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Pump FAQs Hydraulic Institute Pump FAQs®

Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs as a means of ensuring a healthy dialog on subjects of common technical concern. ANSI/HI Standards are adopted in the public interest and are designed to help eliminate misunderstandings between the manufacturer, the purchaser, and/or the user and to assist the purchaser in selecting and obtaining the proper product for a particular need.

As an ANSI approved standards developing organization, the Hydraulic Institute process of developing new standards or updating current standards requires balanced input from all members of the pump community. We invite your questions and will endeavor to provide answers based on existing ANSI/HI Standards and technical guidelines. Please direct your inquiries to: pumpquestions@pumps.org.

Use the linked table of contents below to browse our entire library of Pump FAQs® articles or use the Search facility at the left to query the whole website, including our extensive database of Pump Questions and Answers in the Pump FAQs® section.

1999-05:1
Our plant is operating pumps on cooling tower service which are experiencing cavitation damage to the cast iron impellers. Should there be cavitation damage in the pump impellers under these conditions?

1999-05:2
We operate a sanitary sewage pumping plant, which frequently creates vortices at the pump inlet pipes. The pumps are mounted in a dry pit. The vortices are reducing the pump flow and causing excessive vibration in the pumps. Increasing the liquid level over the pumps would be very expensive. What else can be done to eliminate the vortices?

1999-05:3
Some centrifugal pump manufacturers show a vertical dotted line on their pump rating curves with the notation “minimum allowable flow.” Is there a standard procedure for determining this limit? If not, what criteria are used to determine this value?

1999-09:1
Can we reduce the pump head on a multistage centrifugal pump by trimming only one or two impellers, and is it better to cut the impeller shrouds as well as the impeller vanes?

1999-09:2
How much air can a centrifugal pump handle, and what can be done to prevent airbinding?

1999-09:3
Can the NPSHR curve be extrapolated back to shut off in order to get this information?

1999-09:4
How closely must I align the pumps, and how do I measure the misalignment?

2000-01:1
In the HI Standard HI 9.8 – 1998 Pump Intake Design, page 12, Figure 9.8.10, can someone assume that the minimum can diameter is a can that accommodates the bowl outside diameter and then use that value as D₁? Is any credit given to low header and can velocities, say 2.0 fps, with respect to the 3.0D₁ dimension above the header? Is any credit given to the 3.0D₁ dimension if it is at the end of the header such that it turns up into the pump and no flow goes past the pump, similar to example 3 but without the turning vane elbow and with the bottom of the pump above the top of the header?

2000-01:2
I have a question regarding temperature rise in a closed system where a centrifugal pump is pumping water. Shall I use the inefficiency of the pump (pump input power minus pump output power) or the pump input power alone for determining the temperature rise in the water?

2000-01:3
With many different pump types available, and many manufacturers which produce them, how can a buyer best evaluate both pump type and supplier to decide what and who to buy from?

2000-02:1
How can I specify and purchase a pump so that its BEP will meet my operating conditions?

2000-02:2
I know that centrifugal pump hydraulic performance can be influenced by the design of the suction pipe, but what is the effect of the discharge pipe on hydraulic performance? I understand that high pockets can trap air, elbows on the pump suction produce uneven flow and small pipe and long length will reduce NPSHA. Do these factors affect the pump if on the discharge side?

2000-02:3
We are installing vertical turbine type pumps over an open well and a reinforced concrete floor will support the pump. What is the acceptable flatness tolerance for the floor to properly support the pump discharge head?

2000-03:1
I take issue with the second question in FAQs in the February 2000 issue. You state that valves, elbows or other fittings attached directly to the pump discharge port will not effect what happens inside the pump impeller and casing. Can you explain why?

2000-03:2
What makes a vertical pump a GOOD vertical pump? We use them for pumping liquids from one tank to another part of the plant.

2000-03:3
We have a new water system pump which operates with the excessive noise with smaller existing pumps. The noise sounds like the pump is handling sand. What is the cause of the noise, and can it be eliminated? After nine months of operation, examination shows no impeller damage.

2000-09:1
Our plant is operating a system with several centrifugal pumps in parallel that exhibits waterhammer problems when one of the pumps is shut down.

2000-09:2
Is there any guideline on the increase in vibration for multipump installations?

2000-09:3
Is there a design standard or good practice that will provide information on the maximum water velocity in the suction header?

2001-09:1
I know that pumps should not be subjected to excessive forces and moments from the system piping, but how do excessive forces damage the pump and what is the weakest link in this regard?

2001-09:2
Is it an acceptable practice to select centrifugal pumps at rates of flow that are less than 50% of the Best Efficiency Point (BEP) in order to get a pump, which requires lower values of Net Positive Suction Head Required (NPSHR)?

2001-09:3
When the centrifugal pump draws down the liquid level in the tank, a vortex forms in the liquid and air is drawn into the pump. How can this problem be corrected?

2001-12:1
I observed a vortex breaker design drawing in the November 2001 issue of FHS magazine. It was a baffle plate design (page 22). Is there a sample design layout for an alternative vortex breaker using a cross rather than a baffle plate?

