Operating of reciprocating pump

[sujins]

Please any expert explain when operating reciprocating pump. If the process require flow rate with lower pressure than discharge pressure from pump. Let's say required pressure = 5 barg but discharge from pump is 414 barg. How can we reduce pressure? Is it adjustable to achieve the desired value from reciprocating pump?

 

[Montemayor]

sujins:

I don't know the extent of your pump experience, but one basic fact about all pumps is: the pump doesn't set discharge pressure - the process does. The pump conforms its discharge pressure to suit the existing process pressure. This is true for all pumps.

If you are using a PD pump you have a wide range of available discharge pressures the pump can pump to. If you happen to be using a centrifugal type pump (which is not your case), then you are limited in achieving a discharge pressure by the characteristics of the performance curve and its dead head pressure.

Your reciprocating PD pump will have no problem in pumping liquid into your 5 barg system. Its discharge pressure will be the 5 barg you seek plus the pressure drop required to get it to the point you need it at.

 

[sujins]

My question is that if I need the pump to run at discharge pressure of 5 barg to compensate for the pressure drop in the discharge line and achieve the required process pressure at around 0.5 barg, then can I adjust the discharge pressure at the pump or it will automatically supply the pressure to suit the existing process pressure as you mentioned. Or I have to set the pressure at the pump(Because the performance curve is different from centrifugal type).If yes how to do that. If not,do I need to have a pressure control system to regulate the discharge pressure from 414 barg to 5 barg.

I have a little experience about reciprocating pump. Could you give suggestion?
Thanks.

 

[25362]

As I see it, PD reciprocating pumps, operating at constant speed, deliver approximately an average constant liquid volume flow rate independent of pressure levels, although with flow pulsations resulting from individual fluid displacements. The liquid is assumed incompressible.

The discharge pressure (within design limits) is determined by the system resistance and back pressure as Montemayor explained.

Thus I assume you'd have to look for flow control rather than pressure control.

 

[svanels]

Hm...
5 bar back pressure, and the pump is set/capable at 414 bar??

It needs one idiot to close a valve, to shoot the equipment to the moon..

How could you reduce the pressure? Just reduce the speed of the pump.

 

[Ashereng]

Let's say required pressure = 5 barg but discharge from pump is 414 barg. How can we reduce pressure?

Am I missing something or is 5 bar to 414 bar is a huge difference, no?

This is a bit simplistic, but, a different pump?

 

[CanuckMiner]

As others have stated, I don't think you have a problem with your pump, other than the fact that it appears to be vastly oversized for your duty. However, you should protect the pipe system by installing a pressure relief valve upstream of any isolation valves on the system. Have the relief valve set to something higher than the 5 bar, but not too low (to avoid nuisance trips). This should prevent the equipment going into orbit.

Reducing the speed of a reciprocating pump will not reduce the pressure; it will only reduce the flow.

Cheers,
CanuckMiner

 

[svanels]

The flow causes the pressure, hence reducing the flow, reduces the pressure. That is if you have over-capacity.
But the application give the impression of gross over-dimensioning. Something like a Volkswagen with a jet engine...

 

[25362]

I wonder whether -in principle- the discharge valves of the high-pressure pump need higher discharge pressures to be properly activated.

 

[quark]

Not necessarily, IMHO, because it is the pressure difference across the valve that comes into picture and this is a positive displacement application. I even don't advise controlling the discharge of a reciprocating pump by complementing it with a safety valve. The pressure builds up and safety valve opens most of the times. This is a common phenomenon in aerobic lagoons of effluent treatment plants (ofcourse with blowers).

 

[mk3223]

Here are some points to look at:
1. It may waste energy to run a 414barg PD pump for the 5barg process. I assume it was a small flow application.
2. If your PD pump have a speed controller, you could adjust the speed to reduce the pump discharge head.
3. Based on the required flow you needed, you may adjust the pump stroke length to set new discharge flow.
4. You don't want to overpressure the new system. If cost effective, you could install a pressure reducing valve on the discharge to reduce the pressure.
5. Also, you may want to reset or replace the PSV valve on the PD pump discharge (for system protection).
6. You may review the pump manual for the PD pump you have to see how much you could do to this pump. if any double, you should check the pump dealer for more info.

Remember, the safety first and good luck.

 

[DiaphragmPumps]

Some confusing answers, I hope I can clarify. If you have a piston pump for example, the pressure capability will be based on the build of the unit and the size of the motor driving it. so it is perfectly acceptable to run this pump at 5 bar,should however the pipe block, you have a lot of potential pressure to remove the blockage or damage something. Hence the need for PRV's. If you only need 5 bar then a PRV for 400 bar is unecessary, you might as well fit a 10 bar unit and save all the problems with High pressure PRV's. Alternatively have you considered an Air Operated Diaphragm Pump

http://www.diaphragmpumps.co.uk

you can set your air pressure to 5.5 bar and forget it. because if the pipe blocks the pump will stall at 5.5 bar without damage to the pump or system.

 

[tundelash]

Pressure
^ .
| .
| .
| . System Curve
|______________._____________________
| .
| .
| .
| .
| .
_|__.______________________________
| ---> Flow
|

The graph above shows the pressure-flow relationship for reciprocating pumps. As you can see, you can only change the flow by changing reducing or increasing the speed. The system curve is dependent on your operation, and the pressure P-414 is dependent on the pump design (your swept volume, the piston diameter etc).

The implication is that you cannot change the pressure profile unless you change the pump configuration/design itself. Changing settings on the pump may not be feasible as usually done with reciprocating compressors. Installing a flow control valve on the discharge only helps to control flow. A pressure control valve or relief dissipates the pressure to accpetable points, but can't see the practicality of this with a turndown of 414bar to 5 bars, so would only suggest a pump replacement to the acceptable point (for this kind of turndown).

 

[quark]

tundelash,

Positive displacement pumps give you constant flowrate any head and that is why the performance curve of a PD pump is a straight line parallel to ordinate (not abscissa).