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Pumps by Ross Mackay, president, Ross Mackay Associates
Ross Mackay is president of Ross Mackay Associates Ltd., Aurora, Ontario, a firm he started in 1990 to provide training and consulting on pumps. Previously, he worked for 30 years for three major pump manufacturers. He speaks regularly on pump reliability and is the author of a new book, “The Practical Pumping Handbook.” He also has written “12 Steps to Mechanical Seal Reliability in Centrifugal Pumps.” More information on Mackay and his expertise on pumps can be found at www.practicalpumping.com.
Is dynamic balancing important?
I have always been told that dynamic balancing is not as critical on impellers because as soon as the impeller is loaded, the water causes hydraulic imbalance. We have always balanced them down to NEMA standards anyway, but it would be nice to know for sure.
Category: Pumps
Does the velocity in the suction line need to be maintained?
In a new installation, the supplier has erected a suction pipe of 3 inches connected to suction nozzle of 4 inches in the centrifugal pump for slurry application. The general engineering practice says the suction pipe should be the same or one size larger than the suction nozzle of the pump. As per supplier, this arrangement was made to maintain slurry speed of >1.5m/sec. With this condition, we are having frequent seal failures. Please suggest whether this type of suction pipe sizing is acceptable. And is it required to maintain slurry speed in the suction side as given by supplier?
Category: Pumps
What are the disadvantages of putting a strainer on the discharge of a pump?
What are the disadvantages of putting a strainer on the discharge of a pump?
Category: Pumps
What is causing the strainer to choke?
We have an ammonia recovery system at our ammonia plant. Ammonia is recovered in a scrubber operating at 105 Kg/cm2 with lean water. Water is pumped through a PD pump. Basket type strainer is installed at pump suction line in vertical position. Chocking problem is frequently observed with this strainer with algae layer due to which pump flow reduces to minimum. What do you recommend?
Category: Pumps
What are the limitations of centrifugal pumps?
I know positive displacement pumps deliver fixed flow with pressure affected by downstream piping system, but when we supply the suction of a screw rotary pump with a centrifugal pump in series arrangement, some doubt arises. What would be the effect of centrifugal discharge pressure injecting screw pump suction from the view of screw pump flow rate? By the way what is the minimum reasonable viscosity justifying the use of positive displacement pump?
Category: Pumps
Is it necessary to install an expansion joint at pump discharge piping?
Is it necessary to install an expansion joint at pump discharge piping? If so, where is the best location?
Category: Pumps
How best to install a Non-Return Valve
I am HoD mechanical at Uch Power Station-Pakistan. We have three cooling water pumps to circulate cooled water from cooling tower's cold water basin into steam turbine condenser and vice and versa. Each CW pump is a mixed flow centrifugal pump with 17280 m3M/Hr capacity; 495 RPM; 971 shaft power. Two pumps remain in service while one at stand-by. We have anti-reverse devices installed at each pump for reverse-flow protection. At pump discharge, we have a motor operated butterfly valve.
Problem:
We are experiencing too many failures of our anti-reverse devices. So we intend to install "Non-Return Valve" between pump discharge and discharge motor operated valve. It may be pertinent to highlight that our discharge line is of 72-inch diameter. Will it be practicable to install non-return valve at this bigger line? If so, could you share some detail about the type NRV suitable for our application and any other technical information?
Category: Pumps
What is a good arrangement from the pump discharge flange?
In centrifugal pumps that are pumping caustic or any acid, on the pump discharge line there is first NRV then pressure gauge along with drain point and after that an isolation valve. What is the reason for this arrangement?
Category: Pumps
Why does our new pump have a lower flow rate?
We replaced an old horizontal multi-stage pump with a new vertical multi-stage pump. The new pump should have more flow rate than the old pump, but that did not happen. Let me explain the specification below.
The old pump has piping details as such:
- Horizontal multi-stage pump with side suction.
- Gland packing seal
- Pump inlet-outlet = 2.5"-2.5"
- Piping installation for inlet-outlet = 3" - 3"
- There are three elbows used on the suction side as well as y-strainers, flexible joint and foot valve.
- Pipe length on the suction is approximately 5 meter (horizontal + vertical).
- Suction lift is approximately 1 meter to 2 meter measured from the suction flange to the surface of the water.
- Discharge piping is directly on top of the pump's discharge outlet.
- There are 3" NRV, gate valve, flexible joint on the discharge side.
