Can I mount a gage PT above a liquid process tap.

Ideally, you want the PT below the pipe. With the PT mounted 7.5 ft higher, keep the following in mind:

Slope any horizontal runs up toward the PT to aid in venting. Not sure offhand, but 1/8"/ft would not be unreasonable. (some may call this overkill)

Apply head correction to the PT calibration (zero output higher by 7.5 ft H2O)

Purge air out of the lines with the pump on.

Realize that if you have the slightest leak at the transmitter, you may lose your impulse piping fill, causing the PT to read higher than normal.

Realize that if the HC is insignificant compared to the range of the PT, then air in the impulse line will cause insignificant errors. And vice versa.

Good luck-

mkruger21,

Thanks for the help.

Just to make sure I follow you, the PT range in this case is -14psi to 300psi, the expected system pressure fluctuation is 45psi to 110psi, and the HC (i'm still learning here so i assumed you were talking about head correction) would be 3.25psi(7.5 ft H2O).

So in this case, even if the impulse piping becomes filled with air, errors will be insignificant. Correct???

Thanks!

Your potential HC error is 3.25/314 = 1.04% full scale.

To me, that sounds insignificant based on the description of your system. If you correct for head, and your line stays full, then 1% saved is 1% earned.

Beg to differ,

If the impulse piping has air ingress when the pump is off, it will leak the air back out soon enough when running again.

For your measurement range, not a problem.

Just make sure you compensate correctly (10 kPa/m, 0.435 psi/ft) and maintain a 1:10 slope.

Your point about the bidirectional leak is well taken. Thanks.