seal off centrifugal pump problems and seal basic selection.docx

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Seal Off Centrifugal Pump Problems

Paying proper attention to seals can improve pump

performance and life.

Seals play a crucial role in centrifugal pumps. They serve at both the "dry" and "wet" ends of the

pumps, primarily to retain lubricant, exclude contaminants, separate fluids and confine pressure.Without effective seals, contaminants (solid or liquid) can find openings to infiltrate both the

lubricant and bearings -- leading to potentially dire consequences impacting both the cleanliness

and integrity of the lubricant and the life of the bearing. And, in cases where seal failure causes

lubricant loss, dry-running operation can prompt premature and rapid deterioration of bearings

and, in turn, the pump.

The correct specification of seals consistent with operating conditions ultimately can helpmaximize component service life and keep pumps up-and-running as intended.

THE BASICS Bearings in centrifugal pumps support hydraulic loads imposed on the impeller, the mass of the

impeller and shaft, and loads due to couplings and drive systems. They also keep shaft axial and

radial deflections within acceptable limits for the impeller and shaft seal.

Dynamic radial shaft seals, which come in a variety of designs and materials, commonly protect

the power frames of API heavy-duty process pumps and ANSI light- and medium-duty class pumps; bearing isolators or labyrinth-type seals usually are located at the pump's wet end. Many

API pumps are migrating gradually to bearing isolators at both the thrust and line ends.



Bearing Isolator

Figure 1. Maze-like internal structure collects and ejects contaminants before they can intrude.

In general, dynamic radial seals create a barrier between surfaces in relative motion (one usuallyis stationary while the other rotates). These seals -- more often than not made from nitrile rubber

-- may feature a plain, wave or helix lip design. In many cases, a garter spring holds the primary

sealing lip in position and also promotes oil retention. Standard seals usually incorporate asimple L-shaped shell with the sealing material bonded to it; others also may include an inner

shell to help protect the lip from damage or distortion during installation.

Bearing isolators or labyrinth-type seals (Figure 1) provide highly effective exclusion

capabilities. Instead of a contacting radial lip element, these seals rely on a labyrinth or maze-

like internal structure to collect and eject contaminants before they can intrude. Designs typicallyintegrate a stator pressed into the housing and a rotor fixed to and turning with the shaft. The twocomponents are locked together for easier assembly and to prevent damage during handling.

Standard versions usually will incorporate polytetrafluoroethylene (PTFE) for the structural body

material and fluoroelastomer O-rings to promote high chemical and temperature resistance.

MAKING A CHOICE Seal specification for centrifugal pumps begins with identifying the correct general design for the



application, followed by proper sizing of the hardware (never mix inch and metric dimensions

and tolerances). Then, for optimized seal performance, evaluate all relevant operating conditions

to narrow the field.

Important operating parameters to consider include:

Surface speed . Radial shaft seals are designed to perform within designated surface speed limits.

Generally, surface speed capability is inversely related to parameters such as seal torque, power

consumption, under-lip temperature and the effect of dynamic run-out. All these speed-relatedinfluences can affect seal life.

Damaged Seal

Figure 2. Arrows show where seal has suffered intrusions from foreign matter.

The majority of standard small-bore (under 8 in. shaft diameter) radial seals are rated up to 3,600ft/min, while larger diameter seals are rated to approximately 5,000 ft/min. PTFE bearing

isolators usually can work at up to 5,000 ft/min, while metallic versions can handle 10,000

ft/min. An application calling for higher speeds requires specialized design considerations.

Options to help mitigate the negative effects of higher shaft speeds include reducing the radialload on the seal lip, switching to a sealing material that can handle higher temperatures, changing

lubricant type or viscosity, optimizing the shaft sealing surface or using a non-contacting

labyrinth seal design.

Pressure. Standard radial seals are designed for only about 7 psi. System conditions or a fault

such as a plugged vent can mechanically load and distort a seal's lip profile, resulting in rapid

wear and failure. Solutions to compensate for the effects of pressure include pressurizing the sealcavity to allow the seal to serve as a main pressure retention seal, and redesigning lip profiles to

resist deformation under pressure loading and moderate surface speeds.