The new pump has piping details as such:
- Vertical in-line multi-stage pump.
- Mechanical seal
- Pump inlet-outlet = 2"-2"
- Piping installation for inlet-outlet = 2" - 2"
- There are 1 elbows, 2" x 3" expander (so it can utilize the old 3" suction piping system), and foot valve on the suction side. Removed the old 3" NRV and flexible joint from the suction line.
- Pipe length on the suction is approximately 2.5 meter (horizontal + vertical).
- Suction lift is approximately 1 meter to 2 meter measured from the suction flange to the surface of the water.
- The discharge pipe is 2", goes straight for about 1 meter, then elbow upward to meet 2" x 2.5" concentric expander, after that connected to the old 3" fitting, valves and piping system.
Category: Pumps
What is the difference between vent and recirculation lines?
I see pumps used in ammonia storage (LPS) have both a vent line and minimum flow line. The vent line goes back to storage where the suction line came, but the minimum flow line returns to the storage top and also back to suction side of the pump. these lines?
Category: Pumps
Is there value to installing pump suction strainers?
Please inform about the design value of pump suction strainers. If the strainer is 10% clogged, then how much will the pumping flow be reduced?
Category: Pumps
How do we determine pump configuration?
In API 610, there are various types of pump-specific configurations -- BB1, BB5, OH2, etc. For boiler system, whereby there are various operating pressures (30 bars, 60 bars, and above 90 bars of condensate and feedwater), how do we determine which type of pump configuration is most suitable? What are the governing factors for pumps that are important to this specific application?
Category: Pumps
Why is an expander required on the discharge side of a pump?
1. Why is an expander required on the discharge side of a pump?
2. Why is the nonreturn valve (NRV) installed before the control valve in the pump discharge line? What will happen if we put the NRV after the control valve?
3. If we use an automatically operated valve in the pump discharge line, do we still have to install a NRV?
Category: Pumps
What is the reason behind multiple pumps discharging into a common header?
I saw three pumps connected in parallel discharging to a common header. The delivery of each pump is connected to the common header at some angle (lateral reducing tees). I just want to know the reason behind that. Moreover, I would like to know when a delivery of one pump is connected to another pump, the best way is using tees (at 90 degrees) or lateral tees (at some angle) assuming the outlet pipe after the tee connection is connected to a tank.
Category: Pumps
What is the best way to arrange a discharge header?
In the case of a discharge manifold of a system of pumps in parallel (a total of five centrifugal pumps in the present case), must the outlet piping to the process be positioned after the last pump or can it start immediately before the last pump? By adopting the last arrangement, would there be loss in the flow capacity, some turbulence, or even loss of energy or a possible unbalancing of one or more pumps?
Category: Pumps
What happens when two pumps lead into the same system?
What happens when we connect the discharge (A) of one pump (40MWC)to a discharge (B) of another(20MWC)without adding an expander and with adding an expander? Considering the discharge (B) is connected to an atmospheric tank. My doubt is will the discharge(B) flow toward the tank or toward the discharge(A) as (B) is of high pressure.
Category: Pumps
Can you offer best practices and guidelines for pump recirculation?
I have an application where the pump recirculation piping tie-in into the pump suction. If possible, I would like some best practices/guidelines to the following:
1. Temperature rise during circulation I have seen equations where calculations look at temperature increase when the pump is throttled. What is the calculation approach when the pump is in circulation to its suction? I have tried different approaches, e.g., one where I used the volume of the circuit and treated the calculation like heat input into a tank after a certain time period. The other approach is where I estimated the time a given molecule moves through the circuit before it enters the pump again. Both these approaches result in different times based on a given temperature rise. Please advise.
2. Also I would like to know guidelines/best practices on where to place the spillback return to the suction.
Category: Pumps
Why is there a difference in pump output?
Must the suction lines of parallel pumps be equidistant? In our plants (petrochemical), we normally have two pumps installed in parallel, one running and the other stand-by. Every 20 days we change the pumps (stop the one that is running and start the one that is in stand-by). During change of pumps, we do not have a problem, except with two pumps, which pump cyclohexane (cold) and there is not a equidistant arrangement between the suction lines of the pumps. But the problem is only with one of the pumps. For example, we have two pumps -- A and B. When A is running and we change to pump B, we do not have problem, but when are going to do the contrary, (Change B to A) we note a discharge pressure reduction.
