Globe Valve

[mas26amin]

Hi,

we have used globe valve to reduce water pressure. we have tested the valve in below situation:
- piston pump to produce pressure up to 30 bar
- the pump include a pressure regulating valve so that we can adjust the outlet pressure
- then we have installed a globe valve
- after a globe valve, a gauge installed to show pressure

when the globe valve is completely open, the pressure is 20 bar. we close the globe valve to show the pressure 10 bar. we don't touch the valve anymore to see if the pressure is stable or not. however after some minutes the pressure reduce from 10 bar and reduce and reduce up to 3 bar!

we have tested with ball valve instead of globe valve, however the pressure remain constant during the time.

What is the problem with globe valve that the pressure doesn't remain constant during the time?

 

[LittleInch]

well the globe valve looks to be the wrong way around... The arrow seems to go from left to right, but your guage is supposed to be on the downstream side??

Globe valves are uni directional - they don't work well the wrong way round.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gerhardl]

Several factors will influence your pressure measurement and flow characteristic.

1) Factors as mentioned by LittleInch
2) The globe valve is probably not a regulating valve suited for pressure regulating
3) The pressure difference from 20 to 10 is so large that cavitation conditions can occur anyway
4) Turbulent conditions will occur after the valve, no straight pipeline stretch before gauge will give false readings
5) The flow might give too fast (or too low) speed in the line

If you want a constant regulated pressure below what the pump inbuilt regulation can give you, you need: a pipeline size suited to the intended flow and pressure, a straight stretch after the pumps regulation, a suitable pressure reducing valve dimensioned for the pressure and flow, a straight stretch after the reducing valve, a suitable and correctly mounted pressure gauge.