I am sizing a relief device for a situation in which a centrifugal pump could overpressure a vessel. Generally speaking, I have seen cent. pump curves that denote the y-axis as Total Developed Head (TDH) and others as differential head. Are these really implying two different values? If a pump curve reads a TDH of 30' at zero flow, does this assume that there is no pressure downstream? Also, when determining the required relief rate for a PSV using the cent. pump curve, how is the flow adjusted to account for static suction head? Is the amount of static suction head (in feet) simply added to the pump curve?
Any resources or articles on sizing PSVs for centrifugal pumps would be greatly apprectiated. I have read many manuf. sites, but none seem to go into detail about these types of situations; where you are dealing not only with a shut off pressure, but also with different suction and discharge heads and how they may affect the pump curve. Thank you for your time.You have to calculate the maximum discharge pressure from your pump. Generally, you calculate it 2 ways:
1. Normal Discharge Pressure + Maximum Suction Pressure OR
2. Normal Suction Pressure + Pump Shutoff Pressure.
You should calculate both and the greater of the two will be the maximum developed pressure from the pump. The required relief rate should be the rated flow of the pump.
I hope this helps.Vacuum pumps

2011-07-11

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