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Instantaneous Pressure of a System

Instantaneous Pressure of a System

Instantaneous Pressure of a System

(OP)
I have a fluid vessel with fluctuating pressure that controls a pilot operated valve that is approximately 3 feet away from the system.  I am looking at moving the pilot operated valve an additional 2 feet away due to equipment reconfiguration.  It is my belief, regardless the length of the connecting tube, that the pilot pressure relative to the pressure vessel timing is almost instantaneous (in milliseconds) and the pressure output to the pilot valve would not change as long as the elevation does not.  Can anyone recommend a reference or principle that I could use to back my decision.

RE: Instantaneous Pressure of a System

High school physics -- the hydraulics chapter.  The pressure in a contained fluid is the same throughout the container [ignoring static head pressure].  Any applied pressure is uniformly distributed evenly throughout the system.

RE: Instantaneous Pressure of a System

Responses to transients are a bit more complicated than that.  Two aspects to look at:

Changes in pressure propogate at the speed of sound (whatever that happens to be in the fluid you are using, under the conditions you are using it) - by definition.  Once you know the speed of sound and the additional path length, you have the additional propogation delay.

You also need to think about how much fluid needs to enter the sensing element of the valve for it to register a given change in pressure.  You will need to move the entire contents of your connecting tube by the corresponding distance.  The longer your tube, the greater the mass you will have to shift and the greater the viscous drag (with the driving force governed only by the diameter of the tube) and so the longer it will take to push enough fluid into the valve to open it.

A.

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