Category: Pumps
What is each pump characterization curve used for?
There are three centrifugal pump characterization curves (H-Q) called flat, dropping and drooming type according to the change manner of discharge head with flowrate change. What are the service applications for each type? What is each characterization curve used for?
Category: Pumps
What pump is best to empty bulk containers?
We are planning to buy lubricating grease in bulk. How can we unload the grease from bulk containers? Would any proper pump help us? We can't melt the grease due to some degradation issues.
Category: Pumps
What is the power factor of VFD systems?
I am planning to replace a Variable Frequency Drive (VFD) electric motor instead of existing steam turbine to increase the pump speed by using a lower speed standard electric motor. I want to know whether I consider a separate additional horsepower in excess of pump brake horsepower due to using VFD motor or not. Suppose the pumping required power is a 100kw with the ordinary electric motor. If I decide to apply a VFD one for higher rpm, would the required power be the same as ordinary motor for VFD motor as well? If not, what is the power factor or efficiency of VFD systems?
Category: Pumps
How do you calculate the discharge head and suction head?
We have a 37 kw centrifugal pump that has the suction and discharge of 5 inches each. It is mainly used to lift the slurry (mixture of clay and water). The discharge rate at outlet is 80 cubic meters per hour. Please suggest how to calculate the discharge head and suction head?
Category: Pumps
How do you decide between steam or electrical turbines?
What are the main reasons for using turbine-driven pumps instead of electrical-motor driven ones --especially at not very high KW powers?
Category: Pumps
What's causing the pump to trip?
I have taken a pump with 2 m3/hour and 20 m head capacity. The suction pipeline size is 50 NB (2 inches) and discharge pipeline size is 40 NB (1 1/2 inches). The actual head at plant site is about 7 to 8 meters. But my pump is frequently tripping. Please provide a solution and suggest modifications.
Category: Pumps
How do you determine pump RPM?
I have always had the question about the main criterion determining the pump RPM. For instance, some pumps run at 2950 RPM while others may operate at 1490 RPM. What is the main factor for RPM selection of a pump -- particularly when we are faced with a vendor general chart recommending different pumps with different RPM for a specific H-Q service?
Category: Pumps
Should we correct the customer's pipe-size dimensions?
We have a problem on our pump suction line. Our client is providing 150NB pipe size, but our requirement flow needs nearly 250NB pipe size. Should we provide an expander? A 20m suction head is available.
Category: Pumps
Is there a distance limit on pump reducers and expanders?
At what distance shall the reducer/expander be situated in pump suction and discharge lines? Is there any specific distance limit on it from the specified nozzles based on the line sizes?
Category: Pumps
Can you suggest a good resource for pump selection, installation and replacement?
May I have a suggestion for a basic guide/resource to enable me have an excellent approach to addressing the required parameters for pump selection, installation and replacement specifically for process applications?
Category: Pumps
What is the material design for a bare shaft pump?
What is the typical material design for a bare shaft pump that does not make contact with liquid?
Category: Pumps
How do you correctly size piping leading to centrifugal pump?
Normally, the size discharge nozzle of pump is different with discharge piping size. It is always a bigger size. My understanding is that it depends on the design and flow delivery required. For example: nozzle discharge pump is 6" and discharge piping delivery is 12". How to put the best way for arrangement piping between 6" to 12". Whether bellow, non-return valve and other accessories can be match to 12" size or how?
Category: Pumps
Do I need to estimate the NPSHR for my pump supplier?
I am confused about NPSHR deliverable by pump manufacturers for a specific service. I know the required head and flow for the project pump. How can I guess the minimum NPSHR available that could be supplied for the project? The answer of this question leads to consider skirt height for the tower feeding the pump or not. In other words, I need to have NPSHR in advance for fixing NPSHR. Can I estimate typical NPSHR by having head and flow?
Category: Pumps
Can the suction size of the pump be bigger than the pipeline?
Pipe size is 12" and our suction pump size is 14". Are we allowed to connect this pipeline to the pump? Can the suction size of the pump be bigger than the pipeline?
Category: Pumps
Pumps: Finding The Correct Net Suction Pressure
I am balancing condenser water pumps for a major city.
The system is an open loop, with sump catch at the tower. It is approximately 15-feet down and 30-feet across. For the two pumps, required flow is 3400.
