How to pressurize a system with air to find leak?

baj702

I have a leak somewhere, about 1g/day (2 pipe steam/575 GROSS BTU boiler/16 unit apt building)

I've replaced the boiler and all the piping in the boiler room. I've replaced about 150' (2/3) of the steam main. I've replaced 3/4 of the radiator valves and have checked all the others for leaks.

The return is off the ground and dumps into a condensate tank.

I started with over 3g/day loss, and I've gotten it down bit by bit, but I can't get this last 1g. I'm thinking I need to pressurize the system and listen for a whistle.

1. What pressure can I go up to?
2. Will the steam traps on the radiators be OK?
3. Do I need to take off the F&T traps, sight glass on boiler...?
3. Will the main and returns both be pressurized? e.g. will the pressure work its way through the radiator steam traps and pressurize the return?
4. Any advice?

nicholas bonham-carter

Could this be the type of vapor system, which vented the air into a chimney? If the pressure is too high, then whatever device would have kept the steam in may have become overpowered.
Have the returns been replaced, as they are more prone to rust out than the supplies.--NBC

Sailah

Steam traps won't care at all if you pressurize but they will be open so air will flow freely.

EBEBRATT-Ed

Check for any steam coming out the vent on the condensate tank. Losing steam is losing water. You could have some bad traps passing steam. Even a small wisp of steam. Check the vent at the end of a long burner cycle

JUGHNE

Have you located all of the F&T traps?
Any number of them could be passing steam that is venting out the cond pump as Ed said.

What pressure does it run at?

baj702

@nicholas bonham-carter The boiler runs at between .5 and 1.5 psi, and spends most of its time at around 1 psi. The returns haven't been replace because they've looked good everywhere I've checked. They are suspended off the ground, so they haven't had the chance to rust out from sitting in wet mud or something. The supplies rusted out (one hole I could put my hand through!!) because they were sitting in the dirt.

@EBEBRATT-Ed I've checked and rechecked the condensate tank and vent. I piped a long vent that traverses back and forth with a slow rise to make sure any residual steam coming out of there would condense and flow back into the tank.

@JUGHNE The F&T trap before the condensate tank is new, and I've never seen any steam coming out of the condensate tank (for example, if I remove the vent pipe so any steam can just go right out the 2" hole at the top of tank - I haven't seen any steam). The boiler is running at between .5 and 1.5 psi, with most of the time spent around 1psi.