NPSH Safety Factor

[CrazyHorse81]

My first post :woot: -

I work mainly in potable water booster stations, sewage lift station, and sludge pumps. When I read a NPSHr curve, what safety factor do you use when computing NPSHa? I use a NPSHa/NPSHr ratio of 1.10 to 1.15, but have read that some use 1.50. A fellow worker says to use 5' for all applications. I don't like that approach. What are your thoughts? Any good references for application? In the CERM they only mention that it is desireable in practice...so they don't have a straight answer as with the rest of my reference books...

Regards,

 

[Chucktown PE]

I look at each situation differently. If there is a lot of suction piping and a large suction lift I typically add a little bit of a safety factor into my friction losses (use C = 100 instead of C = 120) in the piping. But if NPSHa > NPSHr you shouldn't have any problems. I have only had one project where we were even close and I didn't use a safety factor other than what I described above. That pump station is working fine.