thermal bushing into the bottomof the stuffing box and then "dead end" the stuffing box liquid. Dead ending means thatno suction or discharge recirculation lines should be installed. Any material that has poorthermal conducting properties will be satisfactory for the bushing provided it iscompatible with what you are sealing. Carbon is an excellent choice because unlikeTeflon it does not change dimensions too much with a change in temperature.

A small amount of liquid or steam through the jacket can control the stuffing box to whatever temperature range you need. In some instances cool heat transfer oil is utilized. Keep

in mind that this jacket is also providing cooling to the bearing case as well as thestuffing box.

Be sure the jacketing fluid is free from calcium (hard water) or any substance that canbuild a film on the inside of the jacket surface and restrict the heat transfer. A number ofcleaners are available if you experience this problem. Condensate is a good jacketingfluid that presents few problems and is usually available.

QUENCHING - Often called vent and drain (Q connection on an A.P.I. gland)

Some seal glands have a vent or quench connection provided behind the seal sothat steam or some other fluid can be used to control temperature in the seal area.


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To shift the load to the outboard seal when sealing a non lubricant with theinboard seal.

This is the normal method of sealing a gas.

JACKETING FLUID

The best method of controlling temperature in the stuffing box when the pump isshut down. Be sure to install the thermal bushing or it will not work very well.

Make sure that there are no suction or discharge recirculation lines connected.

QUENCHING OR VENT & DRAIN - plus the disaster bushing.

The disaster bushing will protect the seal from hitting the inside of the stuffingbox if you have a bearing failure. This is a very important feature in thoseapplications where the product will burn or explode if overheated.

The disaster bushing will protect personnel if there is a massive seal failure. The

majority of the leakage can be directed, down the drain connection, to a collectingtank or vent. To wash away solids from the outboard side of the seal that will prevent "hang

up" as the seal face wears and the seal moves forward. To wash away toxic or corrosive vapors that might leak across the seal faces. To control the temperature in the seal area. As a back up to a heating/ cooling jacketing failure.

The rest of the world calls all of these techniques "FLUSHING". Try to acquire the habitof using the proper terminology so that you will avoid confusion when you communicatewith seal people and your fellow workers.

Link to Mc Nally home page
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SUBJECT: Controlling the pressure in the stuffing box area 4-10

We have very little control over the products that we must seal, but we have a great dealof control over how we elect to seal them. Special seals are seldom the answer. In mostcases satisfactory seal life can be obtained by carefully choosing the seal materials for

temperature and chemical compatibility, selecting a balanced O- ring seal design and thencontrolling the environment in the stuffing box to prevent a change in the fluidcharacteristics from affecting the seal performance.

Controlling stuffing box pressure is one of these controls and is extremely important inmany seal applications. In the following paragraphs we will discuss several methods ofcontrolling pressure but first we will learn where the environmental control is necessary.

We can raise the pressure in the stuffing box to :

Prevent a fluid from vaporizing in the stuffing box or across the seal faces. If the

product vaporizes across the seal faces it can open the faces and possibly do somedamage as the faces rapidly open and close. In many cases solids will be leftbetween the faces as the fluid vaporizes.

To destroy a vacuum in the stuffing box. A balanced O-ring seal can seal eithervacuum or a positive pressure. Vacuum often implies higher heat at the seal facesand that is never good for a mechanical seal.

Most split seal designs can accommodate either vacuum or a positive pressureapplication, but not one that alternates between them ( the reverse pressure isforcing the splits open). Raising the stuffing box pressure will keep it positive sothat a split seal can be applied.

We can raise the pressure between two seals to :

Stop a pressure differential across a dynamic elastomer from failing the elastomer.This is a serious problem when we seal ethylene oxide or any fluid capable ofpenetrating the elastomer and blowing out on the low pressure side.

To prevent sub micron solids from penetrating between the lapped faces. Kaolineis a good example of this type of product. Sub micron products have no problempenetrating lapped seal faces when the pressure drop is from the outside diameterto the inside diameter of the seal face.

To take the load off the inboard face that is sealing a non lubricating fluid andtransfer the load to the outboard seal. This can make a dramatic difference in the

life of the inboard seal To prevent a pressure drop across the faces that could cause a product to solidify.

Many solids are dissolved in a liquid that will vaporize at atmospheric pressure.Paint is a good example of this application.

To prevent a liquid from vaporizing between the inboard faces and blowing themopen.

We can lower the pressure in the stuffing box :


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If it is too high for a standard balanced O-ring seal To vent the air from a vertical pump.

Now to the actual techniques :

Discharge recirculation.

In this application we connect a recirculation line from the discharge side of the pump tothe stuffing box or a flush connection in the gland. You should install a close fittingbushing into the bottom of the stuffing box with a clearance of .002 inch/ inch (0.002mm/mm) of shaft diameter. The bushing can be manufactured from any compatiblematerial with the fluid you are sealing. Carbon is often selected as a first choice.

A properly installed balanced O-ring seal will not generate enough heat to flash a liquidbetween the seal faces as long as the stuffing box pressure is at least one atmosphere (onebar or 15 psi.) higher than the product vapor point. You should have no problem in

getting this additional pressure if you have installed the restriction bushing.

Suction recirculation

The technique is the same as discharge recirculation, but in this application we connectthe stuffing box or seal gland to the suction side of the pump or a low pressure sumpinstead. We do not use a restriction bushing in this application because the differentialpressure can cause the bushing to move and contact the mechanical seal. Suctionrecirculation works best with the proper gland connection but it can be used with thelantern ring connection if necessary. Be sure the connection is on the bottom or as closeto the bottom as possible of the stuffing box or gland.

Caution: Lowering the pressure in the stuffing box is sometimes a bad idea because of thedanger of flashing the sealing fluid. The technique is commonly used, however, toremove air that might be trapped in the stuffing box of a vertical pump or to providenormal circulation through the stuffing box when the sealing fluid contains solids. Byconnecting to the suction side you will be pulling fluid from behind the impeller, throughthe stuffing box and then to the lower pressure on the suction side of the pump. Fluidbehind the impeller usually contains less solids than fluid coming from the pumpdischarge side. It should be mentioned that this technique works very well on most closedimpeller pumps and those open impeller designs that adjust to the volute of the pump.Open impeller designs that adjust to the back plate and double ended, single impeller

designs have the stuffing box pressure just about at suction pressure so this applicationdoes not work very well. We go to larger diameter stuffing boxes in those applications.