G.P.M max flow combined on pumps is 3900 G.P.M required net suction pressure is 4.2 across each pump and 1.90 at each suction diffuser, total= 12.2 N.S.P.
Correct gauge reading before pumps on suction full out is 5.2. G.P.M measured is 2700, sent N.S.P requirements in to design engineer who says we did not add into account atmospheric pressure and that is why we do not have the correct N.S.P. What of this atmospheric pressure shouldn't already be added into the gauge reading at the suction line? Is this an accurate statement by the design engineer?
Category: Pumps
How Many Pumps Should Pass Acceptance Test?
What percentage of 55 screw pumps in fuel-oil service should pass acceptance test?
Category: Pumps
What’s the right piping design?
What is the right size of the pipe between the suction and the discharge? We are using a 16-bar progressive screw pump. The size of the suction is an 8-inch diameter, but we reduced it to 4 inches and the discharge is reduced to 6 inches and we are pumping the heavy oil for about 750 meters away to the manifold. This tripped the motor and suddenly the pump damaged the stator. Do you think this piping design for this situation is right?
Category: Pumps
What's Causing The Pump To Trip?
We operate a pulverised fuel boiler and one of the requirements is for de-mineralized water to be pumped into the boiler continuously. As such, we have two pumps always running. The third pump (a standby pump) is always tripping when brought into service for when conditions are upset and there is a need to deliver extra boiler water to the boilers or when one of the running pumps is being maintained. This standby pump has been changed several times, aligned and still keeps tripping.
We are trying to troubleshoot to find out exactly what is causing this one pump alone to keep tripping while the other two are running well without tripping. Previously there were no tripping problems, but this has been happening now for the past few months going back to June 2008.
I need to investigate this problem and come up with a solution. What would you advise as the best way forward or as the best way to execute the troubleshoot. I am having meetings with the process engineers and process specialists so that I get more details of the operating conditions and so on.
My proposed plan of execution so far can be summarized as follows:
• Gather as much data as possible on the pump, motor, valves, NPSH, head, duty etc.
• Establish the operating conditions and the worst case scenarios when conditions are upset.
• Eliminate an electrical problem by having the electrical people do a thorough check on all the control systems and also by checking the motor and all its supporting accessories.
• If all electrical systems are checked and found to be working fine proceed as below.
• Do a design from first principles given the operating conditions.
• Compare the design and the current status on the pump vis a vis valves, manifold designs,
Would it be correct to assume that since these pumps have been operating without any problems for some time now up until this tripping problem started it is some parameter that has changed most recently and cannot be the design and layout?
Category: Pumps
Explaining the NPSH
Please explain the NPSH, much confused about this turm, also tell the uses of this and how to get that?
Category: Pumps
Deciding between screw-type pumps and centrifugal pumps
I am designing a pump with a flow rate of 6.5 m3/hr for two different grades of oil. The first type has a viscosity 200 cSt and is used for half of the year, while the second type has a viscosity of 25 cSt and is utilized during the second half of the year. I would prefer to have the same pump design for both grades of oils. Should I use a screw-type pump or a centrifugal pump?
Category: Pumps
Multi-stage pumps versus rotary pumps
When should you use a multi-stage pump instead of a rotary pump?
Category: Pumps
Quick questions about centrifugal pumps
Would you please answer the following questions:
1. How is the rotational speed and the impeller diameter of a centrifugal pump determined, and what is the effect of viscosity?
2. What is the maximum viscosity when using centrifugal pumps?
3. What are the applications of flat characterization and dropping curve centrifugal pumps?
Category: Pumps
Justifying minimum flow facilities
We are confronted with two different services pumps both using contineous minimum flow
1. Condensate pump from a vacuum surface condenser of a steam turbine
2. Lube oil pump also from a vacuum stripping tower
what are the main reasons justifying these minimum flow facilities on these pumps especially for the second one pumping high boiling point (low vapor pressure)?
Category: Pumps
What is the effect at the pump suction and discharge if the vacuum is raised?
We have a single stage centrifugal pump which is supplied by a 4 metre suction head drawn from a vessel that is under -70kPa of vacuum.
Pump NPSHR = 0.4 mtr
Process fluid = 46% Caustic in solution with Demineralised water
SP = 1.45
Viscosity = 1.37 cp
Fluid Temp = 115'C
Current Head = 23 mtrs
Current flow = 7.8 m3h @ 88% speed
Motor 2 pole with VSD
If the vacuum is raised to -80kPa what will be the effect at both the pump suction & discharge?