In situations where higher shaft speeds will be encountered, the permissible pressure differential

across the seal becomes smaller. As pressure is applied to the seal, more lip surface is forced

against the shaft, which produces greater friction (as does increased shaft speed). Too muchfriction leads to faster wear and shorter life of seal and shaft -- so, pressure and surface speed

must be balanced against each other for maximized seal performance.



Temperature. Operating a seal material beyond its recommended temperature range can cause

thermal stress that will harden the compound; the hardening often appears as a series of radial

cracks on the seal. (Historically, such heat aging of nitrile rubber seals has represented a morecommon cause of failure than wear.) Changing the seal material from rubber to PTFE or

fluoropolymer can raise a seal's thermal limit.

Surface finish. Shaft surface roughness and directionality rank second only to heat damage as

culprits for leakage. Under a microscope, a shaft's surface can be mapped as a series of peaks and

valleys. Too smooth a surface may not support an oil film, which can result in a higher-than-desired under-lip temperature. If a surface is too rough, peaks can project through the lubricating

film and abrade the lip. The best practice is to consult the roughness and texture specifications

developed by manufacturers and based on industry standards. Additionally, consider using

electronic tracing instruments to assess surface finishes accurately.

A shaft also may exhibit directional lead (a spiral or screw pattern) from the initial turning or

grinding method. While an inward lead might prove beneficial in some respects, an outward

pattern can result in more oil under the lip than its pumping action can handle. Keep the potentialconsequences in mind and inspect shafts accordingly.

Media. Nitrile rubber performs well with a wide range of mineral-based oils as lubricants.

However, polar solvents such as acetone can lead to catastrophic swell (observed as a softening)

and physical destruction of the seal. Similarly, compounds such as ethylene propylene will swellrapidly from contact with aromatic hydrocarbons and mineral oils. And some lubricants based on

synthetics, while resisting oxidation, can attack rubber compounds. The appropriate marriage of

seal and lubricant can help avoid seal degradation and contribute to improved performance.

Lip Wear

Figure 3. Inner diameter of seal exhibits uneven lip wear, as indicated by arrow.

TROUBLESHOOTING SEAL FAILURES Despite all the advances in sealing system designs, materials and performance over the years,

seals aren't immune to potential failure -- many times for reasons other than the seals themselves.

Picking an inappropriate replacement, improper installation or switching or mixing lubricant cancause problems over time. When good seals go bad, the best troubleshooting practice is to ask

the right questions and then follow a logical sequence of steps to analyze the failures and take

remedial action.



Questions that will help to pinpoint failure causes include:

How well has the seal performed in the past and is it the correct seal for the application? If there's a history of failures with a particular seal, the culprit may not be the seal itself -- unless

the seal isn't the right design or the material is inappropriate for the application. At the first signs

of failure, such as intrusion of foreign matter (Figure 2), check the seal's part number and reviewrecommended applications to exclude the seal itself as suspect. Then, via a process of

elimination, focus on the many influences that can impact seal performance and service life.

Always check whether operating conditions conform to the optimum range specified for the seal.

Subjecting a seal to operating conditions outside that range surely will result in its failure. For

example, when operating temperature or pressure exceeds the lip material's maximum, the sealmay exhibit heat cracking, which is indicated by a hardened seal lip or fine cracks visible in the

seal lip surface. Excessive surface speeds or insufficient lubrication at the seal lip can eventually

lead to heat cracking and damage.

Shaft-to-bore misalignment or dynamic run-out can cause early lip leakage, excessive anduneven lip wear on one side of the seal (Figure 3) or excessive but consistent lip wear all

around. (Shaft-to-bore misalignment results from inaccurate machining, shaft bending, lack of shaft balance or worn bearings; dynamic run-out is a similar condition where the shaft doesn't

rotate around its true center.) The seal's lip area with the greatest wear will indicate the direction

of the misalignment.

FOLLOW A FEW GUIDELINES

These pointers, which apply to all types of seals, will help ensure effective protection of your pump:

Never re-use worn seals.

Properly store seals in a cool area (not work area) at 40 –

70% humidity. Ensure packaging is intact and inspect the seal's lip for possible distortion from improper

handling.

Use the correct installation tools.

Keep the area clean and free of contamination.

Select the correct seal for the speed.