Another common application for this technique is to cross connect the stuffing boxes of amulti stage pump to equalize the pressures and balance the seal face wear.

Using two or more seals with a lower pressure between them.


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Some seal companies use this as a technique to stage the pressure in a high pressureapplication. I do not approve of this method because the operator is lead to believe thatthere are multiple seals in the pump when in fact the multiple seals are acting as one anda failure in any one of the seals will fail them all. I believe you would be better offpurchasing a high pressure seal for this application.

Using two seals with a convection tank installed between them.

This is done to take the load off the seal that is sealing a non lubricant or to prevent apressure drop across the seal faces. The convection tank is filled with a lubricating liquidand the pressure is adjusted to provide the necessary pressure differential. With theproper instrumentation you will be able to tell which seal wears out or fails first. Thesecond seal will act as a back up until you can shut the valves and start the repair.

As an example : In the pump stuffing box you have a 75 psi.(5 bar) non lubricatingliquid. You cannot afford product dilution so you install two seals with a lubricating

buffer fluid of 75 psi. (5 bar) between them. This will take the load off of the inboard sealthat is sealing the non lubricant and shift the load to the outer seal that is containing thelubricating barrier fluid.

The convection tank can be purchased or manufactured from an appropriate corrosionresistant material. Some companies (Coca Cola as an example) ship their product in asimilar tank and then scrap the tank because of sanitary or safety regulations. Many ofthese tanks can be purchased at a low price and modified for your needs. The airconnection on the top will allow you to pressurize the tank to the correct pressure foryour application.

Keep in mind that convection tank applications are limited by the combination of sealsize, face combination, barrier fluid pressure and shaft speed. Check with your sealsupplier for a specific recommendation.

When ever possible avoid selecting petroleum base liquids for the barrier fluid circulatingin the tank and between the two seals. Petroleum fluids have a very low specific heat thatwill cause overheating and "coking" problems. If you have the choice. Water is the idealheat barrier fluid because of its conductivity and high specific heat number. If water isnot acceptable choose any compatible fluid with a high conductivity and high specificheat value.


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SUBJECT: Controlling the temperature in the stuffing box area 4-6

Many fluids are adversely affected by a change in their temperature, and when thisreaction takes place seal failure is almost sure to follow. The reaction can take severalforms:

One of the seal components can be destroyed. The elastomer, seal faces, or metalparts will almost always be altered at some degree of change in ambienttemperature.

Coated hard faces can "heat check" (crack). Carbon fillers can melt and pits can form in carbon/ graphite faces as trapped air

expands and blows out pieces of the carbon. Hydrocarbons can solidify (coke) between the seal faces and pull out pieces of

carbon also, causing small pits that will prevent you from conforming to fugitiveemission standards.

Carbon graphite faces can lose their lubricating ability at cryogenic temperature

and chip on the outside diameter as "slip stick" vibration takes place. Elastomers can take a "compression set" and crack at elevated temperature Cold temperatures can cause elastomers to harden. The liquid can crystallize restricting seal movement and opening the faces. The liquid can vaporize between the faces causing them to open. The viscosity of the fluid can change either restricting seal movement or making

the fluid less of a lubricant. The liquid can solidify causing the seal to become inoperative. The liquid's corrosion rate will double with an 18 Fahrenheit (10 C) rise in

temperature. The liquid can convert to a film between the sliding seal components, restricting

their movements. The magnetite that forms in hot water is a good example of this. A film can form on the seal faces causing them to separate. Lapped seal faces can distort and go out of flat at elevated or cryogenic

temperatures.

By keeping the stuffing box temperature within specified limits you can prevent all of theabove from happening. These limits vary with each fluid, but they can be obtained fromany one knowledgeable about the fluid that has to be sealed.

A balanced mechanical seal incorporating the following features and installed at theproper compression, is your best insurance against a significant rise in stuffing boxtemperature:

Proper face balance. 70/ 30 is the most common to 5000 fpm. (25 Meters per sec.) Low friction face materials. Carbon/ graphite vs. a hard face is the best. The correct spring compression to control face loading. Faces with good heat conductivity. Tungsten carbide and silicone carbide have

excellent thermal conductivity compared to most other hard face materials.


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A small cross section carbon/ graphite face press fit into a metal holder is betterthan solid carbon/ graphite for removing heat from between the seal faces.

Sometimes, however, that is not good enough, so occasionally you will have to come upwith some additional method of controlling the temperature in the stuffing box area and

between the lapped seal faces.

THE HEATING / COOLING JACKET.

If your pump does not have a heating/ cooling jacket installed one is usually availablefrom the pump distributor. If possible try to select an oversized stuffing box with a

cooling/ heating jacket cast around it. This jacket can be used to heat a product, cool aproduct, or keep the product within close temperature limits. When using the jacket thereare several important things to keep in mind:

Install a carbon bushing into the bottom of the stuffing box to act as a thermalbarrier. The clearance over the shaft should be about 0.002" per inch diameter ofshaft (0,002 mm/ mm of shaft diameter). The length should be at least 3/8 inch(10 mm).

Dead end the stuffing box. In other words no discharge, flush or suctionrecirculation lines connected to the stuffing box. Many hot fluids contain lots ofsolids; the dead ending feature will allow you to centrifuge the fluid and clean it

up. If you elect to use water as the jacketing fluid make sure that it is not hard water

as it will form a layer of calcium on the walls of the jacket restricting the heattransfer.

This jacket is also used to cool the rotating shaft in hot applications. If the coolingis lost the heat will conduct back to the bearings causing their premature failure.

Steam is an excellent medium to control heating or cooling. A regulating valvecan be installed on the discharge side of the jacket for precision pressure controlwhich will, in turn, control the stuffing box temperature within narrow limits. Amixing valve proportioning steam and water is another method of controllingtemperature within precise limits.