Category: Pumps
What is the optimal direction for the discharge nozzle to point on a centrifugal pump?
What is the optimal direction for the discharge nozzle to point on a centrifugal pump? We must install a 90 degree elbow immediately after the discharge if the discharge nozzle points straight up. Is there any loss of GPM or Head if the pump is rotated 90 degrees? Is a 3" discharge line too large for the pumps 1 1/2" discharge nozzle?
Category: Pumps
Diaphragm pump guidelines
I'm looking for some guidelines or reference for designing a diaphragm pump for Petrochemical usage.
Category: Pumps
Malfunctioning pump discharge valve
I work on an offshore oil production platform. Recently, we experienced a problem where an oil-to-shore pump (a centrifugal pump) was not moving liquid out through the discharge and pressure of the pump was higher than usual. What makes the situation more perplexing is that all the valves were lined up properly on the pump. Any explanations for this will be greatly appreciated.
Category: Pumps
Vertical pump installation
When installing a vertical pump, should the eccentric reducer on the discharge side of the pump be installed with the flat side on top?
Category: Pumps
Low-flow pump after repair
There are two magnetic-driven pumps in our hypochlorine unit. When we installed and started the pump for the first time, flow and pressure were good, but then the bush and sleeve broke, along with the thrust bearing, which are sic material. After repairing the pumps with new parts, they did not produce sufficient flow, but the discharge pressure was good and we checked the all parameters that can affect pump performance, including piping strain, piping restriction and alignment and vibration. There is no check valve on the discharge side and when we want to start the pumps and stop them, we close the valve on discharge side first and then open it to reach to operation condition. What is the reason for the low flow for this type of pump? What is the rule to use a check valve in centrifugal pumps if we did not install it? What is the rule for the internal clearance on the impeller side and also between bush and sleeve bearing on pump performance?
Category: Pumps
Impeller balance holes
What is the role of a balance hole in an impeller of a centrifugal pump — especially in magnetic driven centrifugal pumps? There are two magnetic driven centrifugal pumps together (main and its stand-by) in our plant, and one of the impellers has balance hole and the other does not. Should we drill-in the impeller without a balance hole to create it?
Category: Pumps
Stable pump flow
How can we estimate the minimum continuous stable flow for centrifugal pumps?
Category: Pumps
Design for two-phase flow of emulsion, gas line
How do you size a line for a two-phase flow of emulsion and produced gas? What is the best method to get accurate results? What should be the design criteria?
Category: Pumps
NPSH requirement
I have a pump that has a NPSH requirement of 2 m when it runs with water. I want to run condensate of a density of 700 kg/m3 and a viscosity of 0.53 cP. I recalculate the new NPSH available, but I wonder if the NPSH required stays the same?
Category: Pumps
Suction line size effect on pumps
What is the optimum ratio of eye size to suction line? I am considering a reducer from suction line to the size of eye. If the suction line is 1.5 times bigger than the eye, will it cause any decrease in the head of the pump?
Category: Pumps
Flow rate test data
I received the pump test bed data (flow rate, head and RPM Q-H curve). The test was conducted on cold conditions (i.e. at 28°C and 2,982 rpm). The vendor has converted the flow rate and head base on site conditions (i.e 135°C and 2,975 rpm) as follows. The flow rate was converted as 100.6 m3/hr x 2975/2982 = 100.4 m3/hr * 0.93 (i.e. specific gravity @ 135°C) = 93.3 tph and head was converted as 597.56 m x 2975/2982 = 594.76 m. Based on such converted flow rates and heads measured at different points during the test, the capacity Vs Head curve was prepared and declared to represent the conversion of head and flow rate to 135°C without taking any impact due to difference in density. Will this performance curve represent the flow and head at 135°C? If not, how should we can convert these parameters to 135°C for getting confirm that pump will able to perform according to site conditions?
Category: Pumps
Training videos
Where can I fine training animation for pumps and pumping?
Category: Pumps
Eccentric and concentric reducers
Why don’t you use a concentric reducer at pump suction? What is the reason for using an eccentric reducer top flat? Shall it be bottom flat?
Category: Pumps
Replacing wear rings
Can you advise how to replace wear rings on a centrifugal pump? Does it have interference between ring and impeller? How do I go about changing a wear ring?
