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Total developed head (TDH) and differential head
Total developed head (TDH) and differential head
Total developed head (TDH) and differential head are the same. If a pump curve indicated 30' TDH at zero flow, then the discharge (downstream) pressure is not atmospheric; it is at its maximum value (shutoff). The pressure would be =
Suction pressure + TDH/2.31*sp_gr
where TDH = head in feet and sp_gr = fluid's specific gravity at flowing conditions.
Frankly, you are asking enough questions about this suject to make me nervous. The asking of questions is good, but if you are sizing safety valves then I think you are not sufficiently knowledgable about your systems to be able to do so without help. Please get a person experienced in sizing PSV's to help you.
Thank you SeanB & djack. I just have one follow-up question, though. As SeanB mentioned, the required relief rate should be the rated flow of the pump (at the relief valve's set press. plus overpressure). My question then is can this flow from the pump curve be increased to account for any static suction head that may be present upon discharge from the relief valve or is the flow from the pump curve the max flow possible (ignoring any friction losses and/or static discharge head present for the time being). For example, say at the absolute allowable relieving pressure of 114.7 psia for the RV, the pump curve gives a value of 100 gpm. There is also 50' of static suction head. Would it be incorrect to account for this and move to the right on the curve and increase the required relief rate? Thanks for the help. In-line pumps
2011-07-11