2001-12:2
I have seen specifications for fire pump installations, which refer to NFPA-20. What other standard(s) may be used when specifying fire pumps?

2001-12:3
HI published a chart titled “Upper Limits of Specific Speeds”. Does HI have a current version of this chart? How is this figure adjusted for friction of the suction piping? Similarly, does a velocity head factor need to be applied as well?

2002-04:1
Isn’t it better to publish NPSHR curves with higher values based on 0% reduction in total head or zero cavitation?

2002-04:2
Our plant uses a 10-inch vertical turbine pump, which is about 30 feet long, to supply cooling water. The requirements have been changed and we need an increase in flow of about 10%. According to the pump rating curve, the pump should satisfy our needs, but it does not. We have renewed the impeller wearing ring clearances, but we cannot reach the rating curve performance. What else can be done? We cannot increase the impeller diameter due to power limitations.

2002-04:3
We have difficulty in getting wearing ring data for several older pumps. Is there a general guideline on recommended wearing ring clearance that we can use?

2002-07:1
Electric power generating stations sometimes use submergence control to maintain the proper rate of flow for condensate pumps. How does this work and is such practice detrimental to pump life?

2002-07:2
Normal pump operation will eventually corrode and erode the inside of a pump casing until the thickness of the casing wall is too thin for safe operation. How can this safe thickness be determined and what are the potential consequences of operating with less than proper thickness?

2002-07:3
We operate a vertical turbine type well pump that has a clutch at the top of the motor that often disengages when the pump starts. What causes this to happen and what can be done to prevent it?

2002-09:1
One of our utility pumps takes suction from a river that frequently becomes muddy. The bronze impeller and wearing rings become badly eroded more quickly than anticipated. What do you recommend to increase useful impeller life?

2002-09:2
We are operating an end suction pump with an elbow connected to the suction flange. The suction connection is eroded on one side due to the uneven flow coming out of the elbow. Is there a simple solution?.

2002-09:3
Is there an easy way to evaluate the viscosity value above which centrifugal pumps are not recommended?

2003-01:1
We have been operating an API 610 pump at 750⁰ F that is handling heat transfer fluid. The pump is experiencing excessive bearing failures, typically every 6 to 12 months. The bearings are well protected and properly lubricated, however the failures persist. What can be done to increase the Mean Time Between Failure?

2003-01:2
Our new paint production unit is having problems with mechanical seal leakage in the paint transfer pumps. These are ANSI B73.1 pumps and examination shows evidence of clogged recirculation lines to the seals and solidification of paint around the mechanical seal parts. Can you suggest any solutions?

2003-01:3
We are operating an older centrifugal pump with a non-existent address on the nameplate. How can I locate the supplier or manufacturer in order to obtain specific information on the pump and purchase replacement parts?

2004-01:1
We are operating a large (centrifugal) horizontal water pump that is taking suction from a lake which is six feet below the pump. After startup, the flow rate from the pump decreases slowly for several hours. If the pump is restarted, it again pumps at the full rate of flow. What can cause this and what can be done to correct the problem?

2004-01:2
After installing a new 20 hp pump, we checked its performance and found that the total head was ten percent low. The system-head curve was checked and determined to be as predicted. Before we contact the supplier, is there something we should check?

2004-03:1
When measuring vibration on vertical pumps, does the allowable vibration depend on the height of the motor, or on the height above the baseplate at which the readings are taken?

2004-03:2
I understand that the efficiency of variable speed drives is reduced as operating speed and power is reduced. Does this negate the power saving from the accompanying reduction in pump speed?

2004-03:3
I have read that inducers on the inlet to centrifugal pumps can reduce NPSH required by as much as 50 percent. Is this true? If so, how can this be?

2004-04:1
I understand the importance of monitoring pump performance in order to prevent unexpected pump failures. Performance parameters such as discharge pressure, rate of flow, input power, and vibration are straight forward. But how do we know when corrosion or erosion have reduced pump casing wall thickness to the point at which casing failure may occur?

2004-04:2
Pumps operating in wet pit applications often suffer from the accumulation of grit or other solid material which accumulates near the pump inlet. This requires draining of the pit or removal of the pump to remove the solids. Is there a better way?

2004-04:3
When pumping liquids with entrained solids, especially slurries, I understand that hard material for the impeller and casing is recommended to resist erosion. I also hear that soft rubbery material is also used. How can this be? When are rubbery materials best used?

2004-05:1
We are replacing a 30,000 gpm vertical pump with a larger one, and are concerned that the new pump will have enough submergence to prevent vortices at the pump inlet. What guidelines are available to determine if enough submergence is available?

2004-05:2
In applications on handling slurries, we find that for higher heads centrifugal pumps are limited in what they can do. Can reciprocating pumps be used in these applications? If so, are any special design changes necessary?

2004-05:3
On low NPSH available applications it is often necessary to apply a centrifugal pump at 50% of its design flow rate to get a pump with low NPSH required values. What is the downside of doing this?

