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# Pressure in a Oil Damper

## Pressure in a Oil Damper

(OP)
If I have a double rod-end cylinder, fill it with oil, and connect both ends together via a needle valve, then start applying force to the rod in order to push/pull the pistion, is there any pressure difference acorss the valve when the needle valve is fully open? If so how can I calculate it? Is the pressure independent from the applied force?

Thanks

### RE: Pressure in a Oil Damper

Even if the needle valve is fully open you most likely still have some pressure drop, depending on the flow. Even with the valve open you have to consider the fittings, hose/line, needle valve body, etc. The pressure will be a function of flow and restriction. ISZ

### RE: Pressure in a Oil Damper

You need to know the valve pressure/flow characteristics for various valve openings.  Calculate pressure drop vs flow rate.
Relate flow rate to piston speed.
Relate piston force to pressure.
Then you will know the relation of piston force to piston speed for various valve openings.

Ted

### RE: Pressure in a Oil Damper

(OP)
Thanks Ted and ISZ.
OK there is pressure drop due to the valve structure, fittings, hose/line.
The problem is I want to choose a right valve for my system, and I do not know about my valve yet.
Let me ask my question this way: in an ideal (unrealistic)situation If there is no head loss across the valve due to the friction etc, is there any pressure difference between two ends of the cylinder when I am moving the piston?
Please note that there is no pump in the circuit and the system is totally passive (driving force is applied to the rod)

### RE: Pressure in a Oil Damper

In your unrealistic case, very little.  Flow does move from high pressure to low pessure and with no flow losses this difference would be very small.  An ideal, frictionless condition.  Therefore, essentially no damping.

Ted

### RE: Pressure in a Oil Damper

There may be inertial forces that so far are being neglected.  Acceleration of the fluid; acceleration of the piston.

Ted

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