Pressure Testing 2

[Seaya]

I have to over pressure and leak test a duct. I am enclosing each end of the duct to pressure test to an internal presuure of 4" WC (0.14 PSI) gauge. Here lies my question, will I have to pull a partial vacuum or apply positve air pressure to the enclosured space? It appears that I would have to add air pressure but my thoughts are clouded with the effects of atmospheric pressure.

 

[DRWeig]

Seaya,

You're only concerned with differential pressure between the inside and outside of the duct, correct?

The outside (ambient) pressure doesn't matter, as long as the inside is 4" WC higher.

Good on ya,

Goober Dave

 

[metengr]

Agree. A postive internal pressure test for ducts is much easier to evaluate leaks at joints than pulling partial vacuum.

 

[Seaya]

Correct, all openings to the duct will be sealed except for my supply connection to feed or extract air pressure.

 

[rb1957]

doesn't the gauge measure the pressure relative to the local airpressure ? (hence the term "gauge pressure")

 

[JohnGP]

Yes, but for such low pressures I have just used a simple manometer - plastic tube on a board, and pressured up until the difference in levels equals the differential pressure required - 4" WC in this case.
Cheers,
John