2004-06:1
We are considering the use of a magnetic drive pump for handling toxic liquids. The containment shell between the inner and outer magnet assemblies is very thin. We have concerns about wear in the shell and leakage of the liquid. Is our concern valid, and what can be done to protect against leakage?

2004-06:2
I understand that there are cautions to be followed regarding motor starting torque during the start up of vertical turbine pumps. What is this all about? What can be done to avoid startup problems?

2004-06:3
Is there a simple guideline for allowable misalignment measurements?

2004-07:1
When installing a horizontal pump, is it better to grout the pump baseplate or let it float free?

2004-08:1
Can we add a second pump with a rate of flow of 50% of the existing pump, or must we replace the existing pump with a larger one?

2004-08:2
Can a typical centrifugal pump be used as a turbine, and if so, what precautions must be taken?

2004-08:3
What causes water hammer and what can be done to correct it?

2004-09:1
I understand that pipe strains are bad for pumps and inherently have this problem due to temperature changes which result in thermal expansion of the piping. Expansion joints are designed to relieve such forces, but what else can be done to solve this problem?

2004-09:2
Many sources, including the Hydraulic Institute e-learning program Centrifugal Pumps: Fundamentals, Design and Application, describe the use of Affinity Laws which are used to predict the performance of a centrifugal pump when the impeller diameter is reduced or cut down. One of the laws says that Q ₁/Q₂ = D₁/D₂, where Q is the rate of flow and D is the impeller diameter. However, ANSI/HI 1.6-2000 Centrifugal Pump Tests says that at a given speed, Q₁/Q₂ = (D₁/D₂)² (H₁/H₂)^0.5 which is equivalent to Q₁/Q₂ = (D₁/D₂)³. Which is correct, or is there some explanation for the difference?

2004-09:3
How do pump manufacturers determine the design rate of flow and total head for each pump in the series?

2004-10:1
I know that a centrifugal pump can overheat badly if run at shut off for some time, but how can I determine the minimum rate of flow through the pump to avoid excess temperature build up?

2004-10:2
I have heard that the rate of flow through centrifugal pumps can be regulated by submergence control instead of by throttling. How does this work, and does it cause damage to the pump?

2004-10:3
We are expanding our building, including the fire protection system. If the existing fire pump must be replaced, what special requirements must we look for in their replacement?

2004-11:1
The first answer in the September issue of Pumps and Systems says that spring mounted baseplates can also work well to avoid pipe strains on pumps. How can I know if the baseplate stiffness is sufficient to work without grouting?

2004-11:2
In our power plants we have several applications where we need to reduce the NPSH Required by the pumps by as much as fifty percent. Is this possible? If so, how can this be done?

2004-11:3
When starting our Vertical Turbine type well pump, the shaft will often rise up and disconnect the pump shaft from the motor. What can be done to prevent this from occurring?

2004-12:1
Five to ten diameters of straight pipe is usually required between the closest fitting and the pump. Is there a similar requirement for fittings such as elbows or valves on the discharge side of the pump?

2004-12:2
A question in the February 2004 issue of Pumps and Systems discussed the performance problem of a centrifugal pump when handing air or other gas. Do rotary pumps have a similar problem when pumping liquids with entrained air?

2004-12:3
What is the maximum temperature liquid that centrifugal pumps can handle? Are there any special requirements for a pump to do this?

2005-01:1
Our plant operates several pumps handling liquid with some solids. We know that flushing the seals is important, but how much flushing liquid is necessary?

2005-01:2
There is a pump room in our plant with six centrifugal pumps on different services. The noise from the pumps is loud and uncomfortable to people working on the pumps. Is this normal, and what if anything can be done to reduce the noise?

2005-01:3
We would like to check the hydraulic performance of several submersible sump pumps which are difficult to reach.

2005-02:1
How can the vertical condensate pumps on steam condensers in power generating stations operate with little or no NPSH available?

2005-02:2
We are having difficulty measuring the hydraulic performance of a reciprocating power pump due to the fluctuation in the rate of flow and discharge pressure caused by pulsations from each stroke of the pistons. What can be done to overcome this problem?

2005-02:3
With many different pump types available, and many manufacturers which produce them, how can we determine which pump is the most suitable for our application and will provide the best service at the lowest cost over the lifetime of its operation?

2005-03:1
We operate a small plant and would like to improve the reliability of our centrifugal pumps and minimize unplanned pump shutdowns. Can you suggest a plan for monitoring pump performance to achieve our goal?

2005-03:2
I understand that pump vibration is an important parameter in predicting the imminent failure of a pump. Is this true? How is the vibration level measured, and what is an acceptable level of vibration for ASME B73 Chemical pumps?

2005-03:3
We are having problems with corrosion when pumping sulfuric acid. What do you suggest as a practical solution for this problem?

2005-04:1
We operate a number of end suction centrifugal pumps on a chemical process application. The seals operate well, but the anti-friction bearings fail in less than twelve months. Is this normal? If not, what can be done to increase bearing life?

2005-04:2
I have been told that reciprocating pumps must be protected against operation with a closed discharge valve, but that is not necessary with air operated diaphragm pumps. Is this true and why?