Pick the proper seal for the pumped medium.

Check the operating temperature against lip material specifications.

Verify the lubricant (including additives) is compatible with the seal lip material.

Confirm the leading edge of the shaft is chamfered.

Make sure shafts are hardened to Rockwell C 30 or harder.

Validate tolerances for the shaft diameter are within range.

Wherever possible vent equipment to help prevent pressure buildup.

A breakdown in lubrication or improper lubricant also can lead to problems. Sometimes heatmay be high enough to break down the lubricant but not enough to harden the seal's lip. In such

cases, sludge or varnish-like deposits will accumulate on the seal lip and damage will occur.

Using the proper lubricant and regularly changing it are among the best practices to help avoid

lube-related seal failures.



Improperly installed seals likely will fail quickly. Symptoms of damage caused by a hammer

blow during installation include visible dents on the seal back, a distorted sealing element or a

garter spring that pops out. All are causes for concern and necessitate seal replacement.

Other factors ranging from possible media intrusion to undue pressure within a seal cavity can

compromise seal performance. Also, it pays to review maintenance and operating practices to seeif they could adversely impact sealing systems.

The central message here is to confirm the seal has been installed properly, runs within specifiedoperating condition ranges and benefits from the proper lubricant.

What is the source of the leak? It's helpful as a reference point to determine whether the leak is in

the inner or outer diameter of the seal. If you can't locate the leak, add ultraviolet dye to the sump

or spray white powder on the area. After operating for 15 minutes, use ultraviolet light to show

the leakage source. In addition, documenting when the leak first occurred may relate it to achange in maintenance or operating procedures.

What are the initial best practices when analyzing failures? When a seal fails, follow these five basic steps:

1. Inspect the seal before removal. Check the condition of the area, note the amount of leakagethat has occurred and determine the source of the leakage.

2. Wipe the area clean and inspect for:

• nicks on the bore chamfer;

• seal cocked in the bore;

• proper seal installation;

• shaft-to-bore misalignment;• seal looseness in the bore;

• seal case deformation; and

• paint on the seal.

3. Rotate the shaft to ascertain whether there's excessive end-play or run-out, which can indicatemisalignment issues.

4. After removing the seal, check for:• rough bore surface;

• shaft cleanliness (clean and free of carbon?);

• coked lube on the shaft; • shaft damage; • f laws or voids in the bore;

• shaft corrosion; and

• shaft discoloration.

5. Identify the seal style and materials and inspect for:

• primary lip wear;



• primary lip conditions;

• wear or damage to the seal's outer diameter; and

• spring damage.

Your observations will help pinpoint the failure's root cause and appropriate remedial actions to

prevent repetition.

SUCCEED WITH SEALS Optimizing a sealing system truly is a balancing act. Carefully identifying the application'srequirements, evaluating all conditions and adopting a holistic approach to seal specification

with a system-wide perspective will contribute significantly to how a seal performs and for how

long. Partnering with an experienced manufacturer of bearings, seals and lubricants can helpmaximize system potential and minimize problems.

Sealing The proper selection of a seal is critical to the success of every pump application. For maximum pumpreliability, choices must be made between the type of seal and the seal environment. In addition, a

sealless pump is an alternative, which would eliminate the need for a dynamic type seal entirely.

Sealing Basics There are two basic kinds of seals: static and dynamic. Static seals are employed where no movementoccurs at the Juncture to be sealed. Gaskets and O-rings are typical static seals.

Dynamic seals are used where surfaces move relative to one another. Dynamic seals are used, for example, where a rotating shaft transmits power through the wall of a tank (Fig. 1), through the casing of a pump (Fig. 2), or through the housing of other rotating equipment such as a filter or screen.

Fig. 1 Cross Section of Tank and Mixer



Fig. 2 Typical Centrifugal Pump

A common application of sealing devices is to seal the rotating shaft of a centrifugal pump. To bestunderstand how such a seal functions a quick review of pump fundamentals is in order.

In a centrifugal pump, the liquid enters the suction of the pump at the center (eye) of the rotating impeller

(Figures 3 and 4).

Fig. 3 Centrifugal Pump, Liguid End

Fig. 4 Fluid Flow in Centrifugal Pump



As the impeller vanes rotate, they transmit motion to the incoming product, which then leaves theimpeller, collects in the pump casing, and leaves the pump under pressure through the pump discharge.

