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PUMP MAGAZINE: QuestionsandAnswers (61-70)

Question #61 Dear Sir,I am very much impressed with the kind of information you areproviding. I want to know more about handling abrasive & corrosiveliquids like Soap, Surfactants or Resins. I understand that the

running the pump at slow speed would be a good option. Is it truethat Positive Displacement Lobe pump is a better option? Can youthrow more light on this? It would be very helpful for me.Thank you.Regards,Rakesh Gupta

Answer: Dear Rakesh,

Generally, Positive Displacement pumps are used for viscous fluids (over approximately

500 cP viscosity), and centrifugals are for low viscosity, although there is an overlapping

region, and occasional exceptions to the rule. When abrasives are present things

become more difficult, and wear is the main issue. You are very much correct by thinking

that slower speed may help. As a rule of thumb, the wear rate is reduced at slower speed,

and is a function of approximately RPM3(cubed). This is why a larger size pump, running

slower, is often selected when solids are present.

Gear pumps traditionally have not been a good selection for the abrasive pumpages,

because their bearings (bushings) are typically in the pumpage and are product-lubricated thus wear out fast if abrasives are present. Gears are used for two purposes:

to pump the fluid (transfer it from inlet to discharge ports), as well as to transmit torque: a

drive gear actually turns the driven (called idler).

Lobe pumps are close cousins of gear pumps, but the difference is that the lobes do not

actually touch, and torque transmission is done by another set of gears, called timing

gears, which are positioned outside pumpage, on the other side of the seals. Thus, the

job of the lobes is only to transfer fluid. Because if the fact that lobes do not touch they,

in theory, last longer. Incidentally, the non-contacting nature of lobes is also the reason

why they are used for food applications, and lobe pumps are often FDA and 3-A

approved.

However, their bushings, just like in gear pumps, are product lubricated, and will wear

out, or get plugged up by solids, similarly to any other pump type that has bushings in

the pumpage.

A more common pump types, used for solids handling are Progressing Cavity or

Peristaltic (Hose), although Hose pumps may not be good for sharp solids (hose gets cu


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up), but very good for softer solids, even at very high concentration.

When you have a combination of high viscosity and abrasives, Progressing Cavity

pumps could be a good candidates, as long as the temperature is reasonable (200-250

deg. F max. usually). In your case, resins can be pumped well with PC pumps. The

disadvantage of PC pumps is size they get to be rather long and take space, but if you

have floor room, then not an issue. As a rule of thumb, sizing of a PC pump is 75 psi per

stage.

If you have a specific application data, feel free to enter it via Application Help section of

our Pump Magazine, and we will assist with forwarding it to a qualified pump distributor.

For example, a Pumping Solutions company, sells Allweiler Progressing Cavity pumps,

that have an added feature of special stator design, allowing higher differential pressure,

thus reducing the overall pump size, and increasing its reliability. We will forward your

note to them for information and feedback. They handle US sales, as well as international

installations.

I hope this helps,

Dr. Lev Nelik, P.E.

Pumping Machinery

Question #62: Hello,

Article #1is touching on some interesting points. I find special interest in the second part

- talking about recirculation at low flow.

I will be grateful for some leads to more information explaining the mechanism of this

phenomenon, it's maintenance aspects, ways to discover and assure that this is the main

cause.

I am a mechanical engineer working at a Power Plant and currently trying to understand

and solve repeating frequent maintenance problems (many years old) of Vertical Heater

Drain Pumps.

Sincerely,

Marchel

Answer: Dear Marchel, -

We would be glad to help you with your problems, as we often see similar issues at

power plants. One approach is to apply Simsite composite material design impeller, with

rings and bushings, - with hydraulics specifically fine-tuned for the current operating

conditions. You might have seen the description of this approach in our recent Editorial
http://pump-magazine.com/pump_magazine/specifications/specifications.htmhttp://pump-magazine.com/articles/articles_summary.htm


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article, as well as in About Usgeneral section.