2005-04:3
The December 2004 issue of P&S included a question and answer on air entrainment in rotary pumps which I found to be useful. Is there similar information on rotary pumps handling liquid with solids or slurries?

2005-05:1
We are operating an end suction centrifugal pump which takes suction from the bottom of an open tank. As the level in the tank drops, a vortex is formed which allows air into the pump. This changes the performance of the pump and upsets the process downstream. I understand that this can be corrected with baffle plates. Are there any guidelines in this regard?

2005-05:2
Our plant has a horizontal axially split case pump handling cooling water and the horizontal suction pipe includes a ninety degree elbow at the suction flange of the pump. The pump operation is noisy and one side of the impeller shows cavitation damage and the other side does not. I believe that the elbow on the suction is the major cause of the problem, but adding straight pipe in between is not practical. Is there another solution to this problem?

2005-05:3
I know that centrifugal pumps do not operate well on viscous liquids and rotary pumps are often recommended, but what about reciprocating pumps? Are there any limits to the viscosity of liquids that can be handled by reciprocating pumps?

2005-06:1
We use several metering pumps in our blending operation and are concerned about their accuracy. How accurate are these pumps and does accuracy change with different conditions?

2005-06:2
I have been told that centrifugal pumps require more NPSH margin at higher elevations, such as Denver, than at sea level. Is this true?

2005-06:3
The FAQ in the February 2004 issue of P&S showed the performance curve of a centrifugal pump when handling entrained air. Do self priming pumps perform the same way when pumping liquid with entrained air, or can they do better?

2005-07:1
We are designing a circular sump for the installation of three sewage pumps. Because of local restrictions on the size, we are concerned that the pump intake structure may not provide a good hydraulic design and are considering whether to build and test of a model of the intake. How do we select the appropriate rate of flow for the model test?

2005-07:2
During the maintenance of centrifugal pumps, how much wear of the wearing rings is considered normal, and what is the normal wearing ring clearance for a new pump?

2005-07:3
When checking the performance of a new centrifugal pump, the plot of the resulting head versus rate of flow curve appears to be lower than the manufacturer’s rating curve. How much deviation from the manufacturer’s rating curve is normal?

2005-08:1
When purchasing pumps for water supply systems, is there a simple way to determine the maximum allowable speed for a specific application? If so, what factors should be considered?

2005-08:2
We are operating storm sewage pumps which are normally oversized until it rains. They are quite noisy when operating at low rates of flow. Is this normal and can the noise contribute to pump damage? If so, what can be done to correct the situation?

2005-08:3
We are designing the sump for several vertical turbine pumps taking water through a pipe from a river. Is there any guideline for the minimum size of such a pump?

2005-09:1
How can we get longer life from the ball bearings in our pump? Our process uses an end suction centrifugal pump to circulate heat transfer liquid at 750 degrees F. The bearing housing is cooled, and the bearings look clean after they fail. What else should we look for?

2005-09:2
Non-metallic materials such as Noryl and Teflon have excellent corrosion resistance and should be good for pump components. However, they probably have limitations due to tensile strength and temperature. If so, what are these limits?

2005-09:3
I have been told that centrifugal pumps handling hydrocarbon liquids can operate safely with less NPSH Available than the NPSH Required by the pump rating curve. Is this true? If so, how much reduction in the NPSHR can be allowed?

2005-10:1
With the ever increasing cost of oil and resulting increases in the cost of power, what can be done to decrease the operating cost of existing pump systems?

2005-10:2
We are converting several vertical turbine pumps to the submersible type. Are there any special installation requirements that we should be aware of?

2005-10:3
What special design features should we look for when purchasing non-clog pumps for wastewater service?

2005-11:1
What can be done to increase the life of bearings in both canned motor pumps and magnetic drive pumps? Bearings are a primary cause of failure in such pumps, and any improvement in life is important.

2005-11:2
What is the physical meaning of an impeller’s specific speed? What are its units of measurement? How is this related to the pump’s operating speed? Is there a preferred value for specific speed?

2005-11:3
What is an ANSI pump?

2005-12:1
How can I determine the lift capability of a centrifugal pump?

2005-12:2
Our small plant is close to a dam which has a steady rate of flow over it. Is it practical to install a vertical turbine pump as a turbine and connect the electrical power that is generated to our normal power supply? Are there any special control problems?

2005-12:3
What are the consequences of excessive nozzle loads, and how can allowable nozzle loads be determined?

2006-01:1
With so much emphasis on power savings how can we know what can reasonably be expected as good efficiency from our centrifugal pumps? We have looked at the published efficiency of some suppliers pumps, but they vary considerably.

2006-01:2
What are “ booster pumps” and where are they used? Are there any special requirements for such applications?

2006-01:3
Is torsional critical speed the same as pump critical speed? If not, please explain the difference.

2006-02:1
We are operating an end suction pump under suction lift conditions and it sounds like it is pumping gravel. Can we check the NPSH capability of this pump by test, and if so, what is the test procedure?

2006-02:2
Which type of balance is recommended for centrifugal pump impellers, and what is the acceptable limit of unbalance for an impeller?

2006-02:3
Why are some pumps hydraulically operated when the more simple mechanical drive is available?

2006-03:1
What is a “can” pump? I have seen this term applied to both centrifugal and vertical turbine pumps(VTP). Will you please explain it for me?

2006-03:2
We installed three new vertical turbine pumps, which at first exceeded the specification limits for vibration. This was corrected by adding shims between the pump discharge head and the foundation. Should this be necessary on a new installation, or shouldn’t the pump and foundation match better to avoid the use of shims?

2006-03:3
We are using a large number of air-operated reciprocating pumps and are concerned about the amount of power that they are using. How can we check the efficiency of these pumps?

2006-04:1
We need to replace several pumps handling paper stock, and need to know what special problems we should look out for. Can you help with such information?

2006-04:2
What is a balancing disc or drum?

2006-04:3
Maintenance of pumps is a costly operation in our plant. Are there any secrets to reducing these costs?

2006-05:1
We operate about one thousand centrifugal pumps and find that ball bearing failure is a major cause of pump shutdown which requires repair, and sometimes causes unscheduled system shutdown. How can we monitor these pumps to eliminate or predict these failures?

2006-05:2
What is reverse runaway speed? What is the cause? Is it dangerous and can it be prevented?

2006-05:3
How does a change in liquid viscosity effect the performance of a rotary pump? I have seen a viscosity correction graph for the performance of centrifugal pumps but nothing for rotary pumps.

2006-06:1
We recently rebuilt a vertical turbine pump with new impellers and wearing rings and tested its performance. The pump is handling water at ambient temperature (S=1.0). However, the result showed total head performance which was lower than the published curve as the rate of flow was increased. The pump is thirty feet long so we put a test gage two pipe diameters downstream of the discharge elbow. The shut off head nearly matches the published curve. Do you have any suggestion for increasing the pump head?

2006-06:2
I understand that NPSHR (required) by a pump is measured by the manufacturer using cold water, and I do not find information on how to correct this for other liquids. Hydrocarbons, for example, have a wide range of specific gravities and vapor pressures which must affect the NPSHR performance of a pump. Is this true?

2006-06:3
When very large pumps, both high rate of flow and high horsepower are custom built, a smaller model may be built and tested to prove the proper performance of the design. What are the rules for building such a model?

2006-07:1
I have been told that the performance characteristics of centrifugal pumps are changed when pumping viscous liquids such as hydrocarbons. How can this performance change be calculated?

2006-07:2
What is an API pump? I assume it is related to pumps used in the petroleum industry, but what is special about it?

2006-07:3
We recently experienced line shaft failure in a multistage vertical turbine pump with ten-inch diameter bowls. An analysis of the break pointed to torsional fatigue as the cause but the pump was operating under full load in a steady mode and vibration monitors did not show excessive vibration. How can the shaft fail in fatigue under these conditions?

2006-08:1
Some centrifugal pump manufacturers show NPSHR curves that increase in value at rates of flow below the best efficiency point (BEP), while others show a continuing decrease. Why is this? Is there a difference in design?

2006-08:2
We are considering the purchase of several vertical turbine pumps and do not know whether to specify an open or enclosed lineshaft. Can you suggest any guidelines to help in making this determination?

2006-08:3
Some rotary positive displacement pumps apparently use timing gears on the end of the rotating elements to keep them synchronized while others do not. Why is this? What are the criteria that dictate their use?

2006-09:1
We operate about one thousand centrifugal pumps and find that ball bearing failure is a major cause of pump shutdown which requires repair, and sometimes causes unscheduled system shutdown. How can we monitor these pumps to eliminate or predict these failures?

2006-09:2
We are considering the addition of a centrifugal pump in series with an existing pump to increase output. What are the potential problems of this and what guidance can you provide?

2006-09:3
When starting and/or stopping centrifugal pumps, what procedure is best to follow? Should the valves be open or closed and if so in what sequence?

2006-10:1
Due to a recent thrust bearing failure in one of our deep well pumps, we would like to determine the down thrust on the bearing from the pump. Is there a simple way of calculating this?

2006-10:2
I keep hearing about suction recirculation but cannot find a good explanation. Can you help me?

2006-10:3
Pumps designed to handle chemicals are usually made of corrosion resistant materials, but I need to know if there are any other requirements necessary for chemical applications?

2006-11:1
I know that water hammer can do substantial damage to pumps and piping. What can be done to remove this threat?

2006-11:2
I have seen vertical turbine pumps that are built with vertical hollow shaft motors and others with vertical solid shaft motors. What factors would lead to one design or the other?

2006-11:3
Mechanical seal failure represents most of the causes for pump repair in our plant, with unscheduled shutdown and loss of production. What can be done to relieve this problem?

2006-12:1
I know that slurries require special attention when being pumped. What characteristics of slurries should be given consideration when specifying a rotodynamic pump?

2006-12:2
When pumping volatile liquids, such as solvents and some petroleum products, will the vapors cause any problems with vapor binding or insufficient NPSH available?

2006-12:3
Some pump instructions refer to non-Newtonian liquids. What does this mean?