Discharge pressure will force some product down behind the impeller to the drive shaft, where it attemptsto escape along the rotating drive shaft. Pump manufacturers use various design techniques to reducethe pressure of the product trying to escape. Such techniques include: 1) the addition of balance holes

through the impeller to permit most of the pressure to escape into the suction side of the impeller, or 2)the addition of back pump-out vanes on the back side of the impeller.

However, as there is no way to eliminate this pressure completely, sealing devices are necessary to limitthe escape of the product to the atmosphere. Such sealing devices are typically either compressionpacking or end-face mechanical seals.

Stuf f ing Box Packing A typical packed stuffing box arrangement is shown in Fig. 5. It consists of: A) Five rings of packing, B) Alantern ring used for the injection of a lubricating and/or flushing liquid, and C) A gland to hold the packingand maintain the desired compression for a proper seal.

Fig. 5 Typical Stuffing Arrangement (description of parts)

The function of packing is to control leakage and not to eliminate it completely. The packing must belubricated, and a flow from 40 to 60 drops per minute out of the stuffing box must be maintained for proper lubrication.

The method of lubricating the packing depends on the nature of the liquid being pumped as well as on thepressure in the stuffing box. When the pump stuffing box pressure is above atmospheric pressure and theliquid is clean and nonabrasive, the pumped liquid itself will lubricate the packing (Fig. 6).



Fig. 6 Typical Stuffing Arrangement when Stuffing Box Pressure is Above Atmospheric Pressure

When the stuffing box pressure is below atmospheric pressure, a lantern ring is employed and lubricationis injected into the stuffing box (Fig. 7). A bypass line from the pump discharge to the lantern ring

connection is normally used providing the pumped liquid is dean.

Fig. 7 Typical Stuffing Box Arrangement when Stuffing Box Pressure is Below Atmospheric Pressure

When pumping slurries or abrasive liquids, it is necessary to inject a dean lubricating liquid from anexternal source into the lantern ring (Fig. 8). A flow of from .2 to .5 gpm is desirable and a valve andflowmeter should be used for accurate control. The seal water pressure should be from 10 to 15 psiabove the stuffing box pressure, and anything above this will only add to packing wear. The lantern ring Isnormally located In the center of the stuffing box. However, for extremely thick slurries like paper stock, itis recommended that the lantern ring be located at the stuffing box throat to prevent stock from

contaminating the packing.



Fig. 8 Typical Stuffing Box Arrangement when Pumping Slurries

The gland shown in Figures 5 through 8 is a quench type gland. Water, oil, or other fluids can be injectedinto the gland to remove heat from the shaft, thus limiting heat transfer to the bearing frame. This permitsthe operating temperature of the pump to be higher than the limits of the bearing and lubricant design.The same quench gland can be used to prevent the escape of a toxic or volatile liquid into the air aroundthe pump. This is called a smothering gland, with an external liquid simply flushing away the undesirableleakage to a sewer or waste receiver.

Today, however, stringent emission standards limit use of packing to non-hazardous water based liquids.This, plus a desire to reduce maintenance costs, has increased preference for mechanical seals.

Mechanical Seals A mechanical seal is a sealing device which forms a running seal between rotating and stationary parts.They were developed to overcome the disadvantages of compression packing. Leakage can be reducedto a level meeting environmental standards of government regulating agencies and maintenance costs

can be lower. Advantages of mechanical seals over conventional packing are as follows:

1. Zero or limited leakage of product (meet emission regulations.)2. Reduced friction and power loss.3. Elimination of shaft or sleeve wear.4. Reduced maintenance costs.5. Ability to seal higher pressures and more corrosive environments.6. The wide variety of designs allows use of mechanical seals in almost all pump applications.

