Where is steam pressure measured

Steamhead (in transit)

vacuum vents on the returns?

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Concerned Apartment Owner

Where is steam pressure actually measured

I'm new to this subject but also interested in it. I read in one of the posts that the Empire State building at a steam pressure of 1.5lbs to 2.0lbs. I'm curious to know if the steam pressure on a radiator on the 50th floor is at the same pressure as a radiator on the 5th floor. Second question. When using a vacuum system does this affect the overall pressure in the system.

Jamie Hall

the density

of steam is very low -- comparable to air or less -- so it doesn't matter where in the system you measure it; you won't see the difference on any normal pressure gauge. So the answer to your first question is yes, so far as you can measure. The answer to the second question is no; all steam systems nowadays run at a very slight positive pressure. In the good old days, with coal furnaces, vacuum systems did run at small vacuum when the coal fire was damped down. Takes special vents to do that, and you don't need it with oil or gas.

Concerned Apartment Owner

Thank you Jamie

That settles a question I've been thinking about.

RonWHC

Then how can numerous boilers

I service (& have installed) have 1-3# pressure on the boilers & 1-8" of vacuum on the returns? Why do caps on radiator traps resist lifting when they are disassembled for repair?

Vacuum systems still rock. And SUCK.

[Deleted User]

Frank.

If you're asking me - those jobs all have vacuum pumps w/ 1/2 to 5 HP motors driving them. Threw in my 2 cents to show there are few absolutes. Particularly in what we do.

Howsomever (sic). Hoffman still makes the #76 Vacuum Vent.