PUMP NPSHA
PUMP NPSHA
(OP)
A PUMP HAS ITS NPSHA DEFINED. IT IS DECIDED TO USE THE SAME PUMP WITH A DIFFERENT LIQUID.
THE TWO FACTORS THAT WOULD AFFECT THE NPSHA WOULD BE THE NEW VAPOR PRESSURE AND THE NEW SP GR.
IS THERE A RULE OF THUMB TO EVALUATE THE NPSHA WITHOUT HAVING TO DO MORE DETAILED CALCULATIONS?
THANK YOU VERY MUCH
WOULD YOU ALSO KNOW HOW ONE CAN SEND A MESSAGE OR QUESTION DIRECTLY TO A MVP, THIS SITE SEEMS TO BE SO CLOSE-FISTED THAT I HAVE NOT BEEN ABLE TO FIND OUT
WOULD SOMEONE AUTHORITATIVE RESPOND BY THIS AFTERNOON?
THE TWO FACTORS THAT WOULD AFFECT THE NPSHA WOULD BE THE NEW VAPOR PRESSURE AND THE NEW SP GR.
IS THERE A RULE OF THUMB TO EVALUATE THE NPSHA WITHOUT HAVING TO DO MORE DETAILED CALCULATIONS?
THANK YOU VERY MUCH
WOULD YOU ALSO KNOW HOW ONE CAN SEND A MESSAGE OR QUESTION DIRECTLY TO A MVP, THIS SITE SEEMS TO BE SO CLOSE-FISTED THAT I HAVE NOT BEEN ABLE TO FIND OUT
WOULD SOMEONE AUTHORITATIVE RESPOND BY THIS AFTERNOON?





RE: PUMP NPSHA
The pump has it's NPSHR defined. The NPSHA is calculated for the specific liquid and as well as vapour pressure, specific gravity it is also affected by the pressure losses in the incoming system which are affected by the viscosity of the fluid. So no, there is no really simple way to determine the NPSHA of a fluid which has changed from the one originally calculated.
There is no way I know of to directly contact an MVP outside of the forum and that's the way most MVPs like it as it avoids spam and lots of direct (free) advice being sought.
Is this a real question or theory / student work? If you give some numbers and details you might get a better answer....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: PUMP NPSHA
A person should be able to verify the process conditions and determine the NPSH in 2-3 hours.
RE: PUMP NPSHA
This is a cryogenic in-pot centrifugal pump designed for ethylene service, but tested on propane
Ethylene VP 282 psia SG 0.44 Viscosity 0.074 cp Npsha 9.7 ft to inducer c'l Pumping temp -23 F Flow 2160 gpm Npshr 5.2 ft to same datum
Propane VP higher than that of ethylene Npsha less than 9.7 ft because of higher vapor pressure of propane Testing temp = - 47 C = - 53 F Flow 2160 gpm
Required: To calculate Npsha for propane to same datum. Point is to calculate this from the 9.7 ft for ethylene, with somewhat minimal calculations, rather than from scratch
thank you
RE: PUMP NPSHA
WOULD YOU ALSO KNOW HOW ONE CAN SEND A MESSAGE OR QUESTION DIRECTLY TO A MVP, THIS SITE SEEMS TO BE SO CLOSE-FISTED THAT I HAVE NOT BEEN ABLE TO FIND OUT
WOULD SOMEONE AUTHORITATIVE RESPOND BY THIS AFTERNOON?
Of course a polite request would never go amiss instead of demanding answers.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: PUMP NPSHA
So, assuming with ethylene you need 5.2 ft of NPSHR at 2160 gpm, you need 5.2 ft when pumping 2160 gpm of propane.
Since it's likely that the ethylene and propane are both saturated liquids, then the NPSHA is the vertical head of liquid from the centerline of the pump to the liquid level minus the suction piping line losses in feet of liquid.
RE: PUMP NPSHA
The graph shown in this figure is abstracted from the Hydraulics Institute standards, which may perhaps have more information.
RE: PUMP NPSHA
Required: To calculate Npsha for propane to same datum. Point is to calculate this from the 9.7 ft for ethylene, with somewhat minimal calculations, rather than from scratch (in other words, consider the fairly large difference in vapor pressure of the two liquids, propane higher than ethylene)
And ARTISI and BIMR Please just stay at home, enough folks in the world quoting from Aesop's fables thank you
RE: PUMP NPSHA
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: PUMP NPSHA
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: PUMP NPSHA
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: PUMP NPSHA
no more correspondence with you two!
RE: PUMP NPSHA
Keep in mind that nobody here is paid for the help he/she provides. Everybody does that for free. You can ask for help but you have no claim to it. And your initial request to get a respond the same day and to tell you how to contact somebody directly without is/her approval was anything else than polite.
RE: PUMP NPSHA
RE: PUMP NPSHA
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: PUMP NPSHA
I looked up your posting history and you've been around long enough and asked enough question to surely understand how this site works.
Your question might be about NPSHA, but people with experience are also noting that the NPSHR might also change.
Your question seems to ignore the initial pressure on top of the liquid and unless your piping system is short and easy to measure, the impact of different fluid viscosity on the friction drop.
your data is all over the place as presented here and I can't see what the difference is between your VP between liquids at whatever temperature you're working at.
Basic answer to your first question - Is there a rule of thumb - No
Last question you posed - Yes it does.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: PUMP NPSHA
You might check into a stint in Charm School as well.
RE: PUMP NPSHA
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: PUMP NPSHA