Booster Pump to PD Pump
Booster Pump to PD Pump
(OP)
I just wanted to double check something. If I have a booster pump (centrifigul) upstream of my pd pump, and the booster pump has a lower discharge flow rate compared to the discharge rate of my pd pump it will create cavitation and vibrations. Is it true that the bigger the difference the stronger the vibrations?





RE: Booster Pump to PD Pump
RE: Booster Pump to PD Pump
Th PD will demand flow from the centrifugal. The effect on an undersized centrifugal will be that it will be forced rightwards along its head-capacity curve in an effort to provide the flow demanded by the PD. This will occur at lower differential head (hence delivery pressure) from the centrifugal to the PD. if the equilibrium point is far to the right along the centrifugal's head-capacity curve, the suction pressure to the PD can be reduced to the point where cavitation will occur. Indeed, cavitation might also occur in the centrifugal, but possibly of more concern will be its sustained operation at run-out conditions that, in addition to vibration, might overload the motor.
RE: Booster Pump to PD Pump
Just a heads up, I'm kinda new to the industry so my next question might seem a bit dumb.
micalbrah: The pd pump is a piston pump. It's being in use right now and there's lots of problems in the building.
Snorgy:If my centrifigul pump is set at a certain flow rate, how will it know it needs to increase the flowrate?
RE: Booster Pump to PD Pump
The easiest condition check you can do is install a compound vacuum/pressure gage between the discharge of the centrifugal pump and the suction of the piston pump. If the pressure stays above the NPSHR of the piston pump at all times, you don't have a problem.
If the inter-pump pressure goes below the NPSHR of the piston pump, then you need a bigger or faster or rebuilt supercharge pump, or you need to clear the clog from its inlet.
Also note that centrifugal pump curves are typically provided for water. If you're pumping something else, you need to correct the curves or the math. Check the detailed data sheets for the centrifugal pump, and look up 'affinity laws'.
Mike Halloran
Pembroke Pines, FL, USA
RE: Booster Pump to PD Pump
RE: Booster Pump to PD Pump
With respect to your question, the centrifugal pump will only operate at a given instant in time on one point along its characteristic head-capacity curve, and that point will be where the system head curve intersects the pump characteristic. Thus, when the PD pump begins to demand more flow than can be delivered by the centrifugal pump corresponding to that point, the intermediate pressure falls and the centrifugal pump will automatically deliver more flow at lower head - in other words, the operating point shifts to the right to a new intersection point. The reverse is true when the PD pump demands less flow - the centrifugal pump operating point shifts to the left to an intersection corresponding to less flow at higher head. It's actually the hydraulic resistance in the piping system between the pumps that sets the flow from the booster.
Hence my question about flow control. Be careful how this is set up.
RE: Booster Pump to PD Pump
RE: Booster Pump to PD Pump
RE: Booster Pump to PD Pump
Again, *my experience has been* that plunger pumps like to see about 25 psig at their suction flange; otherwise, vapor pressure, line losses and acceleration head *I have observed* contribute to the onset of cavitation due to the separation of the plunger face from the incoming fluid on the plunger's receeding stroke. You also need to make sure the pulsation dampeners are set up and tuned correctly.
Your experience might be better than mine. I am only relating what I have seen.
It does cause damage over time, such as was the case several years ago when I was called to the field to look at a triplex in water service that had blown apart, shattered all three plungers and expelled the crank from the casing.