Two Pipe 36 Family with Hoffman 76

Ed. W.

Investigating a heat distribution problem, noticed Hoffman 76's (steam main vent, vacuum valve, float type). at third floor radiators. Could this be causing the problem? Any Ideas would be helpful.
Thanks,
Ed. W.

Steamhead

Nope. Someone was venting the risers. Is this a one-pipe or two-pipe system?

MilanD

Describe exactly what's the problem. Rad not heating? Those vacuum vents have not been in production for a long time so it's possible it is old and it went bad. If the system itself was not knuckleheaded over the years, new rad vent should fix the cold rad.

Danny Scully

Hoffman #76 is actually still produced @MilanD. Order it on SupplyHouse and you should have it by tomorrow

nicholas bonham-carter

The Hoffman #76 vacuum vent has a lower capacity than the 75, which is already slower than the Gorton #2, for a similar price.
Most of the main venting should take place on the horizontal mains in the basement, and any risers should be vented identically so as not to favor any one of them.
Since this is 36 units, the placement of the thermostat indoor sensor should be in the coldest upper corner of the building, so as to react first when the temperature drops, and don’t use setbacks.—NBC

MilanD

Danny Scully said:

Hoffman #76 is actually still produced @MilanD. Order it on SupplyHouse and you should have it by tomorrow

I stand corrected. OP said he noticed the vents on the 3rd floor radiators, not main - I was thinking vacuum vent on a 1-pipe rad.

As to 2 piper, Hoffman 76 on a rad? If this was a 2-piper, having it at the end of the dry return would indeed do wonders once the system heats for the first time.

Ed. W.

This is a two pipe as indicated in the Question. There are Two Hoffman 75's at the end of the main. Why 76's at the radiators, tree stories up? Can not figure this one out? Should I switch them to 75's?

MilanD

I've been distracted today... Been thinking on vacuum rad vents since you mentioned vacuum vent on a rad.

So what kind of 2 pipe is this? Are there traps at one side of a rad? Do all rads have vents? Is this a Hoffman or some other specific vapour system?

What's the history? Have these rads heated before and stopped heating recently?

nicholas bonham-carter

This may have been an old naturally induced vapor-vacuum system, and the correct place for vents would have been at the end of the returns, after the crossover traps. There would have been a main trap with float and check valve to let the air out and keep it out.
You may try going back to vacuum operation, if the system is tight. Such a system does not respond well to night time setbacks.—NBC

Ed. W.

There are traps at the end of each rad (17c). Only the third floor rads have 76s. These rads have heated before. There is no indication of a vapor system. I am going to double check for defective open traps in the system with my flir camera.

MilanD

Looks like you got it. There shouldn't be any vents there in the first place, so it looks like someone added those later. It still may work if they are vacuum and hold closed once steam hits them and don't open at all. I still can't picture #76 on a radiator tho. That thing is huge!

Fred

Somebody along the way, tried to vent those risers, using the 1/8" tapping (or maybe they tapped it to 1/4") on the radiator, rather than drill and tap the pipe where it comes out of the floor. It would probably work, as a vent but I suspect the steam probably raced across the radiator, heating only the top or bottom portion of it. I don't think they used the 76 for any purpose other than venting. It will open and close pretty much like the Hoffman #75 on a single pipe system. Probably what they had on hand or could easily get, at the time.