2007-01:1
I have been told that centrifugal pump impellers may still cavitate when operating with NPSH Available greater than NPSH Required. Is this true? If so, why do pump suppliers show NPSHR values when they know that cavitation may occur?

2007-01:2
What is pump critical speed and how is it determined? I understand that operation at critical speed could damage the pump.

2007-01:3
Is there a preferred sequence for starting reciprocating power pumps, and if so please describe it?

2007-02:2
How do I evaluate the capability of a pump on a given system to know if it is capable of withstanding the expected forces and moments from pipe strains?

2007-02:3
What is the limit of the amount of air or gas that can be entrained in the liquid that is being pumped and what is the affect of the gas? What can be done to increase the allowable limit?

2007-03:3
What are the most commonly used methods for priming a pump?

2007-04:3
What is the most practical way to measure the vibration level of canned motor and magnetic drive pumps?

2007-05:1
Q. What is a steam pump? How does it work and where is it used? A. Properly called a “Direct Acting Steam Pump”, it is a reciprocating (steam) engine and a pump

2007-05:2
Is there a guideline for decontamination of pump parts when it is necessary to send them out for repair? We operate a chemical plant with over 1000 pumps and often find this necessary.

2007-05:3
What should we look for when buying pumps for slurry applications? The literature is quite confusing with alternatives including hard metals of different types as well as soft elastomers.

2007-06:1
I understand that cavitation in impellers can still occur when NPSH Available is higher than NPSH Required. Many pumps apparently operate this way. What properties are important for when selecting cavitation resistant materials for impellers?

2007-06:2
What should we consider when selecting pumps for condensate service in electric power generating plants?

2007-07:1
Q. Rotary pumps are relatively simple and usually inexpensive. Where are they most frequently used, and why are they not more commonly used? A.

2007-07:2
Q. Rotary pumps are relatively simple and usually inexpensive. Where are they most frequently used, and why are they not more commonly used? A. Rotary pumps excel in applications with viscous liquids. There is no practical upper limit of

2007-08:1
Q. How is the maximum allowable working pressure of a centrifugal pump established? A. The maximum allowable working pressure (MAWP) of a centrifugal

2007-08:2
Q. Is there a way of predicting the maximum operating speed for a reciprocating plunger pump when pumping a viscous liquid? A. Yes,

2007-08:3
Q. What special requirements should we look for when ordering condenser circulating pumps for a large electric generating plant? A. Condenser circulating water pumps take cool water from a river, lake, stream or cooling tower basin and circulate it through the

2007-09:1
What are the most probable causes of insufficient discharge flow or pressure in centrifugal pumps?

2007-09:2
We have a 100 hp end suction pump that has a broken shaft. What are the causes of shaft breakage?

2007-09:3
What is an inducer and how does it work?

2007-10:1
Is it true that centrifugal pumps should be built with ball bearings that have greater than normal internal clearance?

2007-10:2
Q. I have read that pumps with high suction energy level are more susceptible to cavitation damage than low suction energy level. Is this true and how is high suction energy defined? A. Yes, pumps with high suction energy level are generally more likely to suff

2007-10:3
What is the purpose of putting vacuum valves or vacuum breakers in pump discharge piping? How does this affect the pump performance? The pump is handling ambient temperature water.

2007-11:1
We need to increase flow through our system and plan on adding a second pump in parallel to the existing pump. Are there any pitfalls in doing this and how can they be avoided?

2007-11:2
The shaft of our vertical turbine well pump sometimes rises up and disconnects from the top of the driver. What causes this and how can it be corrected?

2007-11:3
What is the best method for the measurement of rate of flow of viscous liquids?

2007-12:1
Many articles are being written about life cycle cost as applied to the purchase of pumps. How much of this information is also applicable to existing pump installations?

2007-12:2
How is the performance of air operated diaphragm pumps affected by the viscosity and specific gravity of the liquid?

2007-12:3
What is discharge recirculation and what damage does it do to pumps? Can changes to the pump be made to correct this problem?

2008-01:1
Most centrifugal pumps have a horsepower characteristic curve which rises as rate of flow increases to some level and then levels off or turns downward. However, other pumps have more level power curves or even some that are higher at low rate of low. Why is this, and can it be a problem?

2008-01:2
With the increasing emphasis on energy conservation, turbines are being installed on sources of hydraulic power that are normally wasted. Is it necessary to install small turbines in such cases or can centrifugal pumps running backwards be used?

2008-01:3
Is there a simple way to determine the minimum submergence required for a large vertical turbine pump to prevent the formation of surface vortices and the entrance of air into the pump?

2008-02:1
When a centrifugal pump impeller is reduced in diameter to reduced total head and rate of flow, the affinity rules predict that the new rate of flow is equal to the original rate of flow times the ratio of the new diameter to the old as in the equation Q₂= Q₁x D₂/D₁. On the other hand, if the model of a larger pump is made to a smaller size to facilitate testing, the rate of flow is predicted as the cube of the diameter ratio or Q₂= Q₁ x (D₂/D₁)³. Why are these two equations different?