The Basic Mechanical Seal All mechanical seals are constructed of three basic sets of parts as shown in Fig. 9:

1. A set of primary seal faces: one rotary and one stationary?shown in Fig. 9 as seal ring and insert.

2. A set of secondary seals known as shaft packings and insert mountings such as 0-rings, wedgesand V-rings.

3. Mechanical seal hardware including gland rings, collars, compression rings, pins, springs andbellows.



Fig. 9 A Simple Mechcanical Seal

How A Mechanical Seal Works

The primary seal is achieved by two very flat, lapped faces which create a difficult leakage pathperpendicular to the shaft. Rubbing contact between these two flat mating surfaces minimizes leakage. As in all seals, one face is held stationary in a housing and the other face is fixed to, and rotates with, theshaft. One of the faces is usually a non-galling material such as carbon-graphite. The other is usually arelatively hard material like silicon-carbide. Dissimilar materials are usually used for the stationary insertand the rotating seal ring face in order to prevent adhesion of the two faces. The softer face usually hasthe smaller mating surface and is commonly called the wear nose.

There are four main sealing points within an end face mechanical seal (Fig. 10). The primary seal is at theseal face, Point A. The leakage path at Point B is blocked by either an 0-ring, a V-ring or a wedge.Leakage paths at Points C and D are blocked by gaskets or 0-rings.



Fig. 10 Sealing Points for Mechanical Seal

The faces in a typical mechanical seal are lubricated with a boundary layer of gas or liquid between thefaces. In designing seals for the desired leakage, seal life, and energy consumption, the designer mustconsider how the faces are to be lubricated and select from a number of modes of seal face lubrication.

To select the best seal design, it's necessary to know as much as possible about the operating conditionsand the product to be sealed. Complete information about the product and environment will allowselection of the best seal for the application.

Mechanical Seal Types Mechanical seals can be classified into several tvpes and arrangements:

PUSHER: Incorporate secondary seals that move axially along a shaft or sleeve to maintain contact at the sealfaces. This feature compensates for seal face wear and wobble due to misalignment. The pusher seals'advantage is that it's inexpensive and commercially available in a wide range of sizes and configurations.Its disadvantage is that ft's prone to secondary seal hang-up and fretting of the shaft or sleeve. Examplesare Dura RO and Crane Type 9T.

UNBALANCED: They are inexpensive, leak less, and are more stable when subjected to vibration, misalignment, andcavitation. The disadvantage is their relative low pressure limit. If the closing force exerted on the sealfaces exceeds the pressure limit, the lubricating film between the faces is squeezed out and the highlyloaded dry running seal fails. Examples are the Dura RO and Crane 9T.



CONVENTIONAL: Examples are the Dura RO and Crane Type 1 which require setting and alignment of the seal (single,double, tandem) on the shaft or sleeve of the pump. Although setting a mechanical seal is relatively

simple, today's emphasis on reducing maintenance costs has increased preference for cartridge seals.

NON-PUSHER: The non-pusher or bellows seal does not have to move along the shaft or sleeve to maintain seal facecontact, The main advantages are its ability to handle high and low temperature applications, and doesnot require a secondary seal (not prone to secondary seal hang-up). A disadvantage of this style seal isthat its thin bellows cross sections must be upgraded for use in corrosive environments Examples are

Dura CBR and Crane 215, and Sealol 680.

BALANCED: Balancing a mechanical seal involves a simple design change, which reduces the hydraulic forces actingto close the seal faces. Balanced seals have higher-pressure limits, lower seal face loading, and generateless heat. This makes them well suited to handle liquids with poor lubricity and high vapor pressures suchas light hydrocarbons. Examples are Dura CBR and PBR and Crane 98T and 215.



CARTRIDGE: Examples are Dura P-SO and Crane 1100 which have the mechanical seal premounted on a sleeve

including the gland and fit directly over the Model 3196 shaft or shaft sleeve (available single, double,

tandem). The major benefit, of course is no requirement for the usual seal setting measurements for their

installation. Cartridge seals lower maintenance costs and reduce seal setting errors

Mechanical Seal Arrangem ents SINGLE INSIDE: This is the most common type of mechanical seal. These seals are easily modified to accommodate sealflush plans and can be balanced to withstand high seal environment pressures. Recommended for relatively clear non-corrosive and corrosive liquids with satisfactory' lubricating properties where cost of operation does not exceed that of a double seal. Examples are Dura RO and CBR and Crane 9T and215. Reference Conventional Seal.

