Effect on atm pressure for Cavitation

[whizzz]

Any comments for relation between fluid temperature and atmospheric pressure to Cavitaion. if the pump used at sea level, there must be a different with the pump used at high altitude (on top of the hill). The water boiling temperature also will be change. Is it can be the effect in pump perfoemance?

 

[Artisi]

Yes.

Naresuan University
Phitsanulok
Thailand

 

[Artisi]

NPSHa= Ha, - Hvpa, (+)/(-) Hst, - Hfs.
Ha = Absolute pressure - (function of barametric pressure)
Hvpa = vapour pressure - (function of liquid temp.)
Hst = product level from pump centre line -(either + or - )
Hfs = all suction losses - (function of friction etc)

Naresuan University
Phitsanulok
Thailand

 

[whizzz]

how big is the effect?

 

[Bjegovic]

not too big. don't bother to think about it in most normal applications. (hope your pumps are not on the top of the world!)

 

[whizzz]

because now my pump operating at 5600ft from sea level and we found a cavitation occured. just want to relate it with atm pressure
tq

 

[Ashereng]

Are you thinking that an elevation change is the only cause of the cavitation?

 

[bulkhandling]

Barometric pressure at 5600 ft elevation is 27.7 ft comparing to sea level 34 ft.

 

[Artisi]

As you can see by the figures from bulkhandling, you have lost 6ft.of NPSHa before you even start looking at inlet loss, suction lift etc.That is not to say that atmospheric is the only cause of your cavitation, you need to calculate the inlet losses.

Naresuan University
Phitsanulok
Thailand

 

[whizzz]

Yes i know that the atmospheric is not only the cause, just want to confirm the effect. Any comments on water temperature? is it also one of the source of the cavitation at this level?
TQ for all the comments

 

[Artisi]

what is the temp. of the water you are pumping?

Naresuan University
Phitsanulok
Thailand

 

[WebWizz]

Looked at the first response from Artisi, which is pretty good. As long as there is enough margin between NPSH_available and NPSH_required the pump should work OK. The vapour pressure of the liquid is a function of temperature, the problem with a high altitude is that the pressure and therefor also the NPSH_available is less.

Best thing to do is calculate it. Good website to use is

http://www.engineeringpage.com

> Pumps > Pump conditions. Helps to calculate the NPSH_a.

If you need the vapour pressure you can use the curve that the physical properties database provides on the same site. Alternatively the steam tables will do the job.


Best regards, Wim

 

[whizzz]

the water temperature measured here is about 16 deg Celcius

 

[Artisi]

The VPa for water at 16C is less than 1psia - therefore this is not your problem.

My suggestion is you do some reasearch / learning on the subject, a good place to start is with this site.

http://www.mcnallyinstitute.com/index.html

Naresuan University
Phitsanulok
Thailand

 

[whizzz]

tq