Hydraulic Servo Valve

[Mohamed Saner]

Hi,
I have an inquiry about servo valves, what is the drawbacks if the drain port to the tank been plugged??

 

[BrianE22]

Oil that has leaked from the valve will now not have zero back pressure. That back pressure could cause problems with the valve operation.

 

[3DDave]

On hydraulic motors that results in blowing the main seals out of the motor with serious amounts of leakage. It depends on how the valve is built but the drain is there to prevent full system pressure from doing damage. If it would do no damage they would not have the drain line.

 

[zeusfaber]

Regardless of the exact technology used, the drain line carries away the fluid that flows through the first stage of the valve. It is this flow that creates the pressure drop in the first stage which in turn creates the pressure difference to position the second stage of the valve.

If you block the drain line, there's no first stage flow and no pressure drop so both sides of the first stage output pressurise up to servo pressure, regardless of first stage position. At this point, you have lost control of the second stage.

A.

 

[Mohamed Saner]

Thanks zeusfaber, will the valve been damage at this case??

 

[zeusfaber]

I imagine it depends on the type of servovalve you're using and how the actual supply pressure compares with the rated pressure. It's not unusual to see servovalves used at much lower pressures than they're rated for. Looking at some of the valves I use, I don't think the casing around the jet-pipe stage would stand up to the full rated supply pressure. Given the price we pay for the things, it's not something I'd try out just to see either.

A.