SINGLE OUTSIDE: If an extremely corrosive liquid has good lubricating properties, an outside seal offers an economicalalternative to the expensive metal required for an inside seal to resist corrosion. The disadvantage is thatit is exposed outside of the pump which makes it vulnerable to damage from impact and hydraulicpressure works to open the seal faces so they have low pressure limits (balanced or unbalanced).



DOUBLE (DUAL PRESSURIZED): This arrangement is recommended for liquids that are not compatible with a single mechanical seal (i.e.liquids that are toxic, hazardous [regulated by the EPA], have suspended abrasives, or corrosives whichrequire costly materials). The advantages of the double seal are that it can have five times the life of asingle seal in severe environments. Also, the metal inner seal parts are never exposed to the liquidproduct being pumped, so viscous, abrasive, or thermosetting liquids are easily sealed without a need for expensive metallurgy. In addition, recent testing has shown that double seal life is virtually unaffected byprocess upset conditions during pump operation. A significant advantage of using a double seal over asingle seal.

The final decision between choosing a double or single seal comes down to the initial cost to purchasethe seal, cost of operation of the seal, and environmental and user plant emission standards for leakagefrom seals. Examples are Dura double RO and X-200 and Crane double 811T.

DOUBLE GAS BARRIER (PRESSURIZED DUAL GAS): Very similar to cartridge double seals ... sealing involves an inert gas, like nitrogen, to act as a surfacelubricant and coolant in place of a liquid barrier system or external flush required with conventional or

cartridge double seals. This concept was developed because many barrier fluids commonly used withdouble seals can no longer be used due to new emission regulations. The gas barrier seal uses nitrogenor air as a harmless and inexpensive barrier fluid that helps prevent product emissions to the atmosphereand fully complies with emission regulations. The double gas barrier seal should be considered for use ontoxic or hazardous liquids that are regulated or in situations where increased reliability is the required onan application. Examples are Dura GB2OO, GF2OO, and Crane 2800.

TANDEM (DUAL UNPRESSURIZED): Due to health, safety, and environmental considerations, tandem

seals have been used for products such as vinyl chloride, carbon monoxide, light hydrocarbons, and a

wide range of other volatile, toxic, carcinogenic, or hazardous liquids.



Tandem seals eliminate icing and freezing of light hydrocarbons and other liquids which could fall below

the atmospheric freezing point of water in air (32? F or 0? C). {Typical buffer liquids in these applications

are ethylene glycol, methanol, and propanol.) A tandem also increases online reliability. If the primary

seal fails, the outboard seal can take over and function until maintenance of the equipment can be

scheduled. Examples are Dura TMB-73 and tandem PTO.

Mechanical Seal Selection The proper selection of a mechanical seal can be made only if the full operating conditions are known:

1. Liquid2. Pressure3. Temperature4. Characteristics of Liquid5. Reliability and Emission Concerns

1. Liquid: Identification of the exact liquid to be handled is the first step in seal selection. The metalparts must be corrosion resistant, usually steel, bronze, stainless steel, or Hastelloy. The matingfaces must also resist corrosion and wear. Carbon, ceramic, silicon carbide or tungsten carbide

may be considered. Stationary sealing members of Buna, EPR, Viton and Teflon are common.2. Pressure: The proper type of seal, balanced or unbalanced, is based on the pressure on the sealand on the seal size.

3. Temperature: In part, determines the use of the sealing members. Materials must be selected tohandle liquid temperature.

4. Characteristics of Liquid: Abrasive liquids create excessive wear and short seal life. Double sealsor clear liquid flushing from an external source allow the use of mechanical seals on these difficultliquids. On light hydrocarbons balanced seals are often used for longer seal life even thoughpressures are low.

5. Reliability and Emission Concerns: The seal type and arrangement selected must meet thedesired reliability and emission standards for the pump application. Double seals and double gasbarrier seals are becoming the seals of choice.

Seal Environment The number one cause of pump downtime is failure of the shaft seal. These failures are normally theresult of an unfavorable seal environment such as improper heat dissipation (cooling), poor lubrication of seal faces, or seals operating in liquids containing solids, air or vapors. To achieve maximum reliability of a seal application, proper choices of seal housings (standard bore stuffing box, large bore, or largetapered bore seal chamber) and seal environmental controls (CPI and API seal flush plans) must bemade.

