vacuum test digester tank 1

[ilovepoop]

I need to vacuum test a WWTP digester tank to 3 inches water column vacuum.

My tank is 82' diameter with a base(irregular sump drains) of 16,200cf, main wall area of 456,807cf and a upper area of ~14356cf.

My problem is im specced 3 inches of water column vacuum, and my tank will be filled to el 112 meaning I have 14356cf of STP air at the top and the rest water.

How much water do I have to pump out to reach the vacuum conditions?

 

[ilovepoop]

to be more specific, disregarding the irregular bottom, the tank walls are 85' with water. Im less asking for a final elevation and more asking what steps I need to find the final elevation.

 

[1503-44]

3" of water is 3/12 × 62.4/144 = 0.1 PSI pressure reduction
Assuming initial pressure is 14.696 psia std atmospheric pressure at sea level and 69°F
14365 cf x 14.696 = 14.596 x v2
V2 = 14463cf
14463 - 14365 = 98,4cf

Close off the tank.
Remove 98.4cf of water
Volume of air will expand from 14365cf to 14463cf
Pressure will reduce to 14.596 psia

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

The problem with that method is that you are only testing the section of the tank above the water level.

You need to test the tank empty IMO.

Get an accurate guage and a venturi type ejector.

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

 

[1503-44]

Great point LI. I didn't see it.
Well done.
--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[ilovepoop]

Thank you for the replies LI and 1503.

LI, that is correct I only need to vacuum test the gas dome above the water level.

The tank is already going to be filled for hydrostatic test.

 

[1503-44]

We suggest that you test the bottom of the tank (i.e. the entire tank) for vacuum pressures.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."