2008-02:2
How do pump manufacturers decide what rate of flow and total head to use when designing pumps which are to be used in their standard product lines? Is there some logic and reasoning for this or is it based on demand?

2008-02:3
We are installing a multistage pump and plan on using a reduced voltage starter. Is this practical and what precautions should be taken?

2008-03:1
When installing a horizontal pump, is it better to grout the pump baseplate or let it float free? Different sources provide opposing views on this subject.

2008-03:2
I understand that the efficiency of variable speed drives is reduced as operating speed and power is reduced. Does this negate the power saving from the accompanying reduction in pump speed?

2008-04:1
We are operating a centrifugal pump and a recent change in the system has resulted in a deficiency of about five to ten percent in the rate of flow. Can anything be done to the pump to increase the flow to meet our needs?

2008-04:2
For slurry applications, we have observed that centrifugal pumps that develop higher heads are limited in their operation. Can reciprocating pumps be used in these applications? If so, are any special design features necessary to handle slurries?

2008-04:3
Pumps operating in wet pit applications often suffer from the accumulation of grit or other solid material which accumulates near the pump inlet. This requires draining of the pit or removal of the pump to remove the solids. Is there a better way?

2008-05:1
I have heard that the rate of flow through centrifugal pumps can be regulated by submergence control instead of by throttling the pump discharge. How does this work, and does it cause damage to the pump?

2008-05:2
I have an older pump with a pump model but an obsolete address on the nameplate. How can I locate the supplier in order to get information about the pump and purchase replacement parts?

2008-05:3
We are considering the use of a magnetic drive pump for handling toxic liquids. The containment shell between the inner and outer magnet assemblies is very thin. We have concerns about wear in the shell and leakage of the liquid. Is our concern valid, and what can be done to protect against leakage?

2008-06:1
I know that a centrifugal pump can overheat badly if run at shut off too long, but how can I determine the minimum rate of flow through the pump to avoid excess temperature build up?

2008-06:2
When measuring vibration on vertical pumps, does the allowable vibration depend on the height of the motor, or on the height above the baseplate at which the readings are taken?

2008-06:3
What is a Pitot Tube Pump?

2008-08:01
What is the maximum pumped liquid temperature that can be handled by an end suction centrifugal pump, and what must be done to a pump for it to operate successfully at that temperature?

2008-08:02
What is the effect of higher elevation above sea level on the NPSH required by a pump? For example does a pump require more NPSH in Denver than at sea level? If so, is there a simple way of correcting for this?

2008-08:03
What is “water hammer”, what causes it, and is it damaging to the pump or system?

2008-09:01
When operating centrifugal pumps on corrosive or erosive applications, how can the user determine when the casing wall is worn too thin for safe operation? What is the minimum safe operating wall thickness?

2008-09:02
What is the best way to avoid excessive pipe strains on a pump caused by expansion in piping due to temperature change? Are expansion joints a viable solution?

2008-09:03
In applications where NPSH available is low, it is often necessary to apply an oversized centrifugal pump that operates at 50 percent of its design flow rate to obtain a pump with low NPSH required values. What is the downside of doing this?

2008-10:01
What is a free standing baseplate and when should it be used? Are there any special design requirements?

2008-10:02
Do rotary pumps have the same problems as centrifugal pumps when pumping liquids with entrained air or gas?

2008-10:03
I understand that vertical can pumps can operate with very low values of NPSH available, such as on condensate service. What is a vertical can pump and how does it work with such low NPSHA?

2008-11:03
How can we determine how much flow a mechanical seal requires to provide adequate flushing?

2008-12:01
Our office building has a pump room in the basement, which causes sufficient noise to be bothersome to the people in the office above it. What can be done to reduce the noise?

2008-12:02
Can rotary type pumps be used to pump slurries? If so, are there any special cautions?

2008-3:3
After installing a new 20-hp centrifugal pump, we checked its performance and found that the total head was 10 percent below the guaranteed point. The system-head curve was checked and determined to be as predicted. Before we contact the supplier, is there something we should check?

2009-01:2
When installing a 15,000-gpm rotodynamic (vertical) pump, is there a method for determining the required submergence of the pump inlet opening below the water surface to prevent the formation of free surface vortices?

2009-01:3
What is the hydrocarbon correction for NPSH required by a centrifugal pump and what are the correction values?

2009-02:1
We are expanding some of our buildings and need to replace the existing fire pumps. What are the technical requirements for such pumps?

2009-02:2
Our plant operates a number of centrifugal pumps with ball bearings, and bearing failure is the most common cause of unscheduled pump shut down. What should be the average life of pump bearings and what can be done to improve it?

2009-02:3
What can be done to ensure better lubrication and increase the life of bearings in sealless pumps?

2009-03:1
Q. How can we tell if a pumping system is designed and operated properly? Some problems such as leaking seals are obvious, but should we watch for any other symptoms?

2009-04:1
We have recently installed several double suction between bearing pumps and would like to verify that their vibration levels are within acceptable limits. How should this be done, and what is an acceptable upper limit for such vibration?

2009-04:2
How can we determine the proper size for the intake sump to accommodate several vertical turbine pumps taking input from a river?