STANDARD BORE STUFFING BOX COVER Designed thirty years ago specifically for packing. Also accommodates mechanical seals (clamped seatoutside seals and conventional double seals.)



CONVENTIONAL LARGE BORE SEAL CHAMBER Designed specifically for mechanical seals. Large bore provides Increased life of seals through improvedlubrication and cooling of faces. Seal environment should be controlled through use of CPI or API flushplans. Often available with internal bypass to provide circulation of liquid to faces without using externalflush. Ideal for conventional or cartridge single mechanical seals in conjunction with a flush and throatbushing in bottom of chamber. Also excellent for conventional or cartridge double or tandem seals.

LARGE BORE SEAL CHAMBERS Introduced in the mid-8o's, enlarged bore seal chambers with increased radial clearance between themechanical seal and seal chamber wall, provide better circulation of liquid to and from seal faces.Improved lubrication and heat removal (cooling) of seal faces extend seal life and lower maintenancecosts.

BigBoreTM Seal Chamber

TaperBoreTM Seal Chamber



Large Tapered Bore Seal Chambers Provide increased circulation of liquid at seal faces without use of external flush. Offers advantages of lower maintenance costs, elimination of tubing/piping, lower utility costs (associated with seal flushing)

and extended seal reliability. The tapered bore seal chamber is commonly available with ANSI chemicalpumps. API process pumps use conventional large bore seal chambers. Paper stock pumps use bothconventional large bore and large tapered bore seal chambers. Only tapered bore seal chambers withflow modifiers provide expected reliability on services with or without solids, air or vapors.

Conventional Tapered Bore Seal Chamber: Mechanical Seals Fal l When Sol ids or Vapors Am Present in Liquid Many users have applied the conventional tapered bore seal chamber to improve seal life on servicescontaining solids or vapors. Seals in this environment failed prematurely due to entrapped solids andvapors. Severe erosion of seal and pump parts, damaged seal faces and dry running were the result.

Modified Tapered Bore Seal Chamber with Axial Ribs: Good fo r Serv ices Conta in ing Air , Min imum Sol ids This type of seal chamber will provide better seal life when air or vapors are present in the liquid. Theaxial ribs prevent entrapment of vapors through.improved flow in the chamber. Dry running failures areeliminated. In addition, solids less than 1% are not a problem.

The new flow pattern, however, still places the seal in the path of solids/liquid flow. The consequence onservices with significant solids (greater than 1%) is solids packing the seal spring or bellows, solidsimpingement on seal faces and ultimate seal failure.



Goulds Standard TaperBoreTM PLUS Seal Chamber: The Best Solution for Services Containing Sol ids and Air or Vapors To eliminate seal failures on services containing vapors as well as solids, the flow pattern must directsolids away from the mechanical seal, and purge air and vapors. Goulds Standard TaperBoreTM PLUScompletely reconfigures the flow in the seal chamber with the result that seal failures due to solids are

eliminated. Air and vapors are efficiently removed eliminating dry run failures. Extended seal and pumplife with lower maintenance costs are the results.

Goulds TaperBoreTM

Plus: How It Works The unique flow path created by the Vane Particle Elector directs solids away from the mechanical seal,not at the seal as with other tapered bore designs. And the amount of solids entering the bore isminimized. Air and vapors are also efficiently removed. On services with or without solids, air or vapors,Goulds TaperBore

TMPLUS is the effective solution for extended seal and pump life and lower

maintenance costs.

1. Solids/liquid mixture flows toward mechanical seal/seal chamber.2. Turbulent zone. Some solids continue to flow toward shaft. Other solids are forced back out by

centrifugal force (generated by back pump-out vanes).

3. Clean liquid continues to move toward mechanical seal faces. Solids, air, vapors flow away fromseal.

4. Low pressure zone create by Vane Particle Ejector. Solids, air, vapor liquid mixture exit sealchamber bore.

5. Flow in TaperBoreTM

PLUS seal chamber assures efficient heat removal (cooling) and lubrication.Seal face heat is dissipated. Seal faces are continuously flushed with clean liquid.



Stuf f ing Box Cover and Seal Chamber Guide

The selection guide on this page and the Seal Chamber Guide are designed to assist selection of theproper seal housing for a pump application.

