safe air pressure to test baseboard heating pipes?

bk9

I've got a gas fired boiler baseboard heating system with 3/4" copper piping. I've got a leak in a pipe in the slab. I want to test the other pipes in the same zone that are also in slab before I bother to reroute around the leaking pipe. What is a safe air pressure to test these pipes? Pipes are 60yrs old. The zone/loop in question is isolated from the boiler on both supply and return sides.

Jamie Hall

You need to go to twice what your pressure relief valve setting is.

hot_rod

I’d suggest 30 psi, that is what most boiler relief valves are set.

kcopp

Where 60 would be for sure and prob to the letter of the law... I would hate to see test and 60 and create a leak that wasnt an issue before...

Gilmorrie

Leak testing with compressed air is potentially dangerous. Because of the stored energy, a defective failure anywhere in the system can launch a lethal missile. Be careful and use the lowest pressure necessary.

Jamie Hall

To supplement my earlier comment -- all of the above. Plus a comment adding to @Gilmorrie 's remark: testing with water is much much safer, as he suggests. It is also a good bit easier in one major regard: Assuming there is no expansion tank involved, even a small leak will cause a significant and moderately rapid pressure drop, and variations in temperature (within normal comfort ranges) won't obscure the results.

bk9

Thanks.

Before I cut open the loop on either side of the leaking pipe buried in the slab, so I could pressure test both sides, I figured I'd see how quickly the entire loop with leaking pipe lost pressure. Using an air compressor, I charged the isolated zone (isolated from boiler and other piping) to 42 psi (42, and not 40 because 42 lined up with one of the marks on the pressure gauge), then sealed off the zone from the air compressor. Much to my surprise, it held 42 psi for 2 hours, then very slowly started dropping. After 24 hours, it's ~28 psi. I assume that large a drop for a zone that covers basement and ground floor of a split level single family is too much for it to be just copper pipe expansion?

kcopp said:

Where 60 would be for sure and prob to the letter of the law... I would hate to see test and 60 and create a leak that wasnt an issue before...

For sure, it's 60yr old pipe. I don't want to test the limits of all those old joints and the very thin walled spots that must exist.

Zman

I had a fire inspector once insist on a 300# on an older PVC system being remodeled. They did a double-take when I refused to be in the mechanical room when it came up to pressure.
In your case 30# will give you the info you need, Only go to 60# if required.

hot_rod

need to disconnect boiler and near boiler piping with expansion tank, if you test above 30 psi.

bk9

hot_rod said:

need to disconnect boiler and near boiler piping with expansion tank, if you test above 30 psi.

I isolated the loop from the expansion tank and boiler.

Any thoughts on the pressure drop I described a couple of posts up?