THE QUENCH OR DRAIN CONNECTION


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Quench and drain connections are available in American Petroleum Institute (API ) typeglands. The quench and drain connection (Q) is used in conjunction with a close fitting,non sparking disaster bushing (DB)

When using the quench for temperature control keep in mind:o Excessive fluid will be directed towards the bearing case. Be sure to use

only small amounts of steam or water. It would be wise to replace theexisting grease seals with mechanical bearing seals if you elect to usequench as your primary temperature control method.

o The drain connection should be connected to a suitable tank to save thecondensed steam.

o The quench connection can be used to vent a volatile product to a flare

where it can be burned.o The quench fluid can also remove any solids that have built up outboard of

the seal as well as remove any vapors that might leak across the seal faces.This is an important feature when sealing products that can crystallize atthe seal faces and on the outboard side of the seal.

o The drain connection is used to direct the major amount of failed seal

leakage away from the bearings or any personnel in the area. It should beconnected to an appropriate tank for retention.

THE FLUSH CONNECTION

In temperature control applications we flush in cooled product to control the stuffing boxtemperature. If you use the pump fluid cooled, or cooled finished product you will haveno problem with product dilution.

THE DUAL SEAL

Another method of providing temperature control is to utilize two seals with the correcttemperature liquid circulating between them as a barrier or buffer fluid. Look at the

following illustration:


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When using a dual seal for heating/ cooling be sure to bring the fluid into thebottom of the seal gland and out the top of the gland to insure that the voidbetween the seals is full of fluid. This is an excellent method of controlling thetemperature at the seal faces if you are experiencing an over heating problem.

In many instances a convection tank can be installed between the seals but it willseldom do an adequate job of lowering or raising the barrier fluid temperature. Inalmost every instance forced circulation will be necessary if you need any degreeof heating or cooling. Convection tanks are satisfactory for removing the heatgenerated by balanced seal faces, but that is about all.

In some instances a convection tank has been used with an installed cooling coiland a pumping ring built into the mechanical seal.

The amount of barrier fluid circulation needed will be determined by the seal size,speed, and stuffing box pressure. Your seal supplier will gladly supply thisinformation.

Water should be selected for the barrier fluid when ever possible. Oil is a poorchoice because of its low specific heat and poor conductivity.

THE HEAT EXCHANGER

The normal procedure is to install the heat exchanger in the discharge recirculation line

connected between the pump discharge and the stuffing box. If you elect to use thismethod be careful of the following:

This can be dangerous in hot water applications because a leak in any of thefittings will direct high pressure, hot water into the atmosphere and some one maybe standing close by and become injured.

Many hot fluids also contain solids that will clog up the heat exchanger. The temperature control is effective only while the pump is running. Many seal

failures occur at start up because of lack of proper temperature control while thepump was idle.

If you want to use this method, and only a small amount of cooling is necessary, a

commercial automotive, automatic transmission cooler can be used effectively inmany applications.

A heat exchanger can be used with a pumping ring. In this application lowpressure fluid is circulated out of the top of the stuffing box, to the heatexchanger, and then back to the seal through the bottom connection on the sealgland.

OTHER CONSIDERATIONS


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Vertical pumps require venting or the seal will trap air in the stuffing box, causinghigh heat at the seal faces. To vent the stuffing box properly, connect a suctionrecirculation line between the seal flush connection and the pump suction.Vertical pump applications also present a problem for dual seal applications. Youwill need to provide some method of venting air trapped at the outside seal.

Carbon/ metal composites are a good choice for heat dissipation across the carbonseal face. Try to avoid seal faces that are thermally isolated by elastomers. Silicone carbide is a good choice for the hard face because of its excellent thermal

conductivity feature. Use the alpha sintered type to avoid chemical compatibilityproblems

If you elect to use anti freeze as a barrier fluid between two seals, do not use theautomotive brands as many of them contain an anti leak chemical that will clog upthe mechanical seal. Water is the best barrier fluid because of its high specificheat (1.0) and good conductivity. Oil is a bad choice because of its low specificheat (0.25/0.30), but if you must use it, try to select a heat transfer oil.

Heat pipes should have application in stuffing box cooling, but their applicationexperience is very limited. Try to select seal designs that have the elastomer positioned away from the seal

faces. The elastomer is the one seal component that is very sensitive totemperature change. Because elastomers usually have poor thermal conductivity,cooling one side of the elastomer has a minimal affect on the other side.

Unfilled carbon/ graphite seal faces are absolutely necessary in highertemperature applications. Less dense seal faces experience trouble when airtrapped below the surface of the carbon, expands and blows out pieces of carbonfrom the center of the seal face. The exception to this is high temperature oil thatwill coke at the seal faces and pull pieces of carbon away. These resultant pits willcause problems if you are trying to meet fugitive emission standards.

In those pump designs where the open impeller is adjusted back against the backplate (Duriron), any impeller adjustment tends to over compress the seal facescausing high heat. Proper face load is essential to long seal life so cartridgedesigns should be specified any time you use open impellers and high heat is aproblem.

Keep in mind that the pump cooling jacket is also used to cool the shaft that isconducting heat back to the bearings. If you have a high heat application, youmight consider a stainless steel shaft because of its' poor heat conductivitycompared to steel. Some bellows seal manufacturers tend to tell people that theyno longer need the stuffing box cooling and the result is premature bearing failure.

A centerline design pump is always desirable in hot applications to prevent pipestrain at the pump suction and damage to the close clearance wear rings. Insteadof supporting the volute at the bottom this design bolts the pump feet to the sidesof the volute, allowing the volute to expand both up and down. The wet end offyour pump can be modified to this configuration or a new wet end can bepurchased.

If the seal is going to be used in a hot oil application do not hydrostatically testthe seal with water or a water based fluid. Moisture trapped in gaskets, elastomer


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clearances, and other small crevices will flash when it comes into contact with thehot oil, causing a potential damage to the equipment, seal and/ or the people thatmight be in the area.

In cryogenic applications it is not practical to heat the seal area to protect theelastomer. A non elastomer seal with a special self lubricating cryogenic carbon is

your best solution to this application. Be aware that the moisture ladenatmosphere can freeze on the out board side of the seal restricting the sealmovement as the faces wear. In most cases a dual, non elastomer seal with a nonfreezing barrier fluid between the seals is going to be your best choice.


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SUBJECT : Environmental controls and special seals 3-2

For any given seal application problem there are two generally accepted solutions :

Build a special seal that can compensate for the problem once it occurs.

Control the environment surrounding the seal to prevent the problem fromoccurring in the first place. If you control the seal environment you will avoid theinventory and delivery problems associated with special seals.

In the following paragraphs I will be covering each of these environmental controls indetail.