To start, could you send us some more information about your pump: perhaps a

sectional drawing, and a performance curve, which should have H-Q information, as well

as NPSH, and efficiency lines. We will need these data to evaluate design parameters,

such as suction specific speed, recirculation onset parameter, etc., and come with

correct hydraulics. We could then help produce the impeller in simsite composite

material. With 80% lighter then metal, rated to 400 deg. F (and higher with special gradesof simsite), and with tensile strength approaching steel you will have a much more

reliable retrofitted pump. Simsite engineered composites are significantly better then

metals from the cavitation standpoint, as well as handle to 15% abrasive particulates.

Plus, once we optimize the hydraulics, you will see significant efficiency improvements

i.e. significant energy savings.

We apply this technique for many power plants, as well as chemical plants (excellent

resistance to chemicals), paper mills, and refineries. Also, marine and navy pumps are

another examples of benefits of composites, since their superior resistance to salt water,

brine and brackish water, made them a material of choice for water intake pumps, coolingand recirculating pumps, screen wash, and similar.

Looking forward to hear from you,

Best regards,

Dr. Lev Nelik, P.E.

Pumping Machinery

Question #63 Dear Sir,

Is it possible to operate one pump in full flow and another one partially using variable

frequency drive in parallel operations?

Thank you,

Nagesh Kumar

NPC Company

Answer: Two pumps running in parallel do not have to be identical, but the rules

constructing the resulting combined curve will still apply. When one of the pumps is

controlled by the VFD, its head-capacity curve slides up or down depending on the moto

speed, which is changed by the VFD. The combined curve would need to be constructed

for a series of such speeds, and the intersection of each combined curve (at various

speeds) with the system curve will give you the operating point.

You can find more information on the parallel operation via SEARCH function. Some of
http://pump-magazine.com/about_us/about_us.htm


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the examples are Articles #8, #13, etc. Pumping Machinery also offers a consulting

service to perform this, and similar engineering requests. We would need to get some

more details regarding your applications to do that.

Regards,

Dr. Lev Nelik, P.E.

Pumping Machinery

Question #64 Dear Sir

I am from a valve manufacturing company. I need to clarify the following:

1. Whether pre-heating is required for Austenitic Stainless steels. During TIG it is possible but during

gas welding I think without preheating it is not possible to weld. Am I correct? Please explain.

2. What is Sigma Phase in steels?

3. For CA15M (410) casting, if I want to achieve 40 HRC - the heat treatment practice as per standards

is Astonishing the steel to 100 deg Centigrade followed by tempering at a temperature of 300-400

deg Centigrade. But our supplier has given same astonishing temperature but tempering

temperature of around 600 deg Centigrade to achieve the hardness valve of 40 HRC. Is it correct?

4. Will double tempering reduce the hardness for the above said material?

Thanks & Best Regards

S. Jayakanthan

Quality AssuranceDresser Valve India Pvt Ltd

We asked our contributor, Stephen Morrow, who is a Global Manager of Materials Technology at ITT Industries to

comment:

1) You never preheat an austenitic stainless steel - heating sensitizes it and temperature

controls are aimed at minimizing heat effects.

2) Sigma phase is formed between temperature range of 1050F and 1700F and is a brittle

phase of iron-chromium-nickel-molybdenum intermetallics that reduce ductility andtoughness in a material. It is a brittle intermetallic phase that forms in high chromium

stainless alloys.

3) Heat treaters are responsible for meeting hardness requirements - the correct word is

austenitizing. Hardness is controlled by tempering after austentization to achieve desired

final hardness.

4) Yes - double tempering will reduce hardness. See ASTM A487 temper requirements for


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CA6NM which calls for double temper at 1250F, then final temper at 1100F.

As a suggestion, I would recommend a reference book on basic metallurgy. Good start

could be ASM handbooks, and a copy of ASM Heat Treaters Guide for heat treatment

practices.

Stephen J. Morrow

Global Manager of Materials TechnologyITT Industries

Industrial Pump Group

Question #65 Dear Dr. Pump

We are using Smith and Loveless vacuum primed centrifugal pumps in our influent lift

station. We are experiencing a problem with the vacuum priming system water level. On

pump startup water enters a sensing dome and totally fills it. On pump shutdown this

dome stays full of water. On the next pumping cycle, the vacuum pump motors over for a

short burst and draws water into the vacuum systems line. On each successive cycle

water is drawn further up the lines until the total vacuum system is full.