Category: Pumps
Pump expander installation
I have a question regarding reducers near the pump suction and discharge nozzles for a centrifugal pump for flushing water. The line size is 1 in. and the discharge nozzle size in 3/4 in. The expander is 3/4 in. x 1 in. Should it be near the pump discharge nozzle, i.e. located immediate to the flange, or it can be installed after a length of approximately 1 m? It is my understanding that to reduce the pressure drop in the line, the expander to be located near the pump flange.
Category: Pumps
Recommended material for rotary pumps
What is the recommended material for rotary pumps to manipulate fuel oil 6?
Category: Pumps
Expander installation
Kindly let me know whether the reducer (expander) in a pump discharge nozzle has to be located immediately after the nozzle, or whether it can be located at some distance. The pump is a flushing water pump. The line size is 1.5 in. and the discharge nozzle diameter is 1.25 in.
Category: Pumps
Determine static discharge head
How do you determine static discharge head? Additionally, I have a pump at ground level. Its center line elevation is 0.7 m from the ground. The discharge line goes on the rack at 6 m elevation and travels 100 m. The discharge point elevation from ground is 2 m. Please suggest the correct static discharge head from following cases: Ans 1: 2 - 0.7 = 1.3 m; Ans 2: 6 - 0.7 = 5.3 m. In this case, my final destination is 2 m from the ground, but my discharge line has to travel 6 m up on the pipe rack. Therefore, it is necessary to consider the second option. If my total head (developed head) is greater than 6 m or 5.3 m (i.e. max manometric head of system), then the pump will work and it will not be necessary to consider 5.3 m as static discharge head. Please clarify.
Category: Pumps
Expansion pipe joints
I have some doubts regarding expansion joint applications, before and after pump nozzles, mainly when the fluid being pumped is at normal or low temperature. There are designers that always consider installing expansion joints close to the pump nozzles because of potential piping misalignments, or maybe vibration matters, or something like that. Is that a right practice? On the other hand, IOM manuals of pump suppliers normally don’t state anything regarding flexible joint requirements, except when the temperature is significant. In addition, checking technical brochures issued by expansion joint suppliers, they always recommend installing flexible joints between pumps and piping; but of course, maybe that is a matter of marketing. In fact, other questions are the following: Is it a good practice to always assemble expansion joint between pump and pipes? Which are the right necessities of assembling with expansion joint? Are there any pros and cons about expansion joint installation?
Category: Pumps
Pump reducer location
I have a question regarding reducers near the pump suction and discharge nozzles. I have a centrifugal pump for flushing water. The line size is 1 in. and the discharge nozzle size in 3/4 in. Does the reducer near the pump discharge nozzle need to be located immediate to the flange, or it can be installed after a length of approximately 1 m?
Category: Pumps
Suction piping diameters
Recently one of our clients gave us a copy of their piping standards and said that we are to follow it to the letter unless we can make a case as to why we shouldn't. The problem is that we are installing an HCL purification unit on a very small footprint. The client wants 10 diameters of straight length to the suction of every centrifugal pump. It appears they have copied this standard from a pump manufacturer's design manual. The problem is we do not have the room. The fluids being pumped are cooling tower water, 18%, 22% and 99% HCL. I'm proposing (per your articles and other publications) that I keep the straight length to 5 diameters where space is limited. What is your opinion?
Category: Pumps
Unknown pump performance increase
I have conducted an annual firewater pump test and I am puzzled with the pump curve result that I have obtained. The pump is from the centrifugal pump type and utilizing sea water as the fluid service. I am supposed to compare the pump curve result with the previous year result and I have found out that the pump performance has improved significantly compared to the previous year. This should be good news, but the problem is no improvement work has been done for the pumps for the past two years and theoretically the pump should either maintain its last performance or continue to degrade. I have used a different test procedure from the previous test, in which the main difference is the location of the water discharge. Does the location of the water outlet affect the pump discharge pressure? Will the upstream pressure drop affect the pump discharge pressure? The discharge pressure that I am referring to is the pressure obtained from the pressure gauge located as soon as the pump discharges and not at the end of the pipeline.