CONTROLLING THE TEMPERATURE IN THE STUFFING BOX AREA.

Flush the stuffing box ( port "C" in the illustrations at the end of this paper) with acompatible, cool, clean liquid. Many seal glands have this connection available in

a more convenient location than the lantern ring connection. Flush is amisunderstood term. It describes six very different functions: Discharge recirculation, where a line is connected from the discharge side of the

pump to the lantern ring connection in the stuffing box (A), or an appropriateconnection in the gland.

Suction recirculation, The recirculation line is connected from the bottom of thestuffing box to the suction side of the pump (A).

Jacketing fluid, The cooling or heating fluid flows through a jacket that issurrounding the stuffing box (B).

Barrier or buffer fluid, The fluid is circulated between two seals either byconvection or by a separate circulation system (E).

Quench, The fluid is passed between the seal and a disaster bushing that has beeninstalled in the rear of the seal gland (D). Flush, A liquid, from an outside source, is injected into the stuffing box at one

atmosphere above stuffing box pressure and dilutes the product a small amount(C).

Use two seals with a cool liquid circulating between them (E). A two waybalanced cartridge seal would be an excellent choice. This arrangement providescooling at the seal faces where it will often do the most good.

Use the jacketed stuffing box that came installed on the pump (figure "B") orinstall one if it is missing. These jackets are available as a replacement part for theback plate on most popular pumps or as an after market bolt on accessory. To usethe jacket properly:

o Dead end the fluid you are trying to control. This means no lines in or out

of the stuffing box except those used to circulate the jacketing fluid.o Install a thermal bushing in the bottom of the stuffing box. Carbon is a

good choice because it is a poor conductor of heat compared to the metalpump components. A typical clearance over the shaft would be 0.002inches per inch of shaft diameter ( 0,01 mm/mm of shaft diameter).


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o Circulate the heating or cooling fluid, through the jacket, to control the

temperature. Six to eight gpm. (25 to 30 liters /min.) is typical of theamount of cool water needed to cool down heat transfer fluid to the pointwhere it will stop "coking" and Viton O-rings will be acceptable. If yourwater is too hard you can substitute condensate or low pressure steam.

An A.P.I. Gland is available for most mechanical seals. The gland has severalfeatures to provide various functions. It can be used as:o A quench connection (Q) to provide heating, cooling, or to remove any

vapors that might escape between the seal faces. Steam can be injected tolower the seal temperature in the event of a fire. In the event of a majorseal failure, this quench connection can be used, in conjunction with thegland disaster bushing, to direct seal fluid leakage to point where it can becollected.

o A flush connection (F) to provide clean fluid to the stuffing box or it can

be used to vent the stuffing box and seal in a vertical pump application.o A close fitting, non sparking, disaster bushing (DB) to provide shaft

support in the event of a bearing failure or to protect personnel in the eventof a massive seal failure. Heat tape or tracing lines can be installed around the stuffing box to provide a

small amount of temperature control. Install a cooler in the line between the pump discharge and the stuffing box. Keep

in mind that this system only works while the pump is operating so it would be ofno value if the problem occurs during pump shut down

Use only balanced seals in these applications to avoid the heat problemsassociated with unbalanced seal designs. Elastomers in the faces and two hardfaces should also be avoided for the same reason.

CONTROLLING THE PRESSURE IN THE STUFFING BOX AREA

Increase stuffing box pressure by installing a recirculation line from the pumpdischarge back to the stuffing box (figure "A") with a close fitting bushing in thebottom of the stuffing box. Try to avoid positioning the recirculation line so that itaimed at the lapped seal faces or thin bellows seal plate materials.

Eliminate the pressure drop between seal faces by using two seals with a higherpressure barrier fluid circulating between them. This is very important in thesealing of chemicals such as ethylene oxide that will penetrate into the elastomer,expand and blow out the other side causing severe damage to the elastomer.

Flush the stuffing box with a high pressure liquid. This is the best solution if the

fluid contains solid particles that could interfere with the seal movement. The only reason to lower stuffing box pressure is because your seal does not have

high pressure sealing capability. It is possible to lower stuffing box pressure bythe use of environmental controls but a high pressure seal would be a much betterchoice. In an emergency you could lower the pressure by one of the followingenvironmental controls:


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o Equalize the pressure in the stuffing boxes, of a double ended pump, by

connecting the stuffing boxes together to get even seal wear. This is acommon application for a double ended centrifugal pump.

o It is possible to lower stuffing box pressure by installing a close fitting

bushing in the bottom of the stuffing box and recirculate to the suction

side of the pump. Be sure to "lock in" the position of this bushing witheither a snap ring or some other retaining device to prevent it from movingtowards the seal. Be careful of using this control on a vertical turbinepump because the high velocity liquid, recirculating to the suction, canheat up the line to the point where it can become "red hot".

o Lower the sealing pressure by utilizing an intermediate fluid pressure

between two tandem or "two way balanced seals"

PROVIDING A LUBRICANT IF THE SEALING PRODUCT IS A NON LUBRICANT( Non lubricants have a film thickness less than one micron)

Use two seals with a higher pressure lubricant as the barrier fluid. This is anexcellent choice in most gas applications or liquids that have little to nolubricating properties. This form of lubrication will often solve the problemsassociated with seal "slipstick" and some other types of vibration.

Flush the stuffing box with a liquid lubricant. Cooling the product will sometimes turn a non lubricant such as hot water into a

lubricating liquid. For some vacuum applications it makes sense to install a discharge recirculation

line to destroy the vacuum in the stuffing box area.

NOTE. If the impeller has been adjusted too close to the back plate the "pump out vanes"

can cause a vacuum to occur in the stuffing box. This often happens if the impelleradjustment has been made backwards (as is the case with Duriron pumps). The problemexists with those open impeller designs that adjust towards the volute (Goulds is anexample).

DECREASING THE AMOUNT OF LIQUID AGITATION IN THE STUFFING BOX.

This becomes very important if you have to seal a liquid that increases its viscosity withagitation. We call these liquids DILATANTS. Connect the bottom of the stuffing box tothe suction side of the pump to allow a single pass of the liquid through the stuffing box.Make sure the connection is very close to the seal faces. You will be better off using the

seal gland flush connection rather than the stuffing box lantern ring connection.