JACKETED STUFFING BOX COVER Designed to maintain proper temperature control (heating or cooling) of seal environment. (Jacketedcovers do not help lower seal face temperatures to any significant degree). Good for high temperatureservices that require use of a conventional double seal or single seal with a flush and API or CPI plan 21.

http://www.gouldspumps.com/download_files/pump_fundamentals/sect_b4a_fig29.stm






JACKETED LARGE BORE SEAL CHAMBER Maintains proper temperature control (heating or cooling) of sea environment with improved lubrication of

seal faces. Ideal for controlling temperature for services such as molten sulfur and polymerizing liquids.Excellent for high temperature services that require use of conventional or cartridge single mechanicalseals with flush and throat bushing in bottom of seal chamber. Also, great for conventional or cartridgedouble or tandem seals.

Stuffing Box and Seal Chamber Application Guide

Stuffing BoxCover/Seal Chamber

Application

Standard BoreStuffing Box Cover

Use for soft packing. Outside mechanicalseals. Double seals. Also, accommodatesother mechanical seals.

Jacketed Stuffing BoxCover

Same as above but also need to controltemperatures of liquid in seal area.

Conventional LargeBore

Use for all mechanical seal applicationswhere the seal environment requires use of CPI or API seal flush pans. Cannot be usedwith outside type mechanical seals.

Jacketed Large Bore Same as Large Bore but also need tocontrol temperature of liquid in seal area.

Tapered Large Borewith Axial Ribs

Clean services that require use of singlemechanical seals. Can also be used withcartridge double seals. Also, effective onservices with light solids up to 1% by weight.Paper stock to 1% by weight.

Tapered Large Borewith Patented VaneParticle Ejector (AlloyConstruction)

Services with light to moderate solids up to

10% by weight. Paper stock to 5% byweight. Ideal for single mechanical seals. Noflush required. Also, accommodates doubleseals. Cannot be used with outsidemechanical seals.



Envi ronmenta l Contro ls Environmental controls are necessary for reliable performance of a mechanical seal on manyapplications. Goulds Pumps and the seal vendors offer a variety of arrangements to combat theseproblems.

1. Corrosion

2. Temperature Control3. Dirty or incompatible environmentsCORROSION Corrosion can be controlled by selecting seal materials that are not attacked by the pumpage. When thisis difficult, external fluid injection of a non-corrosive chemical to lubricate the seal is possible. Single or double seals could be used, depending on if the customer can stand delusion of his product.

TEMPERATURE CONTROL As the seal rotates, the faces are in contact. This generates heat and if this heat is not removed, thetemperature in the stuffing box or seal chamber can increase and cause sealing problems. A simple by-pass of product over the seal faces will remove the heat generated by the seal (Fig. 25). For higher temperature services, by-pass of product through a cooler may be required to cool the seal sufficiently(Fig. 26). External cooling fluid injection can also be used.

DIRTY or INCOMPATIBLE ENVIRONMENTS Mechanical seals do not normally function well on liquids which contain solids or can solidify on contactwith the atmosphere. Here, by-pass flush through a filter, a cyclone separator or a strainer are methods of providing a clean fluid to lubricate seal faces. Strainers are effective for particles larger than the openingson a 40 mesh screen. Cyclone separators are effective on solids 10 micron or more in diameter, if theyhave a specific gravity of 2.7 and the pump develops a differential pressure of 30-40 psi. Filters areavailable to remove solids 2 microns and larger.



If external flush with clean liquid is available, this is the most fail proof system. Lip seal or restrictingbushings are available to control flow of injected fluid to flows as low as 1/8 GPM. Quench type glandsare used on fluids which tend to crystallize on exposure to air. Water or steam is put through this gland towash away any build up. Other systems are available as required by the service.

API and CPI Plans

API and CPI mechanical seal flush plans are commonly used with API and CPI process pumps. Thegeneral arrangement of the plans are similar regardless of the designation whether API or CPI. Thedifference between the flush plans is the construction which provides applicable pressure-temperaturecapability for each type of pump. API plans have higher pressure and temperature capability than CPIplans. Each plan helps provide critical lubrication and cooling of seal faces to maximize seal reliability.

seal off centrifugal pump problems and seal basic selection.docx

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