NPSHR for Condensate Application

NPSHr is a function of the pump design, specifically the design of the impeller and its suction eye. There is no "AVERAGE NPSHR VALUE ".

TGIF

u r correct saying that there is no such thing "average NPSHR"

But I have an application where NPSHA is very less (less than 2m). For this I want to know whether this will be sufficient to cater the NPSHR or I have to change the equipment layout (which costs). But if I would know the NPSHR for this flow and head pump I can take a decision on it.

Read tornado's note. Only the pump manufacturer can answer your question as it is specific to the pump installed. There is no generic answer.

You appear to have a very low flow high head application. What kind of pump are you using?

as per client specifications we are using API 674 pumps, because API 676 will not give such high head at low flows, but we have low NPSH available.

in previous ONGC projects we came across data sheet of HASKEL pumps (gas driven plunger) wherein NPSHR mentioned is "negative 1 meter". Negative means pumps is capable of handling gases with liquid. Please correct my understanding.

Tornado was very polite in calling this "unconventional".

NPSHa should always exceed NPSHr. API 674 tells you to consider lower speeds if NPSHr is within 1,5 m of NPSHa (including system acceleration head).

Remember that you are looking not only at the NPSH (NPIP is also used sometimes with PD pumps, but it means the same thing) as you would for a centrifugal pump, but also at the system acceleration head. You need to take this into account as well when calculating the available NPSH. Read Appendix G of API 674 for a good explanation. To calculate acceleration head:

There should be a manufacturer's specification sheet or catalog data that gives the NPSHR for the pump being used; sometimes this is shown on the pump curve. The NPSHR tends to rise considerably at very low and very high flows, so hopefully your pump has been selected so it will run near the middle of its curve. Cornell Pump (Portland, OR, USA) has good literature on this topic. (They make refrigerant pumps, which operate at near-saturated fluid conditions, hence NPSHR (versus A) must be checked carefully in each application.) Condensate conditions will be similar.

This looks as if it may be an unconventional use of the term "NPSHR". If possible, you should contact a Haskel representative for clarification. Describe your conditions and geometry, and they should be able to tell you if your sytem will meet the NPSHR.

(A similar thing happens when water pumps are described as capable of such-and-such "suction lift." When you correctly include atmospheric pressure, you find that the NPSHA is actually positive.)