Some liquids decrease their viscosity with agitation. We call these liquidsTHIXOTROPHIC. In some instances the thinner liquid film can cause more face wearand seal "slip stick". If this problem exists use one of the environmental controlsmentioned above.

HANDLING SLURRY APPLICATIONS.


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Flush with a clean liquid. Check with your seal manufacture for the minimumamount of flush that is needed. Balanced seal designs with the springs locatedoutside of the fluid and most metal bellows designs require only one to twogallons (4 to 8 liters) per hour.

o Note: this is per hour not per minute. At shaft speeds below 2900 rpm.

filling the seal cavity with a compatible grease is usually satisfactory. Increase the seal clearance in the stuffing box area. Replacement back covers with

extra large stuffing box designs are available for most pumps. Bolt on, largediameter stuffing boxes are also available in the after market. If your product iscool you can probably run the fluid "dead ended" with no connections cominginto or out of the stuffing box.

If you product contains sub micron particles as is the case with Kaoline (chinaclay), you will have to circulate a higher pressure clean liquid between two sealsto prevent solids penetration between the faces. In some cases two hard faces alsohelps. Almost any dual seal design is acceptable with the exception of the "backto back" rotating design which is never acceptable in any application.

Recirculate to the suction side of the pump when possible. This will circulatecleaner fluid from behind the impeller, through the stuffing box, and then back tothe suction side of the pump. Original equipment manufacturers do just theopposite by having the stuffing box fitting connected to the discharge side of thepump.

o CAUTION! Do not connect to the suction side of the pump if the fluid is

being pumped at or near its vapor point as this could cause flashing in thestuffing box location. If the solids have a low specific gravity (they floaton the liquid) you may have to go to a clean liquid flush becausecentrifugal force will work against you.

Any time that you deal with a slurry application you are going to have a couple of

other problems as well so be prepared for them:o Frequent impeller adjustment and excessive wear ring wear. You will need

a cartridge seal or a sleeve mounted split seal to compensate for theimpeller adjustment. Cartridge seals can generally be reused if the pumphas been disassembled to replace the wear rings.

o Vibration will increase as the impeller goes out of balance due to abrasive

wear. This can cause drive lug wear and carbon face chipping. Vibrationdamping will become very important. Seal designs that incorporate O-rings have a built in natural vibration damper. Metal bellows seals requireanother solution.

o Wear of the rotating components. This is especially true if the seal rotates

in the fluid. Better seals are designed to cause rotation of the fluid in theseal chamber.

If you prefer to solve the application problem by using a special seal. the followingthoughts might help in deciding your selection.

SEAL DESIGN FEATURES THAT ADDRESS THE PROBLEMS OF EXTREMES INHOT AND COLD.


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Metal bellows seals. An excellent choice for cryogenic and high temperature, nonpetroleum liquids. Petroleum products "coke" in the presence of high heat socooling is necessary in these applications.

Carbon / metal composites to conduct heat away from the seal faces. Do not use"glued in" versions.

Elastomers located some distance from the seal face to protect the elastomer(rubber part) from the additional heat generated at the seal faces Low friction face combinations. Carbon / tungsten carbide or Carbon/ silicone

Carbide are among the best. Some duplex material faces are showing good resultsin these applications. Carbon impregnated silicone carbide is an example of sucha material.

Elastomers that have a wide range of operating temperature. Kalrez is a goodexample.

Low expansion metals such as Carpenter 42 and Invar 36 that will still retain thecarbon or hard face in the holder even though the temperature changes greatly. Beaware that low expansion metals have poor chemical resistance so be careful in

using them. Stationary seal designs are subject to a differential temperature across the seal

face and body if a recirculation line or flush is being used. This differentialtemperature can cause the face to go out of flat. You will be better off with arotating design in this instance.

If you elect to solve only the sealing problem you must keep in mind that the extremes inheat and cold will also affect the bearing seals as well as the bearing oil. Unless youaddress these problems separately you will be better off controlling the temperature in thestuffing box area and solving most of the bearing area problems at the same time.

SEAL DESIGN FEATURES THAT ADDRESS THE PROBLEM WITH SLURRIES.

Springs out of the fluid, the most common place to clog a seal. Vibration damping because the wear causes the rotating assembly to go out of

balance. Be sure the dynamic elastomer moves to a clean surface as the seal carbon face

wears. Use centrifugal force to clean the sliding seal components. Rotating seals (the

spring loaded face rotates) should be your first choice. Non stick coatings on the metal parts to prevent a build up of solids on the sliding

components. These coatings are porous so do not use them for corrosionresistance.

If possible, rotate the slurry to reduce seal component wear. In future papers I willaddress the problem of sealing individual applications. In the mean time the aboveinformation should help you to get started.


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Dupont Dow elastomer


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SUBJECT: Some more about condensate 10-7

What is condensate?

Steam that has been condensed back into water by either raising its pressure or

lowering its temperature. Not to be confused with demineralized, de-ionized,make up, or softened water. When the condensate enters the boiler feed pumpadditional chemicals are added and the product is now called boiler feed water.

Where does condensate come from?

Condenser hotwells, the bottom part of the condenser Steam traps. They trap steam in the lines and let the condensate drain through. Heat exchangers. Condensate must be removed to allow the heat transfer. The

condensate flows to the bottom where the steam trap will open and allow thecondensate to flow to the receiver. There must be a positive differential pressure

between the heat exchanger and the condensate line so that the condensate willflow out of the heat exchanger. If the differential pressure is not there a pump willhave to be installed to remove the condensate.

Or any other place that you are using steam.

We want to keep dissolved oxygen out of condensate. Why?

It changes the pH of the water. This will contribute to corrosion problems in thesystem. Especially the boiler.

o Boilers like a ph of somewhere between 10 and 11.

o Hot water is almost the perfect solvent. Give it enough time and it will

dissolve anything. Remember that boilers have to last thirty years or more.This means that water has plenty of time to do its damage. It is the oxygenin the condensate that makes condensate a strong oxidizing agent that canattack metals.

Some carbon seal faces can be attacked by high oxygen levels in the condensate. The more gases entrained in the condensate the more likely the pump will

experience cavitation problems. The condensate temperature determines the amount of dissolved oxygen. You are

trying to conserve the energy (temperature) that was added to the steam to keepthe amount of dissolved oxygen down

TEMPERATURE F. TEMPERATURE C. PPM DISSOLVED OXYGEN30 1 10 ppm

90 32 5 ppm

120 50 4 ppm

150 65 3 ppm

180 82 2 ppm


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210 100 0 ppm

The average level detected in condensate receivers is three parts per million. This isalmost one thousand times greater than the five parts per billion level that can inducepitting corrosion.

