PUMP MAGAZINE: Questions and Answers (61-70)


Question #61 Dear  Sir,


I am very much impressed with the kind of information you are providing. I want to know more about handling abrasive & corrosive liquids like Soap, Surfactants or Resins. I understand that the running the pump at slow speed would be a good option. Is it true that Positive Displacement Lobe pump is a better option? Can you throw more light on this? It would be very helpful for me.


Thank you.



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 cut 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 #1 is 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.





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 article, as well as in About Us general 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 grades of 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, cooling and 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 motor 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 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.



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.


  1. What is Sigma Phase in steels?


  1. 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?


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



Thanks & Best Regards

S. Jayakanthan

Quality Assurance

Dresser 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 and toughness 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 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 Technology
ITT 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 Robert’s question. Surprisingly, even well qualified pump professionals could not comment on this item, due to apparent unfamiliarity with this technology. Yet, once 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 Fisher and 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 our pump, 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:

 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. This causes 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 the wastewater 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 don’t 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 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 Bowser

Smith & 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 this section, as such feedback becomes available to us. Let us hear your view on this important subject.


Pump Magazine


Dear Dr. Nelik


I thank you and Mr. Hart for the subject well explained in Article #18

I also do agree that the Equipment Reliability is responsibility of multi-disciplined team which should make formalized approach covering:


 1) Selection of equipment (effective design, maintainability, life cycle cost effectiveness)

 2) Installation

 3) Operational approach, monitoring (parameters to be monitored, how to monitor, and assessment of values in view of reliability followed by cost effective remedial measure)

 4) Maintenance - applicable maintenance strategy, benchmarking, inventory control and all other associated activities. To have an effective functioning of such team, a leader is required. My personal view is Maintenance should be the leader. This is because the definition of Maintenance, in my view, is: “A conjunction of administrative and technical actions, which are required to revive an 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.




Sourav Kumar Chatterjee

Manager Rotating Equipment

HPCL, 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?



Dwajan, Power Plant, India 


     Answer: Dear Dwajan:

There are two ways to reduce pump flow: either by throttling of a discharge valve, or by changing a speed by a speed controller, such as VFD. The first method is inefficient but simple. When changing a pump speed – flow, head and power change in accordance with affinity laws: flow changes in direct proportion to speed, head as a square of speed, and power as cube of speed.


You need to construct a pump curve and a system curve, and see where these intersect – that would be your operating point. System curve should account for friction losses as well as static head. You should do that at several speeds to make sure you always have enough pump head to overcome system resistance.


Take a look at several other questions and articles that we have at various 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, you might be wasting a lot of energy, and should consider a new impeller, designed for lower flow, so that its BEP point is hydraulically shifted. We can provide such analysis for your pump and system if you like.



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 in which we get water is approx. two hundred feet plus (200'+) deep. The pump that is there has the Goulds name on it and as near as I can tell is what is known as a reciprocating pump. It has an electric motor mounted on top of it (which may or may not be the way it was meant to operate). There are varies lengths of wooden rods to get to water, each rod has metal ends with male or female treads that are riveted to the wood. My question is this can you tell me the era of this pump, its worth (it does work every well), the operation 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 Abel



          Answer:  Dear Stephanie,

It sounds like you have a relic. Don’t 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!).


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 get it 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!



Dr. Lev Nelik, P.E.

Pumping Machinery


     We have also obtained additional feedback from Goulds Pumps Marketing group, Water Systems Division. George Strally kindly provided this note:


Dear Stephanie,


The Goulds pump you describe is a very old "working head" or "pump head" with a pump cylinder, a.k.a., a working barrel in the water.  The rods transmit energy to the pump cylinder.  Many of this style pump were operated by windmills, tractor power take-offs and steam or gasoline engines. They were produced from the late 1800's until the 1940's when they were displaced by electric motor driven submersible pumps.