Category: Pumps
Vertical centrifugal pump installation
I have a vertical centrifugal pump installation. The eccentric reducer of the suction line is orientated such that the flat side is on the top, which I understand is correct because this reduces the potential for vapor pockets and the possible cavitation problems associated with this. On the discharge line however, the eccentric expander is orientated such that the flat side is on the bottom. The system is being modified to install a slightly larger pump with an increased suction nozzle size and the same discharge nozzle size. The new pump suction nozzle will be the same size and suction piping so the pump will be installed without the suction reducer. Due to the previous offset with the eccentric suction reducer, the elevation of the new pump discharge nozzle will not match the elevation of the discharge piping in its current configuration. If however the eccentric discharge expander is rotated so the flat side is now on the top, the new pump can be made to fit. Can it be a problem to have the flat side of an eccentric discharge expander on the top, or is this in fact the best way for it to be installed?
Category: Pumps
Fluid viscosity and NPSHR
What effect do low viscosity fluids (less than 0.3 cP) have on NPSHR of centrifugal pumps?
Category: Pumps
High pressure sluice water pump problems
I am having some problems with a high pressure sluice water pump in the bottom ash system. It is used to syphon bottom ash from a hopper into a slurry tank. It is an axially split, single-stage, double-suction, 700 hp centrifugal pump. The system is manually operated. During the last part of the ash pull, the amps drop from a normal level of 70 to 50. At that time, the pump experiences high vibration and the outboard bearing (oil lubricated) goes above 200ºF. The operators tell me that at that time, the solids have all been removed from the hopper, and since there is no water level in the tank above, the pump is essentially pulling air. Can this air be causing the pipe to air lock (no flow conditions), essentially deadheading or hammering the pump? If this is the case, the easy solution is to provide the tank with level control to ensure the pump is always pulling either a slurry or straight water. I am not sure if that is the problem.
Category: Pumps
Suction and discharge pump nozzles diameter
Why is the suction line of a pump of larger diameter than the discharge line? Why do we have “reducers” near the pump suction and discharge nozzles?
Category: Pumps
Calculate static discharge head
How do you determine static discharge head? Additionally, I have a pump at ground level. Its center line elevation is 0.7 m from the ground. The discharge line goes on the rack at 6 m elevation and travels 100 m. The discharge point elevation from ground is 2 m. Please suggest the correct static discharge head from following cases:
In this case, my final destination is 2 m from the ground, but my discharge line has to travel 6 m up on the pipe rack. Therefore, it is necessary to consider the second option. In this case, if my total head (developed head) is greater than 6 m or 5.3 m (i.e. max manometric head of system), then the pump will work and it will not be necessary to consider 5.3 m as static discharge head. Please clarify.
Category: Pumps
Determine valve type
I have 5 pumps running parallel (transferring water). Due to pressure fluctuation at discharge (depends on flow requirement of user), I'm planning to install pressure control valve at discharge of the pumps to maintain the pump running at optimum condition. My candidate is a globe valve, but because the line size is quite big (14 in.), the globe valve is not adequate for that application. My engineering consultant suggest to a use butterfly type. According to our experience, using this kind of valve is not effective for pressure control. I need your suggestion as to what kind of valve I have to use when I have a 14-in. discharge.
Category: Pumps
Final destination criteria
What is the criterion used to select final destination of a centrifugal pump discharge line? My pumps discharge line passes through two exchangers and a small mixer. The small mixer outlet enters into another big mixer that is connected to a vapor collection system at the top. Liquid in the big mixer is transported by a pump. Please suggest what my terminal point will be — the small mixer or big mixer?
Category: Pumps
Suction line strainer
How do you determine the type of strainer for the suction line? Which is the best: Y-type, T-type or conical? Does it contribute significant friction loss?
Category: Pumps
Energy efficient pumps
We are running four pumps in our process. The pressure required for the process is 240 psi; each pump flow rate is 27.23 m3/hr; pump head is 180 M; all are multi-stage pumps with a motor capacity of 50 hp. Considering energy conservation, what higher capacity and type of pump can I use?
Category: Pumps
Discharge pressure, flow rate changes
What will be the change in discharge pressure and flow rate of a centrifugal pump when pressure at the suction side increases by a certain amount due to change in process conditions? Answers correlating the problem with H-Q curve and system curve will be more convincing for me.
Category: Pumps
Pressure-boosting pump
Please advise a pump type (types) for the following pressure boosting application:
- relatively low viscosity fluid, 403 micro Pa-s,
- specific gravity, 1.34,
- flow rate, 0.161 l/s (2.6 USGPM),
- DeltaP, 676 kPa (98 psi),
- Temperature, 22C
- NPSHA about 3 meters.