2009-04:3
What is the most effective way to reduce energy consumption in existing centrifugal pump installations?

2009-05:1
What can be done to avoid the high-pressure differential from rupturing the diaphragm in reciprocating diaphragm pumps?

2009-05:2
What are non-clog pumps, and what is unique about their design?

2009-05:3
Q. What can be done to ensure better lubrication and increase the life of bearings in sealless pumps?

2009-06:1
Q. What are the criteria for determining the maximum allowable forces and moments that can act on a centrifugal pump’s nozzles without damaging the pump? What part of a pump is most likely to be damaged by excessive forces and moments?

2009-06:2
Q. What are the most commonly used stainless steel alloys for pumping sulfuric acid?

2009-06-3
What design features should we look for in selecting a pump for handling paper stock?

2009-07:1
Simplicity and low cost make rotary pumps a good selection for some applications. Is there a simple guide to the maximum rate of flow and discharge pressure for which such pumps can be used?

2009-07:2
We are operating a large horizontal centrifugal pump lifting water from a lake, and the rate of flow gradually reduces with time. However, when the pump is restarted, the rate of flow returns to its original, normal value. What is the cause of this problem?

2009-07:3
Some engineers refer to ANSI pumps but whenever I conduct a web search on ANSI (American National Standards Institute) a list which is nearly 400 pages long is generated. What does this designation represent?

2009-08:1
What causes radial thrust on volute pump impellers? Should the pressure in the volute be uniform with proper design?

2009-08:2
What causes some vertical pumps to run backward when shut down, and can this be a problem?

2009-08:3
Besides varying pump speed, how can the flow rate from metering pumps be adjusted?

2009-09:1
When selecting a vertical turbine pump design, what factors should be considered when determining the use of open or enclosed lineshaft?

2009-09:2
Another alternative in determining vertical turbine pump design is solid versus hollow shaft motors. What are the considerations for making that selection?

2009-09:3
When installing submersible vertical turbine pumps, what driver characteristics must be considered?

2009-10:1
What is the definition of specific speed, to what does it pertain and how is it used?

2009-10:2
Our pump room has many different pumps that are all noisy when operating. Is this normal?

2009-11:1
What is an acceptable amount of residual unbalance in an impeller after it has been balanced?

2009-11:2
The corrosion resistance of polymer materials makes them good choices for many pump parts. However, lower temperature and pressure limits may be a concern. What are the normal temperature and pressure limits for polymers?

2009-11:3
Measurement of flow rate through reciprocating pumps is often difficult due to the pulsating flow. What method can provide accurate flow measurement for these pumps?

2010-01:1
We are buying a 1,000-hp rotodynamic (centrifugal) pump and are anxious to verify that it will perform in accordance with the manufacturer’s published rating curve. Can we expect that the pump will actually meet the performance that the published curve shows?

2010-01:2
When installing a 15,000-gpm rotodynamic (vertical) pump, is there a method for determining the required submergence of the pump inlet opening below the water surface to prevent the formation of free surface vortices?

2010-01:3
What is the hydrocarbon correction for NPSH required by a centrifugal pump and what are the correction values?

2010-02:1
We are expanding some of our buildings and need to replace the existing fire pumps. What are the technical requirements for such pumps?

2010-02:2
Our plant operates a number of centrifugal pumps with ball bearings, and bearing failure is the most common cause of unscheduled pump shutdown. What should be the average life of pump bearings and what can be done to improve it?

2010-02:3
How can the bathtub vortex at the bottom of a pump suction tank be eliminated as the liquid level is drawn down?

2010-03:1
How can we tell if a pumping system is designed and operated properly? Some problems such as leaking seals are obvious, but should we watch for any other symptoms?

2010-03:2
Higher pump speed usually results in lower pump cost and higher efficiency. How can I determine the maximum practical speed for any given application?

2010-03:3
With so much emphasis on power savings, how can we select pumps with reasonably high efficiency?

2010-04:1
We have recently installed several double suction between bearing pumps and would like to verify that their vibration levels are within acceptable limits. How should this be done, and what is an acceptable upper limit for such vibration?

2010-04:2
How can we determine the proper size for the intake sump to accommodate several vertical turbine pumps taking input from a river?

2010-04:3
What is the most effective way to reduce energy consumption in existing centrifugal pump installations?

2010-05:2
What are non-clog pumps, and what is unique about their design?

2010-05:3
What can be done to ensure better lubrication and increase the life of bearings in sealless pumps?

2010-06:01
How carefully must pump impellers be balanced to avoid unacceptable vibration levels when the pump is running?

2010-06:02
When purchasing rotodynamic pumps, how can we be assured of selecting pumps with the highest efficiency?

2010-06:03
What are “boiler feed booster pumps,” and why are they necessary?

2010-07:01
What determines the value of external forces and moments that can be applied to a pump without causing detrimental effects?

2010-07:02
What methods are recommended for determining the acceptable amount of leakage from an operating pump?

2010-07:03
We have a problem with the buildup of grit and other solids in our sewage pump sump that require frequent cleaning. What can be done to prevent this?