Hydraulic valves

Hi,

Can anybody please guide me, what are selection criteria for hydraulic valves over pneumatic valves? In which situation they are preferred? Is there any international standard for selection of hydraulic valves?

Thanks in advance.

Hi instruguy,
In 40 years I have rarely seen hydraulic actuators used unless it's a water control valve using the line pressure as the driving force(check out Singer or Clayton).

Hydraulics requires a source of HP fluid e.g. motorized gear pump, oil tank filters etc. wheras in most cases air pressure is available.

The systems I have seen have been dedicated to a single specialized valve or packaged system operating at very high line pressure where the force required would call for a huge pneumatic actuator.

Don't forget electric actuators, some of the newer ones incorporating stepper motor drives are very good but again usually only where air is not available. Electric damper actuators are very common.

In my oppinion.
Start with air (unless you are dealing with large water valves, in which case water powered), Electric if no air, Hydraulic only in special cases.

I am not aware of a standard.

Hope this helps
Roy

Hi Roy

Thanks a lot.

Hi Roy,

Are you familiar with water-powered hydraulic valves used in old water pumping stations to automatically open/close the pump check valve at a certain pressure setting? If you do, can you share with me its piping schematic diagram and how it works? Also, I would like to know which valves need to opened/closed to open/close in the piping circuit to test/exercise the check valve. I know there is a dump valve on it which can be opened to close the check valve in the event of emergency. Thanks in advance.