Recip PD Pump Piping Question
Recip PD Pump Piping Question
(OP)
Gentlemen,
For Recip. PD pump piping design, a well known best practice is to install a bypass or recirculation line from the pump discharge back to the pump suction/inlet. This aids in pump start-up where a high amount of mechanical inertia requires high starting torques & power from the motor.
One resource I've read states that this bypass/recirculation line should "take liquid back to the liquid source and not into inlet line."
I've seen it done both ways. Does anyone know the technical basis behind this specific requirement? The only advantage I can see to route the bypass line back to a tank would be to eliminate any air or gas in the pump or inlet line at start-up. I'll also note that these pump motors will be driven by VFDs, which will also aid in easing the start-ups.
Thanks
For Recip. PD pump piping design, a well known best practice is to install a bypass or recirculation line from the pump discharge back to the pump suction/inlet. This aids in pump start-up where a high amount of mechanical inertia requires high starting torques & power from the motor.
One resource I've read states that this bypass/recirculation line should "take liquid back to the liquid source and not into inlet line."
I've seen it done both ways. Does anyone know the technical basis behind this specific requirement? The only advantage I can see to route the bypass line back to a tank would be to eliminate any air or gas in the pump or inlet line at start-up. I'll also note that these pump motors will be driven by VFDs, which will also aid in easing the start-ups.
Thanks





RE: Recip PD Pump Piping Question
Johnny Pellin
RE: Recip PD Pump Piping Question
RE: Recip PD Pump Piping Question
The main issue as JJ says is heat accumulation.
Some pumps include this internally within the pump, but most people prefer to have their own system which is specific to your requirement and can be repaired and maintained much easier.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Recip PD Pump Piping Question
My only problem now is my meters upstream of these pumps will be measuring the same volumes twice during this bypass operation (start-up). Time to get the PLC programmer geeks involved ...
RE: Recip PD Pump Piping Question
RE: Recip PD Pump Piping Question
The devil is in the detail. If your relief disposal system is a multi-user system and quite small or long, you could raise the pressure in it to affect operation of some other relief systems.
Metering upstream is now not a good place to meter anything that occurs d/s of the pump. metering, especially fiscal metering, needs to be as close to the end point as you can and not have multiple paths.
Only if you have 100% of flow either in the bypass or the main line will a software switch be able to stop / start flow metering. Seems like a poor location to me for the meters.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Recip PD Pump Piping Question
RE: Recip PD Pump Piping Question
Re: metering with PD pumps - meter types are bidirectional coriolis meters. The suction & discharge stabilizers on each pump will also smooth out the pulsed flow. Not to mention there are also check valves between u/s meters & d/s pumps.
Little Inch - Code explicitly allows for designing for only one upset condition at a time in any shared relief system. Anything beyond that would be considered double jeopardy. Also, the leak detection/allocation meters u/s of pumps should never be measuring multi-path (split) flow. Prior to bypass mode start, the outgoing station valves will be closed. As an origination station, we are required to have leak detection/allocation meters tracking the outgoing volumes.