In normal operation the water would only rise a small amount into the sensing dome

since the sensor probe protrudes down into the volute. On completion of pumping cycle

the water would receed into the volute. On next cycle this would repeat. The water level

would only increase as the sensing probe became dirty and would not sense liquid at the

bottom point of the probe. Thus it gave you time in between senor cleanings.

This problem has been occurring since the last upgrade to this station and the increase

in pump size and discharge quantity.

We have replaced all fittings, tubing, valves and vacuum pumps with no success. Since

these sensing probes are located in the low pressure zone of the pumps, could these

pumps be too large for the application? We have been in touch with the manufacturer

and their local repair service has worked on the system but neither has an answer or fix

to the problem.

Thank you,

Robert L. Challender, Sr.

From the Editor:The vacuum primed applications are rather specialized field in the pump

world. Editorial Board had some trouble locating a qualified expert to assist with the

answer to Roberts question. Surprisingly, even well qualified pump professionals could

not comment on this item, due to apparent unfamiliarity with this technology. Yet, once


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we finally got the answer, it became apparent that this method can be applied effectively

to many other applications, even outside the traditional waste treatment segment, if

proper familiarity and explanation of this technology is presented to the users.

Our search finally ended right where it should have started at the Applications

Department of Smith & Loveless Company, a manufacturer of these systems. Dan Fisherand Karen Bowser, both from Smith & Loveless not only provided an answer and pointed

to potential pitfalls, but they also provided a picture of a system, with a brief explanation

of its operating principle, so that other pump users would benefit from understanding the

concept.

Dan Fisher and Karen Bowser (Smith & Loveless Inc.) comment:

Smith & Loveless falls into the water/wastewater segment; this is our sole area of

concentration. However, within that segment Smith & Loveless has enjoyed a strong

reputation with respect to its centrifugal pump design and innovation. In addition to ourpump, our founders keenly recognized the need for packaged lift stations in wastewater

systems, and thus pioneered the factory-built pump station concept. Later developments

included the above-grade pump station concept with vacuum-primed wastewater pumps

Let me offer a brief overview of the kind of pump (station) we have been discussing and

the use of vacuum-priming used in these applications. Mr. Challender is referring to what

is called a Wet Well Mounted Pump Station, which is a lift station containing two to four

vertically mounted centrifugal, solids-handling pumps (designed exclusively for domestic

sewage). The station base resides above grade, mounted on top of the sewage wet well.

All of the pumps, controls, piping and valves also reside above grade and outside of the

corrosive wet well, maintaining a safe and clean environment for routine maintenance

and inspection. The centrifugal wastewater pumps operate by suction lift or what is

called "vacuum-priming".

The Vacuum Priming System is a simple process that includes just three basic

components: a prime sensor, a solenoid valve, and a vacuum pump, with spare parts

replacement kits similar to shown below:


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When the wet well level rises to certain point, the pumps are automatically started (Step

1). If the pump is not already primed, it will require the following two steps.

Step 2

When Step 1 occurs and the prime sensor indicates the pump requires priming, the

vacuum pump comes on and the solenoid valve opens. The vacuum pump evacuates air

from the pump suction line and the pump through the 3/8" diameter vacuum tubing. Thiscauses wastewater to fill the pump volute, cover the seal faces and prime the pump.

Step 3

When the prime sensor indicates the pump is primed, the solenoid valve closes, the

vacuum pump shuts off and the pump turns on. This is all done in a few moments, simply

and reliably. From a totally non-primed condition, the system is designed to prime the

pump in about 60 seconds under standard rated conditions. Once the pump is primed, it

is designed to stay primed indefinitely.

We call it vacuum priming because it uses a small vacuum pump to assist in priming thewastewater pump. Remember, this station sits several feet above the fluid level and thus

requires assistance when the pump needs to be primed. That's it. As such, the valve

components do require a simple periodic inspection or touch up cleaning.

We thank you for contacting us and allowing us to contribute to your online publication.

For more information on above grade wastewater pump stations, we invite you to visit

our Formula X(tm) Wet Well Mounted Pump Station website.