How does oxygen get into the condensate system?

Through the packing of condensate pumps. The stuffing box is under a negativepressure, and air that is one third oxygen, leaks in.

Valves above the water line can introduce oxygen as the velocity of the waterlowers the pressure at the valve stem.

Flanges can have the same problem as valves. Oxygen is dissolved in makeup water that was added to the boiler because of

condensate leaks. Pumps with built in repellers that create a negative pressure in the pump stuffing

box.

How do you get rid of the dissolved oxygen?

Add chemicals to convert it. Hydrazine is an example. You are adding hydrogenthat will combine with the oxygen to form water.

In nuclear applications it is common to add hydrogen to the system for the samereason. Hydrogen and oxygen will combine to form water in a neutron flux.

Deaerate the condensate. This is normally done by heating the condensate withsteam in a deaerating tank that is located close to the suction of the boiler feedpump.

Use balanced, O-ring mechanical seals that will prevent air from coming into thestuffing boxes of condensate pumps.

Seal valves and flanges to prevent air from entering the system.

Why do we have to use so much "make up" water in our boiler ?

Because we lose so much of it.o Condensate pump discharge recirculation lines that are trying to put a

positive pressure on packing are a common source of condensate loss.o Boiler blow down is a major problem. Some boilers run with a constant

blow down because air that is entering the system is changing the pH of

the water, causing chemical addition that increases the total solids, causingthe need for additional blow down..

o Steam tools.

o Air ejectors that are used to create a vacuum in receivers etc.

o Steam traps that drain to the ground.

What are some methods for conserving condensate?


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The discharge recirculation line used with packed pumps is a big waste. Convertto a balanced o-ring seal and save a pile of condensate.

Stop air from entering the system. The air is causing frequent boiler blowdowns.You can easily seal flanges, valves and rotating shafts.

Do not drain steam traps to the ground. Collect it in a tank that can be pumped

back into the system. If condensate is being circulated through the cooling jacket on a pump, make sure

it is not being discharged to a drain. There is no reason it cannot be returned to thecondensate system.

If condensate is being circulated between dual mechanical seals, it is not a goodidea to return it to the condensate system. There is too a high probability ofcontaminating the condensate with product leakage.


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SUBJECT: The sealing of high pressure and hard vacuum 5-7

High pressure does three things that will damage any mechanical seal :

It will create a high axial hydraulic load on the seal faces. This load will be in

addition to the axial force created by the single spring, multiple springs, or metalbellows that are used to create the initial face loading in popular seal designs. Thisexcessive axial loading can:

o Generate heat that could be detrimental to one or more of the seal

components such as the elastomer or in some cases, the product that youare sealing.

o It can cause excessive wear in a short period of time. This will be a very

important consideration when you are sealing non, or poor lubricatingfluids. Thixotrophic fluids (they lose their viscosity when agitated) willalso be affected.

o If the product is a poor lubricant or a non lubricant, a high axial load can

cause "slip stick" problems that can chip the carbon outside diameter andpossibly open the lapped seal faces.o It can change critical dimensions, such as the lapped seal faces going out

of flat. It can distort one or more of the seal components causing the lapped seal faces to

go "out of flat."o Seal faces are subjected to "hoop stresses" that attempt to shrink the

material. Since these faces are seldom designed as a "solid block" theaffect is to alter the lapped face flatness. Finite element analysis designtechniques help, but are still limited in practice.

High pressure can extrude the elastomer (rubber part) in many seal designs, either

"locking up" the seal or causing leakage where the elastomer was extruded. Inalmost every case the elastomer suffers permanent damage.

The excessive hydraulic pressure can come from several sources that include:

The normal system pressure. In most single stage pump applications the stuffingbox pressure is slightly higher than suction pressure, but multi stage pumpapplications, boiler circulating pumps, and some pipe line service pumps canexperience very high stuffing box pressures.

Water hammer and pressure surges can cause a very high temporary pressure inthe system.

Unusual system operation is another cause. The rapid opening and closing ofvalves can cause these surges of pressure. A loss of power to a running pump can cause vacuum pockets in the lines. As the

liquid rushes to fill up these vacuum voids, very high pressures can beexperienced.


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The solution to high pressure sealing falls into three separate categories. You must decidewhich of the approaches makes the best sense in any given application. The threeapproaches you can use are:

Build a seal that can handle the excessive pressure.o

Select hydraulic pressure balanced seal designs to lower the axial load.o Higher modulus materials are seldom available. You will have to go to a

finite element stress analyzed design. Look for seal components that haveuniform thickness cross sections, or go to larger cross section seals thatwill require more stuffing box radial room.

o Laminated bellows are available for many higher pressure metal bellows

applications (same principal as plywood).o Higher durometer O-rings with non-metallic back up rings are available to

prevent elastomer extrusion. Stage the seals in an application so that several seals will be sharing the pressure.

o Tandem sealing with an intermediate lower barrier fluid pressure is the

most common. In some nuclear applications three seals have beenconnected in tandem to handle the high pressure. Tandem and other typesof multiple seal arrangements take a great deal of axial room. In everycase you are moving the first seal further away from the bearings so shaftstabilization becomes very important. You should also remember that themultiple units are acting as a single seal. In other words if you fail one ofthe seals, you fail them all.

Lower the pressure in the stuffing box.o Locking a restriction bushing into the bottom of the stuffing box and then

connecting a suction recirculation line from the bottom of the stuffing boxto a lower pressure location in the system is the normal way to accomplish

this. Watch out for erosion of this bushing, especially in abrasiveapplications. Be aware that if stuffing box pressure is near the productvapor pressure, flashing could occur in the stuffing box or between thelapped seal faces.

o You can cross-connect stuffing boxes in a multiple stage, double ended

pump design. Keep in mind that this will not work with single stagecentrifugal pumps.

Vacuum means less than atmospheric pressure and vacuum sealing falls into twocategories:

Normal vacuum. This vacuum is usually measured in inches or millimeters of mercury.

