How much pressure - negative OR positive - should be immediately downstream of a trap?

ariccio · January 2

I'm asking specifically about a low pressure steam system with vacuum return.

Immediately downstream and downstream of a trap, should the measurable pressure be positive or negative with respect to atmospheric? What about if the trap is failed open?

It's the age old story, a coop building that never replaces failed-open traps, but *now* there's also water damage in my apartment.

I would not be surprised to find pressure in the returns, even though we only have a leak when the radiator is on. But I also do not like to assume, I like to measure.

109A_5 · January 2

Not sure how the pressure is relevant, maybe just repair the leak. When the radiator is on there is steam, steam turns into condensate, leaks let the condensate out of the system.

mattmia2 · January 2

in a 2 pipe system everything around a radiator should be sealed, if something is escaping that is a separate issue from the system issues.

Jamie Hall · January 2

You mention that this is a vacuum system? How is the vacuum created and maintained? That will determine the correct pressure downstream of a trap, which should be very close to the pressure at the vacuum source.

In an atmospheric two pipe system, the pressure in the returns downstream of the traps should be at or very very close to 0 psig. That said, again in a two pipe atmospheric system you won't see a pressure above atmospheric by much (half an inch of water column, maybe) as any steam escaping a failed trap will condense almost immediately. The exception will be if the failure is complete, or if there are several failures, and enough steam gets by to close the vents on the returns. In that case the pressure will rise and may be near the pressure in the mains.

How much pressure - negative OR positive - should be immediately downstream of a trap?

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