Possible reasons for the encountered problem:

We dont know the age or the sizing of the pumps but there are certain items that need to

be checked. To start, Mr. Challender mentioned a recent upgrade to the pump. Assuming

that they used Smith and Loveless components, the upgrade should not have caused the

problem. An increase in pressure (TDH) could magnify an existing problem, but again,

should not be the source of the problem.

Mr. Challender also mentioned that they had changed many of the components, but have

they simply tested for a vacuum leak? An easy way to do this is apply a generous amount
http://www.smithandloveless.com/FormulaX.htm


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of shaving cream to all of the connection points while the vacuum pumps are running.

Any vacuum leak will be immediately visible, and the connection can be easily repaired.

The next step would be to clean the electrode (sensor probe), but we got the impression that they are

cleaning the electrode on a regular basis. The only other component that needs regular attention is the

solenoid valve. Any debris in the seat of the solenoid may cause a leak. The stem of the valve needs to be

removed and the seat cleaned and inspected. Any wear of the seat would indicate a need to replace the

solenoid.

The next item is not a part of routine maintenance, but could be a solution. The electrode

relay in the panel may be contributing to the problem. Knowing the age of this system

would help, but we currently have a much improved electrode relay. That kit is available

from the Smith & Loveless Parts department. This department can be contacted directly

at 800-922-9048.

I hope that this is of some help, and I would invite Mr. Challender to contact the factory

directly if additional assistance is needed.

Dan Fisher and Karen BowserSmith & Loveless Inc.

Question (and comment) #66

These comments and a question came from our reader in response to a

recent article by Bob Hart (Pump Reliability What Does this Term

Mean to You?, Article #18 posted in section Technical Articles).

We will post additional feedback from other readers in thissection, as such feedback becomes available to us. Let us hear your

view on this important subject.

Editor

Pump Magazine

Dear Dr. NelikI thank you and Mr. Hart for the subject well explained in Article

#18

I also do agree that the Equipment Reliability is responsibility ofmulti-disciplined team which should make formalized approachcovering:1) Selection of equipment (effective design, maintainability, life

cycle cost effectiveness)2) Installation3) Operational approach, monitoring (parameters to be monitored,how to monitor, and assessment of values in view of reliability


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followed by cost effective remedial measure)

4) Maintenance - applicable maintenance strategy, benchmarking,inventory control and all other associated activities. To have aneffective functioning of such team, a leader is required. Mypersonal view is Maintenance should be the leader. This is becausethe definition of Maintenance, in my view, is: A conjunction ofadministrative and technical actions, which are required to revivean item or keep an item in a state at which it can provide desired

service as expected by user.I would like you to comment on this.Regards,Sourav Kumar ChatterjeeManager Rotating EquipmentHPCL, Mumbai, India

Question #67 Dear Sir,

The 33 TPh, 63 ata boiler is having a Boiler feed pump of capacity 41 TPH and 92

ata. It is a directly coupled pump to 200 kW Induction motor. The output is being

throttled with a control valve and for lower flow the water being recirculated

through Deaerator. The pressure drop across the pump is 25 ata. And there is

minimum of 9 ata pressure drop across the control valve due to valve design.

My question is:

a) Providing Variable speed drive (VFD) would be appropriate for the system to

save energy? Whether the control valve to be retained or suitably modified.

b) At lower load i.e. during start up the water feeding to the boiler is low,

hence recirculation would be more. Will the VFD will take care of the for low flow

requirement?

Regards,

Dwajan, Power Plant, India

Answer: Dear Dwajan:There are two ways to reduce pump flow: either by throttling of adischarge valve, or by changing a speed by a speed controller, suchas VFD. The first method is inefficient but simple. When changing apump speed flow, head and power change in accordance withaffinity laws: flow changes in direct proportion to speed, head asa square of speed, and power as cube of speed.You need to construct a pump curve and a system curve, and seewhere these intersect that would be your operating point. System


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curve should account for friction losses as well as static head.You should do that at several speeds to make sure you always haveenough pump head to overcome system resistance.Take a look at several other questions and articles that we have atvarious sections within Pump Magazine using Search function.If you find that you are using less flow then required, and always

bypass, then even a VFD may not be the answer. In such case, youmight be wasting a lot of energy, and should consider a newimpeller, designed for lower flow, so that its BEP point ishydraulically shifted. We can provide such analysis for your pumpand system if you like.Regards,Dr. Lev Nelik, P.E.Pumping Machinery

