Pump possible cavitation problem

[LeitoGM]

Hello All,

So, I was informed that putting a wall mount heat exchanger that consists of a motor, pump, filter and a heat exchanger that runs at 8.5 gpm would cause cavitation of the pump, since the gearbox only holds 4 gallons of oil (plus the oil that would compensate for the volume of the new heat exchanger).

I tried googling the possible causes of the phenomenon, but was unable to find any info. I would imagine that the pump runs so fast that it starts pulling air bubbles into the fluid. However, is there like a calculation or a website that shows more info regarding this matter?

Thank you all.

 

[tbuelna]

You can experience cavitation in any part of your system if the conditions are right. Your flow rate of 8.5 gpm with a fluid volume of 4+ gallons is a turnover rate of around 2X/min, which is not too bad. In order to reduce the potential for cavitation at your pump inlet, you need to minimize the amount of entrained air in the fluid feeding the pump. You also need to make sure the pump inlet/outlet flow velocities are suitable.

 

[someguy79]

Air entrainment can show symptoms similar to cavitation, including reduced pumping capacity and noise. It would be good to try to purge air from the system if that's the case. Look at high points in the system and see if you can get it out of there.

If you really have cavitation happening, that means a bit of your fluid is changing from liquid to gas phase and then quickly back into liquid.

If you want to calculate this, you'll need the vapor pressure, density, and viscosity of you liquid at operating temperature, and a bunch of info about the system configuration. (pipe sizes, bends roughness, etc.)

Cavitation happens in pumps that have insufficient NPSH available or run out at the extremes of the pump curve. A good reference for this would be HI 9.6.1, though most major pump manufacturers have a guidebook giving a lot of the same info. I just don't like to rely on manufacturer info too much.

Example:

http://net.grundfos.com/doc/webnet/mining/_downloads/pump-handbook.pdf

I'm assuming this is a centrifugal pump of some kind.