The pump cylinder has packings and check valves to allow water into the cylinder and to keep water from flowing back into the well when the piston is stroked up and down via the rods. This up and down movement of the cylinder is a positive displacement pump, basically, each stroke of the piston moves a volume of water up a distance equal to the volume (length) of the stroke.  We have had no parts available for this style pump since the 1940's or maybe 1950'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 which I can e-mail but I can mail or fax copies of old catalog pages if you desire.  A model number or pattern number from the pump would be helpful, for a 200' well my guess is a 1454 or 1518 from a 1910 catalog.


I have no idea of its value.  If someone has a need for water in an area where there is no electric service it would be more valuable than where there is power available.  I have attached a brochure showing our most popular 4" diameter submersible pump series, the GS as well as some technical data and Installation manuals for submersibles and storage tanks. They all open with Acrobat Reader. We suggest you contact a local Goulds Pumps dealer through the Yellow Pages or website for first hand assistance.  Goulds Pumps sells only through the Professional Sales Channel. See: www.goulds.com. for a dealer locator and product information.


Regards and Good Luck,


George Strally

ITT Goulds Pump, Water Systems Division




Question #69 Saludos Dr. Pump,


Me podria explicar el punto 5.1.10 de las normas API 610 referente al NPSHR.



            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 10th Edition 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 #70


I have a query on pump curves. We have a Sulzer multi-stage centrifugal pump. I'm trying to determine the performance of the pump using the pump curve provided by the manufacturer. Unfortunately, based on my calculations, the pump head and the flow rate do not fit with the curve. I have taken into consideration the 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 this difference? In actual performance I'm getting 325 m3/hr but based on the curve it should be about 375 m3/hr.


FYI, based on information 7 years ago and comparing the discharge pressure and flow rate, I'm able to get this same numbers currently, but how come with the calculation method I'm not able to do so. On the other hand, with respect to instrumentation calibration, they are fairly accurate: may be the pressure reading could be about 0.2 to 0.3 bar difference while the flow rate could be off by about 10m3/hr.


Could it be that the curve provided by the manufacturer is based on test conditions and could not be applied in actual conditions?


Look forward to hear from you.





Answer: Mike, - pump manufacturers usually test centrifugal pumps on water, and this is what curves reflect. If you are pumping cold water, you should get roughly the same results. Use our SEARCH function 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 out first. If still trouble, we may need to take a closer look at you curves, data, gage locations, etc.



Dr. Lev Nelik, P.E., Apics


Pumping Machinery


Follow-up question: Dr. Nelik,


I would like to clarify for the condensate pump suction side, would we need to consider the ambient pressure then start deducting off the elbow friction loss, but add the static height and not forgetting to deduct the vapour pressure. Here at the hot well/condenser it's a closed vessel. Is this the right approach? At present I have not taken into account ambient pressure at suction side.







NPSHA means net positive suction head available. It is sometimes confusing. The word "net" is meant to imply the suction head "above" the vapor pressure (expressed in feet (or meters if in metric units)). What matters to the pump is what goes on right at the inlet. Say you have a vessel with 20 feet of water above the impeller (fist stage if vertical multistage pump) centerline. Say the 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 not finished yet). Now - the flow flows from the tank to the pump. Say the friction losses (elbows, bends, filters, valves, etc.) amount to 10 feet of hydraulic losses. Now you got 54 - 10 = 44 feet left. Next - what is vapor pressure? For cold water, it is usually 0.34 psi, 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 on its water surface is not 34 feet, but something less - say it is only 5 feet.


Then, NPSHA = 20 + 5 - 10 - 0.8 = 14.2 feet


Now, say your condensate is not cold, but at about 200 deg.F. At that temperature the vapor pressure is higher then for cold water. Say the hot water vapor pressure is 4 psia (or about 9 feet) (I am just guessing at numbers here, but you should use real values). Now you subtract these 9 feet, which will leave you with less NPSHA then 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.



Lev Nelik


Hello Dr. Nelik,

Thanks for the reply. Gets my understanding clearer.






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