Question #68 Dr. Pump,I just recently purchased an old cabin in the mountains of PA. The well inwhich we get water is approx. two hundred feet plus (200'+) deep. Thepump that is there has the Goulds name on it and as near as I can tell is whatis known as a reciprocating pump. It has an electric motor mounted on top ofit (which may or may not be the way it was meant to operate). There arevaries lengths of wooden rods to get to water, each rod has metal ends withmale or female treads that are riveted to the wood. My question is this canyou tell me the era of this pump, its worth (it does work every well), theoperation of it, how to maintain it, and what I could replace it with if I would

need to? I thank you in advance for a quick and timely response.Stephanie AbelPennsylvania

Answer: Dear Stephanie,

It sounds like you have a relic. Dont laugh! some people actually collect really

old pumps, and in my own days at Goulds in Seneca Falls I recall we had an old

Goulds pump mounted at the corporate lobby, displaying it proudly to the visitors.

Some of these old pumps are still installed and work. I doubt, however, you will

find any spare parts, and would need to buy a more modern pump from Goulds

and any other pump company that sells deep well pumps, - or work with your local

mechanic that takes it as a personal hobby to play with antiques. The wooden

rods, for example, is clearly something dating way back. You may want to note the

serial number, pump model, and any other information you may still have with a

pump or any manuals that miraculously might still be at the attic. (Unfortunately,

sometimes it is only possible when the pump is actually pulled up), and which time

the installer is already working on a new pump for you!).


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What I suggest you do is this: look up a local pump distributor in your Yellow

Pages. Pump wells is a big thing in Pennsylvania, and you should be able to find

one easily, - there should be several listed for your area. They will ask you the

well size and how much water is there. They will then quote you a deep well

pump, with a motor. They normally also install it. The whole thing should cost you,

as a guess, between $500 and $1,000.

But do not let go your old pump! Goulds marketing people might be willing to getit from you for their promotionals, and the next thing you know you will inherit

a small fortune from Goulds! You never know: you might have struck oil even

with a water well!

Regards,

Dr. Lev Nelik, P.E.

Pumping Machinery

We have also obtained additional feedback from Goulds Pumps

Marketing group, Water Systems Division. George Strally kindlyprovided this note:Dear Stephanie,The Goulds pump you describe is a very old "working head" or "pumphead" with a pump cylinder, a.k.a., a working barrel in the water.The rods transmit energy to the pump cylinder. Many of this stylepump were operated by windmills, tractor power take-offs and steamor gasoline engines. They were produced from the late 1800's until

the 1940's when they were displaced by electric motor drivensubmersible pumps.The pump cylinder has packings and check valves to allow water intothe cylinder and to keep water from flowing back into the well whenthe piston is stroked up and down via the rods. This up and downmovement of the cylinder is a positive displacement pump,basically, each stroke of the piston moves a volume of water up adistance equal to the volume (length) of the stroke. We have hadno parts available for this style pump since the 1940's or maybe1950's. I just completed 31 years of employment at Goulds Pumps

and I have seen them only in old catalogs and service manuals.Unfortunately, we have no electronic files for the old pumps whichI can e-mail but I can mail or fax copies of old catalog pages ifyou desire. A model number or pattern number from the pump wouldbe helpful, for a 200' well my guess is a 1454 or 1518 from a 1910catalog.I have no idea of its value. If someone has a need for water in anarea where there is no electric service it would be more valuablethan where there is power available. I have attached a brochureshowing our most popular 4" diameter submersible pump series, the


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GS as well as some technical data and Installation manuals forsubmersibles and storage tanks. They all open with Acrobat Reader.We suggest you contact a local Goulds Pumps dealer through theYellow Pages or website for first hand assistance. Goulds Pumpssells only through the Professional Sales Channel. See:www.goulds.com. for a dealer locator and product information.Regards and Good Luck,

George StrallyITT Goulds Pump, Water Systems Division

Question #69 Saludos Dr. Pump,Me podria explicar el punto 5.1.10 de las normas API 610 referenteal NPSHR.