We are considering a regenerative turbine type pump, but are looking for alternatives. What would be the best choice if low bhp was the primary performance criteria?
Category: Pumps
Pump shaft failures
We have three double suction pumps operating in parallel. These pumps are high suction specific speed pumps handling cooling water, having a differential head of 43 m and a flow rate per pump of 7,000 h3/hr. The pumps are motor driven and run at a speed of 753 rpm at 50Hz. The pumps have two radial journal bearings and one thrust bearing at the non-drive end. Shortly after commissioning, there are shaft failures at the location near suction eye towards the motor. No other damages/indications are evident. Can you give me the probable reasons for the failure of shafts? How do I calculate the radial load acting on the shaft? We have tried to solve the problem by increasing the shaft material strength, but in vain.
The failure is happening on all the three pumps. The interval between failures varies from 11 days to 2 months. The failure is brittle in nature. The breakage is not at the change in diameter. In fact, the failure is at location of maximum diameter, where the impeller is mounted on the shaft. No seal or bearing failure has been noticed in all of these failures.
Category: Pumps
Pump suction lift
I read that the suction lift of any pump is a maximum of 34 feet ideally, but actual it's round about 22 feet for positive displacement pump and 15 for dynamic pumps. How can we get water in the house where the depth of water is more than 200 feet? Which type of pump is used there? Also, what is meant by donkey pump? How suction is carry out in the pump's suction side?
Category: Pumps
Alternative pump solutions
We have received a special proposal and type of pump from a particular vendor for the following conditions. This type of pump is very heavy and we prefer to use simple, horizontal pumps instead. Please advise alternative solutions, if possible.
Category: Pumps
Quantifying liquid density effects on NPSH
When calculating NPSH available for specific pump in diesel service, I have found some contradictory data in the literature concerning the fluid density influence on NPSH required for the pump. For example, if NPSH required for the pump is equal to 3m of water at 20°C (liquid density = 1kg/dm3), what is the NPSH required for subcooled diesel liquid at 200°C, with liquid mass density of 0.635kg/dm3 at process conditions, for the same pump (diesel vapor pressure is insignificant)? Is it equal to 3m, is it lower because of lower liquid density compared to water, or is it higher because of lower hydrostatic pressure at pump suction? I have NPSH available of 4.8m of subcooled diesel at pump suction centerline, and I wonder how can I recalculate it on water terms, in order I could compare my NPSHav with NPSHr which is given for subcooled water. Generally, what is the way of comparing NPSHav (process fluid) with NPSHr given for water at 20°C? There must be some formula to quantify liquid density effects on NPSH required.
Category: Pumps
Configuration for centrifical water sludge pumps
We are using centrifical water sludge pumps with 1 1/2 inch and 2 inch discharge outlets with direct drive connect to 110 or 220 volt 1/2 and 2 hp electric motor. We are pumpimg 1000 litre batches of 50% by weight verticle less than 10 feet. A 50% by weight mixture of non disolved fine grandular chemical with specific gravity of 1.68 and water. The 1/2 hp motor regularily blows 15 amp fuse on 110 ten.The 2 hp motor always blows 30 amp fuse on 220 volt. What configuration would work?
Category: Pumps
What is the limitation to specify the minimum flow of the centrifugal pumps?
What is the limitation to specify the minimum flow of the centrifugal pumps? is it vibration increase or temprature increase or etc?
Category: Pumps
Correct arrangement for isolation and NRV valves
In chemical plants and refinery service normally two pumps are installed, one running and the other stand-by. In the discharge of each centrifugal pump an isolation valve and non-return are provided. Sometimes the isolation valve is installed before the NRV, and sometimes the other way. Please indicate the correct arrangement considering maintenance safety. Please also indicate whether the NRV is to be installed in horizontal or vertical part of the piping.
Category: Pumps
Best selection criteria for a centrifugal pump
We need to select a centrifugal pump with a flow control valve in the discharge line, connected in the other line, which is an another centrifugal pump discharge with a level control valve. What is the best selection criteria (performance curve) for a centrifugal pump where head (and flow both) may vary yet, the pump should not see a 'closed discharge'?
Category: Pumps
Drop curves for a single convolution expansion joint
I'm looking for pressure drop curves for a 12" single convolution expansion joint. I've checked several manufacturers websites, but none publish pressure drop curves. Any hints?
Category: Pumps
