Cavitation issues in Recirculating loop with Pressure Sustaining Valve

[dsg1985]

Hi,

I've been tasked with designing a suitable setup for a vehicle washbay that draws water from a relatively small (~30kL) tank and pumps it to hoses and water cannons with operating points of 650kPa. The flow rates are ~20L/s for the cannons and ~2.5L/s for the hoses. The pump supplies 21L/s @ ~650kPa.

To keep the entire system at 650kPa I propose to use a loop recirculating from the pump back to the 30kL tank, with a pressure sustaining valve (set at ~650kPa) installed in the recirculating line.

The issue I have is that as there's basically just a short length of pipe running from the pressure sustaining valve to the tank, the entire 650kPa drop occurs across the PSV, leading to issues with cavitation. An orifice plate sized for 18L/s recirculating (just one hose running)will not be suitable for 3L/s recirculating (just one water cannon running).

The solution I'm considering currently is to use a differential pressure sustaining valve in line with the back pressure sustaining valve, that will provide a constant 200kPa (or similar) drop. According to the valve manufacturer, dropping from 6 bar to 2 bar, then having the remaining 2 bar drop across another valve will get us out of the woods as far as cavitation goes.

I'm concerned there will be issues with hunting if I opt for such a setup.

I'm not sure if I have the best solution (to be honest, my first 'project' as a graduate) and any advice would be appreciated.

 

[dsg1985]

I should have said an orifice plate in line with the pressure sustaining valve was the solution the valve manufacturer proposed, but I don't think it can be made to work with such a range of recirculating flow rates.

 

[BigInch]

You can check that using the valve's Cv coefficients over the range of flowrates you have in mind.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv