Linear pump/reciprocating pump
Linear pump/reciprocating pump
(OP)
Hi All,
I am designing a test rig for a reciprocating pump and motor assembly to obtain the system curves etc...
The problem is how am i going to increase the inlet pressure for this pump (manufacturer suggested an inlet pressure around 10psi-100psi)?
If i add a pump at the inlet say a centrifugal pump to reach the required head, what effect would that have on the performance of the reciprocating pump?
Any suggestions would be greatly appreciated!!
Regards
I am designing a test rig for a reciprocating pump and motor assembly to obtain the system curves etc...
The problem is how am i going to increase the inlet pressure for this pump (manufacturer suggested an inlet pressure around 10psi-100psi)?
If i add a pump at the inlet say a centrifugal pump to reach the required head, what effect would that have on the performance of the reciprocating pump?
Any suggestions would be greatly appreciated!!
Regards





RE: Linear pump/reciprocating pump
The pump supplier said that 1 centrifugal pump, even with a 100 HP could not accomplish it because it was so far to the left on the performance curve. So what they setup was a smaller, high pressure pump to feed into the big pump. The small pump got something like 50-100 psi at 40 GPM. Then the big pump stepped it up to the 400-600 psi as we needed.
They just added the pressures.
RE: Linear pump/reciprocating pump
To use a centrifugal pump as a booster pump is common and will not have any negative effect to the performance of the reciprocating pump. But the centrifugal pump must provide higher flow than the reciprocating pump. How much depends upon your answers to above mentioned questions.
RE: Linear pump/reciprocating pump
1) Flowrate: Size the flowrate of the centrifugal charge pumps for 150% of the reciprocating pump's flowrate. For example if the reciprocating pump's flowrate is 200 GPM then the CP pump should be sized for 300 GPM.
2) Impellor Size & Motor Speed: Charge pumps are not a constant flow application. The discharge flowrate of the charge pump must accelerate and decelerate to match the variation in flow of the reciprocating pump that it feeds. Small impellors operating at 1750 RPM tend to slip through the fluid when acceleration is needed. (Similar to car tires slipping on wet pavement.) Although the pump curves may show that enough head will be available at 1750 RPM with a small impellor shock loading may occur. To avoid this charge pumps should have larger impellors running at either 1150 RPM or 1450 RPM. For example a 6 x 5 x 14 with a 13.5" impellor (14" max. on this model) would work well, where a 10 or an 11" impellor would not be recommended.
3) Head: Make sure that you take any loses in the suction piping or losses for high vapor pressure into consideration, and be sure that charge pumps is sized to produce a minimum of 150% of the NPSHr.
4) Location of Charge Pump:
A charge pump should be placed as close to the supply tank or source as possible. For this reason many charge pumps are a long ways away from the location of the reciprocating pump so they can be closer to the tank.
5) Drive for on Charge Pump: If you place the charge pump next to the reciprocating pump you can belt drive a speed increaser to the non-drive side of a double extended crankshaft. If you don't have a double extended crankshaft, you can direct couple an electric motor to the charge pumps. If electricity is not available, you can belt drive the charge pump from the PTO of the Gas or Diesel Engine that drives the reciprocating pump. Be sure to add the charge pump BHP to the HP requirement when sizing the main drive if you are belt driving it to the PTO or the opposite end of the pump crankshaft.
RE: Linear pump/reciprocating pump
The purpose of the charge pump to a reciprocating pump is simple to ensure that the pump has adequate suction to avoid cavitation. Request and NPSHr curve from the manufacture to establish how much head is required at the suction of the pump. Since Reciprocating pumps don't produce head, the pressure at the suction does not change the flowrate or discharge pressure of the reciprocating pump.
RE: Linear pump/reciprocating pump
thank you for your response!
The NPSHr is not specified by the manufacturer because it is a bespoke design for a particular application. Hence the supplier did not perform any tests on similar pumps before and the supplier is relying on us to test the pump. The pump only has 2check valves for openening and closing and a piston in rod config...
I am not sure if i understood the concept properly regarding the flow rate of the charge pump... to my understanding if i choose the flow rate too high the motor has to overcome the force generated by the inrush flow rate hence the power requirements on the motor would increase!!
I was advised not to use a centrifugal pump because this may have an adverse effect on the check valves...
i feel more confused than ever before... can anyone point me in the right direction please.... maybe i am not understanding the performance of the pump correctly..
Thank you all for the support..
RE: Linear pump/reciprocating pump
I'm not sure why you need a charge pump at all if you have a single acting piston or plunger pump. These pumps usually have an excellent suction capability and do not necessarily require a positive inlet pressure (= positive gauge pressure). Do you tell us the pump brand and perhaps model? I think that is important to understand the problem.
RE: Linear pump/reciprocating pump
RE: Linear pump/reciprocating pump
Just double checked the pump, the pump has a long plunger in a rod and has two check valves.
The manufacturer said we need pressure at the inlet and the outlet is set to 4kpsi. i cannot raise the feed tank higher than 2 m above ground level because i simply dont have space in workshop...
the pump is running at high speeds and it is a learning curve for manufactuerer as well.
i was thinking in the lines of curtis26 a pump at the inlet should do the trick but other engineers reckon that the pump performance is compromised due to flow rate generated by centrigal pump...
Thanks all for replying..
RE: Linear pump/reciprocating pump
RE: Linear pump/reciprocating pump
The CP's will not generate flowrate. It will produce a constant head at the suction side of the pump. A piston pump is a positive displacement devise, so as long as its NPSHr is met it is going to have the same discharge flowrate at 10 PSI suction as it does at 100 PSI suction (and the same if its NPSHr is achieved with a boosted pump, elevated tank, etc).
If it makes any difference, I have been to a few multiplex pump manufactures' test facilities, and all of them had CP charge pumps to feed their test stand for performance testing.
RE: Linear pump/reciprocating pump
10-100PSI suction pressure is a very wide range. Pump manufacturer should be able to estimate more closely the NPSP for the pump.
You can install a pulsation dampener / accumulator as close as possible to the recip pump suction so that you do not need to oversize the charge pump flow rate and also less pulsation in the suction flow.
RE: Linear pump/reciprocating pump
RE: Linear pump/reciprocating pump
If you insist on CP, then make sure the curve is as flat as possible to avoid as much head change over flow range. Centrifugal with a steep curve will apply head pressures that vary with flow. A performance curve that is essentially flat throughout the flow range will deliver essentially contant head.
Of course the CP will have some sort of NPSH requirements as well.