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Calculate CFM for exhaust from vacuum pump

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cityjack

Mechanical
Mar 5, 2013
50
Afternoon all,

I have a liquid ring vacuum pump that is pulling 17in/Hg. I exhaust into a separator tank. But the exhaust from the separator tank needs to be scrubbed before it can go outside. My scrubber mfr. needs to know the flow rate of the exhaust. Can I calculate that without having to use an anemometer?

Thank you.

Sid
 
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You can try the formula below, to get some ballpark estimate.

Q = (V/t)ln(P0/P1)

Q - Volumetric flow rate
V - Volume including piping
P0 - Initial pressure, atmospheric
P1 - Final pressure (abs)


If you know the volume then note down the time it takes for lowering pressure from P0 to P1 and then you can calculate gas flowrate.


 
quark's formula assumes you are just pumping gases. If there is evaporation taking place in the pumped chamber, then you need to account for that. You could also look at the outflow volume, yes an anemometer plus temperature (and knowledge of the output gas composition)...or stick a standard 30-gallon garbage bag on the outlet and time how long for it to inflate...
 
I would assume the worst case is when the vessel or pipe or whatever is at atmospheric conditions when you first turn it on.

After that depends on what you are pulling out of the vacuum.

Does the vacuum pump vendor not tell you?

I wouldn't have thought your vacuum pump would like any sort of back pressure above atmospheric though or does the exhaust from the separator work at a very low pressure / separate pump?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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