This is the vacuum found in condensers, evaporators and at the suction side of thepump every time you use the centrifugal pump to lift liquid.

Hydraulic balanced seal designs can handle this vacuum because vacuum onlymeans one atmosphere of pressure (15 psi. or one bar) coming from the other sideof the seal.


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O-rings are preferred for the elastomer design. Continuous O-rings can seal eithervacuum or pressure. They also have the ability to flex and roll to compensate forshaft movement.

Carbon metal composite seal faces are satisfactory as long as the carbon is sealedat the inside diameter to prevent the pressure from penetrating behind the carbon,

upsetting the hydraulic face balance and possible blowing the carbon out of itsholder.

Hard vacuum. This vacuum is normally measured in microns, micro inches, or portionsof a millimeter of mercury (Torr).

Elastomers are not acceptable for hard vacuums. The vacuum will cause theelastomer to "out gas" increasing the elastomers' density and reducing the volumeto a point where leakage is possible. All metal seal designs will probably be yourfirst choice.

Seal face density and self lubrication can be a real problem in hard vacuum

applications because of the lack of moisture to release the graphite from thecarbon/ graphite compound. Conventional seal designs are seldom satisfactory inthese applications. A great many materials exist that can solve the problem, soyou will want to contact your seal supplier for the availability of higher densityand self lubricating carbons for these special applications.

Tandem dual seals with a higher pressure lubricating barrier fluid is the mostcommon solution to hard vacuum sealing.


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SUBJECT : The sealing of hot oil 3-5

The largest user of hot oil pumps is the heat transfer oil customer. Many consumers usethese products with oil temperatures exceeding 500 Fahrenheit (260 C.) and 600 to700 F. ( 315 to 370 C.) becoming common. Some hotels have recently installed these

systems in their laundry to dry clothing.

Heat transfer oils have many advantages over the steam that was formally used in theseapplications.

The product does not flash. No boiler blow down. No deaeration heat loss. No high pressure. This means it is not only safer but also tends to leak less. No licensed boiler operator needed. The temperature can be kept uniform over a large processing area.

You can heat and cool with the same system. These oils are excellent in systems that are water/ steam sensitive. The product is kept in a closed system. This means that all leakage can be

stopped. There is less corrosion in the system.

In addition to these heat transfer oils you will encounter hot petroleum oil applications inrefineries and hot organic oil applications in various other industries. There are severalproblems associated with sealing these hot oil products and each of them has to be solvedif satisfactory seal life is ever to be obtained.

High temperature oil is generally too hot for most commercially availableelastomers. (the rubber parts) The product "cokes". These coke particles form at the elevated temperatures and

coat them selves inside the system piping, hardware and on the mechanical sealworking parts. These "coke" particles restrict the movement of sliding/flexing sealcomponents causing the lapped seal faces to open. The amount of coke that formsis a function of time and temperature. In other words, coking will be a moresevere problem in a closed loop system than it will be in the oil refining business.Contrary to popular opinion testing has shown that air or oxygen is not needed forthe formation of coke. This means that seal designs that try to eliminate theoxygen by quenching or some other method will not work. The use of steamquenching is limited to its' cooling effect only.

The product is always a fire hazard and depending upon the type and brand youpurchase, there could be toxicological problems. Keep in mind that the seal isgoing to wear out or fail at some time and the product will leak out to theatmosphere.

Thermal growth of the pump parts will cause problems in maintaining properpump "wear ring" and impeller clearances, as well as the correct sealcompression.


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Misalignment between the driver and the pump and between the piping and thepump suction is a serious problem at elevated temperatures.

The product is costly. Leakage represents large monetary losses and personneldanger as well as environmental problems.

Heat tracing must be provided throughout the system to prevent the product from

becoming too viscous during periods of prolong shut down. No one ever heattraces the stuffing box. Vibration is always a problem with hot oil pumps because the coke attaches to

rotating components interfering with the dynamic balance. You always end up pumping a slurry which means frequent impeller adjustments

or wear ring replacement and excessive vibration due to the imbalance caused bywear of the rotating parts.

As the coke builds up on the inside of the discharge piping the pump will operatefurther off of its best efficiency point (B.E.P.) causing shaft deflection, vibration,and excessive seal movement. Coking on the inside of the suction piping cancause cavitation problems

Although there are many techniques available to the seal man to address each of theseproblems the combination of these problems eliminates most of the common techniquesand leaves the customer with very few options to get good seal life. Regardless of the sealselected you must address all of the problems or the seal life will be shortened.

Oil refineries pump hot oil with closed impeller pumps and as a result have to put up withthe additional problems associated with replacing "closed impeller" wear rings. Unlikethe chemical industry they cannot take advantage of the features of an open impellerdesign that can be easily adjusted to maintain maximum efficiency. There are two reasonswhy oil refineries chose closed impeller designs with mechanical seals and A.P.I. glands :

Fear of a bearing failure that could cause sparking as the metal impeller contactedthe metal volute. The soft non sparking, metal wear ring on one end of the shaftand the carbon disaster bushing installed in the A.P.I. Gland on the other, wouldinsure no hard metal contact if a bearing failed as the shaft was turning.

Shaft expansion or impeller adjustment could cause the rotating, open impeller tocontact the stationary volute. To prevent sparking the impeller or volute wouldhave to be manufactured from a soft non sparking metal such as aluminum orbronze and this would not be very practical.

To insure long seal life you must do the following:

The product has to be cooled in the seal chamber :

The oil must be cooled to stop the coking. Coke is a function of heat. Many yearsago it was believed that oxygen had to be present for coking to occur, but testinghas shown that this is not true. You can coke any petroleum product in an inertatmosphere as long as the temperature is high enough. The finest lubricating oil


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available will start to coke at 300 F (150 C). The amount of coking that you getis determined by the oil temperature and time.

The oil must be cooled to prevent damage to any elastomers that might beinstalled in the seal or shaft sleeve. Elastomers that are subjected to high heat willfirst take a compression set and then shrink in volume. They will eventually grow

hard, crack and leak excessively. The oil must be cooled to reduce the amount of heat that will be transferred

through the shaft to the bearing oil or grease. This heat will reduce the viscosity ofthe lubricating oil or grease and eventually cause premature bearing failure. TheSKF bearing company states in their lubrication literature, that the life of bearingoil is cut in half for each ten degrees Centigrade (18 F) increase in bearing oiltemperature. They recommend 60 C to 70 C (140 F to 158 F) as an ideal oiltemperature.

