NPSH and temperature
NPSH and temperature
(OP)
Can a self-priming pump in a sump application (ie 6ft of suction lift and 20ft of discharge head) handle hot water? I know that as pressure decreases, boiling point of water drops as well. What do I need to know to figure out at what temperature my pump will boil the water it is lifting (and lose its prime)?





RE: NPSH and temperature
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: NPSH and temperature
My concern is that as temp goes up and vapor pressure increases, available NPSH may be less than required NPSH
RE: NPSH and temperature
Head of water atmospheric pressure is about 33ft. Subtract the vapour pressure at 180 about 16ft. Subtract your lift (pump cl minus water level) 6 ft.Subtract inlet pipe losses say 2 ft What's left is NPSHA - about 8 ft. Bit low and pump might be cavitating.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: NPSH and temperature
a) Get the pump vendor to run a witnessed NPSH test at the operating temp range.
b) Use the graph in fig 10-25 in Perry Chem Engg Handbook - 7th edition, which is abstracted from the Hydraulics Inst Standard.
RE: NPSH and temperature
RE: NPSH and temperature
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: NPSH and temperature
Well, that seems a bit strange. While it's unlikely they will give you an exact figure for the pressure at the eye of the impeller, they do tell you NPSHr by the pump, right?
If you can't follow LittleInch's post and draw conclusions from that, you have no business selling a pump to anyone.
RE: NPSH and temperature
I was able to convert everything into absolute pressure and figure out what my static inlet pressure would be, then cross reference vapor pressure of water chart to find my boiling point at that temp. Seems im ok and will not boil water on my suction side until about 198°F. Still not sure if that will change when the pump is running (especially when starting a cycle).
@tenpenny keep your opinions to yourself. If you don't have anything productive to add to a discussion, don't post. The whole purpose of a forum is to share information and ask questions. I want to know if my installation will work before bidding a job. So I ask to educate myself. Nothing wrong with that.
RE: NPSH and temperature
The boiling point issue is a red herring. The pump will start to cavitiate badly at a temperature / vapour pressure below the actual boiling point.
The NPSHR figure from the pump vendor is your first point of call. You need to have enough NPSH to be at or above that number. A key part of the calculation for you is the vapour pressure of the water at your pumping temperature (180F)
However that isn't the end of the story. NPSH is based on a head loss of 3% from normal operation. Cavitation can often start at a level higher than NPSH, so the normal rule is to allow at least 1m (3ft) above the NPSHR to allow for this.
Please advise what the pump NPSHR figure is.
I think your system is right on the limit and possibly below for many pumps.
Please don't respond to posts you don't like in that fashion. It's frowned on in these forums and your post might end up being red flagged and deleted.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.