PEDRO TOLEDO

Answer: Dear Pedro, -

Unfortunately my Spanish is not good. I think your question relates to NPSHR as

addressed by the API specification. Which API Edition do you have? The latest is 9th,

although most people still use 8th. Actually, the 10thEdition is being released as we

speak.

I also recommend you use SEARCH function on our web, and search for words like

NPSH, Cavitation, Suction, etc. you may find many references and explanations

that might explain your question.

Again, sorry for my Spanish language limitations.

Regards (Salutos!?),

Dr. Lev Nelik, P.E., Apics

Pumping Machinery

Question #70I have a query on pump curves. We have a Sulzer multi-stagecentrifugal pump. I'm trying to determine the performance of thepump using the pump curve provided by the manufacturer.Unfortunately, based on my calculations, the pump head and the flowrate do not fit with the curve. I have taken into consideration the


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velocity head, the friction losses and elevation head.Formula used: Total Head = Total Discharge Head - Suction Head.Is there something else I'm missing out that is showing thisdifference? In actual performance I'm getting 325 m3/hr but basedon the curve it should be about 375 m3/hr.

FYI, based on information 7 years ago and comparing the dischargepressure and flow rate, I'm able to get this same numberscurrently, but how come with the calculation method I'm not able todo so. On the other hand, with respect to instrumentationcalibration, they are fairly accurate: may be the pressure readingcould be about 0.2 to 0.3 bar difference while the flow rate couldbe off by about 10m3/hr.Could it be that the curve provided by the manufacturer is based ontest conditions and could not be applied in actual conditions?

Look forward to hear from you.Thanks,Michael

Answer: Mike, - pump manufacturers usually test centrifugal

pumps on water, and this is what curves reflect. If you are pumpingcold water, you should get roughly the same results. Use our SEARCHfunction and type in a key word such as "performance" or "curves"or "head" etc. - there are many articles and discussion topics that

would pop up which have to do with definitions. Check these outfirst. If still trouble, we may need to take a closer look at youcurves, data, gage locations, etc.Regards,Dr. Lev Nelik, P.E., ApicsPresidentPumping Machinery

Follow-up question: Dr. Nelik,

I would like to clarify for the condensate pump suction side, wouldwe need to consider the ambient pressure then start deducting offthe elbow friction loss, but add the static height and notforgetting to deduct the vapour pressure. Here at the hotwell/condenser it's a closed vessel. Is this the right approach? Atpresent I have not taken into account ambient pressure at suctionside.Thanks,Michael


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Mike,-

NPSHA means net positive suction head available. It is sometimesconfusing. The word "net" is meant to imply the suction head"above" the vapor pressure (expressed in feet (or meters if inmetric units)). What matters to the pump is what goes on right atthe inlet. Say you have a vessel with 20 feet of water above the

impeller (fist stage if vertical multistage pump) centerline. Saythe vessel is open to atmosphere, which is 14.7 psi or 34 feet. So- you have 20+34 = 54 feet suction head - so far (we are notfinished yet). Now - the flow flows from the tank to the pump. Saythe friction losses (elbows, bends, filters, valves, etc.) amountto 10 feet of hydraulic losses. Now you got 54 - 10 = 44 feet left.Next - what is vapor pressure? For cold water, it is usually 0.34psi, or about 0.8 feet.So now: NPSHA = 44 - 0.8 = 43.2 feet.

If your tank is closed and under some vacuum, then the pressure onits water surface is not 34 feet, but something less - say it isonly 5 feet.Then, NPSHA = 20 + 5 - 10 - 0.8 = 14.2 feetNow, say your condensate is not cold, but at about 200 deg.F. Atthat temperature the vapor pressure is higher then for cold water.Say the hot water vapor pressure is 4 psia (or about 9 feet) (I amjust guessing at numbers here, but you should use real values). Now

you subtract these 9 feet, which will leave you with less NPSHAthen if it was cold water. Also do not forget specific gravity(which may be less then 1.0 for hot water).I hope this helps.Regards,Lev Nelik

Hello Dr. Nelik,Thanks for the reply. Gets my understanding clearer.

Michael

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