The grease or lip seals are sensitive to any increase in shaft temperature. Astainless steel shaft is a good choice in these applications because stainless steel isa poor conductor of heat compared to carbon steel. This is the reason there are no

stainless steel frying pans unless they are clad with either aluminum or copper.

You must install a back up seal for the following reasons:

The product is dangerous. Leaking hot oil can start a fire or injure any personnelin the area. Many brands are toxic and some have been identified as possiblycarcinogenic.

The product is too costly to tolerate even small amounts of leakage. Back up cooling is necessary if the primary cooling method fails. A back up seal,

with a cool barrier fluid system, can provide this cooling If you elect not to use a back up seal, then be sure to install an American

Petroleum Institute (A.P.I.) type gland. Look at the following illustration. Thegland can perform several functions for you:

The disaster bushing can provide shaft support if you lose a bearing.

The leakage will be directed to the quench and drain connection when the sealwears out or fails.

The quench connection will allow you to use steam for product cooling, but donot use too much because it could penetrate into the bearing case.

You can connect steam to the quench connection and use it to put out a fire,should it occur on the outboard side of the seal.

In this application the flush connection is not used. The stuffing box is "deadended" to take full advantage of the heating/ cooling jacket.


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A large diameter cooled sealing chamber should be installed on the pump.

To allow centrifugal force to throw solid coke particles away from the seal facesand sliding or flexing components

Misalignment is always a problem in these pumps. This shaft displacement can

cause the rotating seal to rub against stationary parts in a conventional stuffingbox. Vibration means movement . The seal must be free to move within the seal

chamber. When the pump stops gravity will pull solid particles to the bottom of the stuffing

box. A large seal chamber will almost guarantee that the particles will not collectaround the seal at this time.

A Cartridge seal is necessary.

Thermal growth will cause volute casing and shaft expansion. Only a cartridge

seal will compensate for this movement and allow for the impeller adjustment thatwill be necessary. The wear caused by the slurry will cause frequent impeller adjustments. The

average pump used in these applications has almost 0.250 inches (6 mm) ofadjustment possible.

To compensate for misalignment you will have to :

Use a "C" or "D" fame adapter to compensate for misalignment between the pumpand its driver.

o These adapters are available from all good pump companies and will

compensate for misalignment as the pump goes through its temperaturetransients.o No other method of alignment works any where near as well. If you are

going to do a conventional alignment with dual indicators or a laseraligned be sure your calculations compensate for thermal growth.

Use a "centerline" wet end to prevent excessive wear ring wear and pipe strain atthe pump suction. If your pump did not come equipped with this type of wet endit can easily be installed in the maintenance shop. Look at the followingillustration:

The illustration shows the centerline design. It will allow the pump volute to thermally

expand both up and down, and thereby eliminate strain on the suction piping.


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Now that we have discussed these important points lets take a look at some solutions thatare often offered, but that we should not adopt as our solution. Here are the things that donot work well :

Bad solution #1. Use a metal bellows seal to eliminate the need for cooling in the sealarea.

Comment: Although the metal bellows does not have rubber parts that are sensitive tohigh temperature cooling is still needed for the coking. Most bellow suppliers offer anA.P.I. type gland to provide low pressure steam behind the seal for cooling purposes andthereby eliminate the option of backup sealing. This quenching should be limited to onlya back up cooling status. If quenching is done with water rather than steam, watch out fora calcium build up outboard of the seal. This "hard water" build up can restrict themovement of the flexing portion of the seal as it tries to compensate for face wear.

If you substitute condensate for the quenching fluid the build up can be eliminated almostentirely.

Bad solution #2. Run a line from the discharge of the pump through a cooler and filter tocool down and clean up the oil going into the stuffing box.

Comment: The problems with this solution are obvious. The filter will clog andthe cooler will become inoperative as coke builds up on the tubes.

Bad solution #3. Use two seals and run a cool oil between them.

Comment: You have addressed the cooling problem but you have not addressedthe problem of the slurry with this solution.

What then is the best solution that addresses all of the problems? Look at the followingillustration:


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Install a large jacketed sealing chamber. These bolt on accessories are availablefrom your local pump/seal supplier. Many suppliers can provide a replaceablepump back plate with a large seal chamber cast into the plate

Dead end the stuffing box. In other words no lines coming into or away from the

inner seal chamber. Do not worry about the heat. With a six to eight gallon perminute( 20 to 30 liters/ minute) flow through the cooling chamber the coolingjacket can keep the temperature down to 200 to 250 Fahrenheit (95 to 120 C.)without any trouble. If you have hard water in your area, condensate may be thebest choice to use as the cooling medium. In some cases low pressure stream issatisfactory. If you anticipate long periods of shut down, low pressure steam willbe your best choice as it will keep the heat transfer oil at the proper low viscosityduring these shut down periods.

Install a cartridge dual seal that has the inner seal balanced in both directions. Ifthe pump does not have precision bearings a double motion seal with the samefeatures will work just as well. "Two way" balance is necessary because the

system and barrier fluid pressure can and will vary. The dual seal is necessary to conserve the expensive product and to provide a

safety feature when the inboard seal wears out or fails. It will also allow you timeto schedule a seal replacement.

Install a convection tank between the two seals and use cool heat transfer oil asthe barrier or buffer fluid. A lower pressure or buffer fluid is preferred. A slightpressure on the tank will allow you determine which seal has worn out or failedfirst. A pumping ring or forced lubrication between the seals is necessary

Install a carbon restrictive bushing into the bottom of the stuffing box to act as athermal barrier. Applications have worked without this bushing but not as well aswith it. Any material that has poor heat conductivity will work as well as carbon

as long as it is non sparking and dimensionally stable.

That is all there is to the application. Centrifugal force will clean up the small amount offluid in the sealing chamber while the cooling jacket holds the temperature low enough toprevent coking and injuring the seal elastomer.

The only problem with this system is that it works so well we often forget to clean thecooling jacket on the pump. A small layer of calcium inside this jacket will provide an


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SUBJECT : The sealing of hot water 3-3

Water is normally considered a good lubricant and can do an adequate job of providinglubrication between the lapped faces of a mechanical seal, but there are a few problems:

At elevated temperature the water lub

sealing common fluids

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