Old Hoffman Vapor Vacuum System

Matthew Aldrich

I have an old Hoffman Specialty steam heating system which was originally designed to operate with a vacuum - vapor vacuum is the term Hoffman used. It is a two pipe system which originally had a main vent which would not allow air back into the system - essentially maintaining a vacuum. It now has a gas-fired boiler, so I have disabled the vacuum feature on the main vent. The system does have a Hoffman Differential Loop which is suppose to ensure differential in the pressure between the supply and return lines. All of the traps - all 25 of them have been replaced and are operating properly. I have one problem - one radiator on the 3rd floor still will not heat up. It sounds like the steam is condensing before it reaches the 3rd floor (hear gurgling in the walls for that one radiator). That radiators supply line is in an interior wall and insulated as far as I know. It is in the middle of the main supply line. The other 3rd floor radiator (on a different supply line) is working. The system is operating at about 1-2psi. Would the Differential Loop cause any problems - all of the old diagrams I saw showed the loop in a vacuum system? Any other ideas on the cause of the problem.

Mad Dog_2

Not if all the others are heating fine

It could be the return on that rad...even though you have a new trap...it could have some gunk impedeing flow out of rad. Mad dog

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Steamhead (in transit)

But if it's gurgling

it's probably coming from the steam line to that rad. I bet there's water collecting where the pipe has lost its pitch.

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gerry gill

The system should only

be run in ounces or the steam blows thru the dif. loop and closes the air vent...but like Mad Dog says, you may have a pipe issue..i've found gurgling usually indicates a bad pitch on a pipe..

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gerry gill

yup, yup..i agree



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Matthew Aldrich

Thanks

Thanks for the help! I had thought it might be a pitch problem on the steam main after looking at the way the pipe is running up from the basement. I think the return is fine as I ran the system with the steam trap open on the return and the radiator still did not fill.

Related to the Hoffman Differential, I did a bit of reading and it seems to be fine (just need to get a vaporstat to run the system at oz versus pds).

Thanks again for the info!