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Question: liquid pressure
2

thread135-478695

Question: liquid pressure

Question: liquid pressure

(OP)
Hi community!
sorry, this may be a stupid question :D and not sure where to post it..

I have the following case: a tank with a pipe connected to its bottom, closed with a plug is partially filled with a liquid (red); the tank is pressurized with compressed air (light blue) from its top, let's say at 8 bar.
Valve at the bottom is opened, so the pipe is filled with liquid.
In this situation the manometer will read 8 bar.

Now, I'm closing the valve and I'm depressurizing the tank from the top: I have atmospheric pressure in the tank now.

What value the manometer will read? I think still 8 bar?

RE: Question: liquid pressure

You would need to add the pressure from the liquid column to that pressure, but essentially yes you are correct. If the valve is closed (isolates the pipe) and the conditions on that side of the valve remain unchanged, the pressure would remain the same regardless of what you do on the tank side.

Andrew H.
www.MotoTribology.com

RE: Question: liquid pressure

Your pressure guage (Manometer) will initially read 8 bar PLUS the pressure created by the head of the liquid from liquid level to pressure guage.

So it will be more than 8 bar.

If you then isolate the bottom section this will stay at 8 bar providing there is ZERO leakage across the valve or change in temperature. Any losses of fluid will reduce pressure, any positive change in temperature will increase pressure

Remember - More details = better answers
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RE: Question: liquid pressure

(OP)
Perfect, thanks, yes, considering no leakage and yes I didn't consider the head as it's negligible.

RE: Question: liquid pressure

Hi ,
What you will be reading is a gauge pressure ! be specific about the unit absolute or effective.
my 2 cents.
Pierre

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