variable speed centrifugal and reciprocating pump
variable speed centrifugal and reciprocating pump
(OP)
Does a variable speed centrifugal pump make sense as a booster for a reciprocating pump? I believe some of my colleagues are proposing such a system. Perhaps they think that a control valve and return line are unnecessary, or they believe the centrifugal pump can be made to operate close to its BEP.
I'm thinking that once the flow rate of a reciprocating pump is set (by its speed), that's it. One cannot send any more fluid than the pump will take and if one sends less, the reciprocating pump will cavitate. Looks like some kind of return line is needed.
Also, since the flow rate to reciprocating pump should remain constant, is it fair to say that the discharge head has a largely static component? I understand that variable speed drives are not worth using if the load consists of static head.
Thoughts/insights are welcome.
I'm thinking that once the flow rate of a reciprocating pump is set (by its speed), that's it. One cannot send any more fluid than the pump will take and if one sends less, the reciprocating pump will cavitate. Looks like some kind of return line is needed.
Also, since the flow rate to reciprocating pump should remain constant, is it fair to say that the discharge head has a largely static component? I understand that variable speed drives are not worth using if the load consists of static head.
Thoughts/insights are welcome.





RE: variable speed centrifugal and reciprocating pump
There were 4 pumps each delivering 500+ litres per minute at 350 BAR.
The slippers and the piston were not tied together so the pump could not pull oil in.
The centrifugal pump ran all the time at a fixed speed. The piston pumps were also fixed speed.
Thinking about it...why would you have a variable speed centrifugal pump with a fixed speed reciprocating pump?
The demand of the reciprocating pump is known. If you overspeed the centrifugal pump the flow will drop, then the reciprocating pump will cavitate.
As I understand it, it is better to have a fixed displacement pump and run it against a closed head. When the reciprocating pump starts up, the pressure in the centrifugal pump will drop off and pump will run along its efficiency curve.
I would imagine the max flow rate of the centrifugal pump should be about 10-15% above that of the reciprocating pump just to allow for any drops in performance.
Hydromech
RE: variable speed centrifugal and reciprocating pump
The idea is to boost inlet pressure to the recip. If you need to do that at all recip speeds covering a wide range of flows, a centrifugal upstream could certainly supply a boosting pressure over its operating flow range.
The centrifugal could do that using either a fixed speed or variable speed drive.
If using a fixed centrifugal speed drive you will deliver flow to the recip according to the one curve the centrifugal has at that speed. If the pressure is too high for the recip suction for some reason, (adding that to the recip's suction pressure would exceed the inlet pressure rating or casing pressure or discharge pressure of the recip) you will have to control it. If you control it, you will be forced to waste some energy.
If you use a variable speed drive for the centrifugal, you will be able to adjust the centrifugal's curve hopefully to make a closer match to the recip's suction requirements. If designed correctly, you will probably be able to keep pressures and flows within the recip's requirements and NOT need a control valve and thus you will not waste the energy that the control valve would consume. That is the cost benefit that counters the cost of the variable speed drive. Compare those for the life of the equipment and see if it makes economic sense too.
BTW ..never run a recip against a closed valve without a full flow safety relief between them.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: variable speed centrifugal and reciprocating pump
Things go bang if you run a fixed, positive displacement pump against a closed head without a relief valve installed.
Hydromech
RE: variable speed centrifugal and reciprocating pump
A reciprocating pump will cause pressure and flow fluctuations in both suction and discharge lines. If you are controlling the centrifugal VSD with pressure or flow, the VSD will have problems chasing the signal.
RE: variable speed centrifugal and reciprocating pump
RE: variable speed centrifugal and reciprocating pump
RE: variable speed centrifugal and reciprocating pump
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com