Vacuum Pump flow/leak rate

[AlwaysConfused1]

All,

I have a small vessel that I suspect (know) is leaking. I anticipate the leak rate to be higher the higher the pressure is inside the tank. What I wanted to do with the equipment I have was connect the vessel up to a small pump and pull a vacuum inside the vessel and have a ball valve between the pump and vessel so that I could control the flow.

I was thinking I could hook up an orifice flow meter to the exit of the pump (so that my differential pressure transducer would not be under vacuum) to determine the flow rate. The problem I am having a hard time understand is how I would determine the leak rate given those parameters. Having the pump in the middle of the system (between the flow meter and the vessel is messing with my head.

Can anyone help me wrap my head around this?

 

[Latexman]

You don’t need a meter, just a good pressure gauge and the right differential equation.

P = m.R.T/(MW.V)

dP/dt = R.T/(MW.V) x dm/dt

Good luck,
Latexman

Engineers helping Engineers

 

[quark]

Why can't you do a simple pressure test of the vessel and quantify the leak rate over a period by isothermal equation? Calculating leak rate from a vessel using a pump is beyond my imagination.

 

[LittleInch]

Two things.

Not all vessels can withstand external pressure and can collapse spectacularly.

You can't work it out because it doesn't make sense.

It can only work a bit if the vessel is gas filled and you create a lower pressure which eventually stabilizes. Then in theory to maintain the lower pressure the air mass out from the vacuum pump will equal the amount entering. However reversing the pressure differential might increase the total leak rate.

But you should be able t do the same in revers, i.e. pressure it to a fixed value and measure the amount you need to inject to maintain that fixed pressure


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