#3 Hoffman Air Line Valve

John Gorjanc

I ran into a one-pipe steam system that is not heating evenly. Classic case of cranking the pressuretrol cut-in and cut-out too high (will replace with a vaporstat).

Each radiator has a Hoffman #3 air line valve. The outlet vent is piped in 1/4" down to the basement and into the dry return which has a main vent on it.

Only the first couple sections on each radiator are heating - even though the boiler is continuously cycling. Obviously the #3's are not venting and the air in the radiator is compressing as the steam behind it is pushing.

My old Hoffman Data Book from 1934 has the specs for the #3 air line valve. It shows a maximum operating pressure of 10psi. It doesn't show the drop-away pressure. It mentions something about the valve being wide open when cool and shut tight when hot (when steam hits it).

Are these old #3's the same as #1A's and #40's in that even though they're cool (no steam) they still won't drop away and allow further venting until the pressure drops below their "operating pressure"?

Even so, can these #3 Hoffmans still be working after 70 years? Can the thermostatic diaghrams still work after a zillion cycles? Are they still available or are they long gone?

I could replace them with #1A or #40, but then I'd lose that beautiful 1/4" vent piping that takes the hissing and spitting out of the rooms and down to the basement.

Whad'ya think?

John

scrook_2

Hoffmann #3

They list this as a thermostatic only (no float) air vent, 25 psi max, 1/8" male inlet, 1/4" male outlet for air lines and "Paul systems" (whatever that is). A #1A or a #40 (or a Gorton) shouldn't hiss or spit though, but you could buy new #3's too.

http://www.hoffmanspecialty.com/pdf/hs900/HS900-3474.pdf

Crank the p-trol down to 1 to 1.5 psi cutout (or as low as it'll go), and check the main vents too, maybe they're shot.

Unknown

Paul system

They were before radiator traps, but after manual cocks on the radiators.

The paul system had 1/4" tubing running back to the basement to a common pipe to vent the air, and in the old days, a venturi ejector pulled the air out using waste steam. There probably was a generator running on steam, there, at one time.

Noel

Steamhead

You need (Hey Boilerpro)

some sort of ejector to pull the air thru those lines. The Paul system won't work right with just a main vent. It has to have suction on those air lines.

It's possible to build a steam-powered ejector out of pipe fittings. The air would go out a main vent and the steam would condense and could be directed back to the boiler. Dave "Boilerpro" had some ideas on that a while back- ya listenin, BP?

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Boilerpro_3

Now I am,

thanks for the heads up Steamhead! Take a look at how the Moline Systems operated, and this may give you an idea as to how to get this system running with vacumn on the returns. I haven't had nearly the experience with steam as many of the first rate contractors here (like Steamhead), but I have run into a few Moline systems and are fascinated by thier elegant simplicity and exceptional performance. Vacumn was generated in this two pipe, orifice supply valve type system in the returns with a steam powered venturi. This was located at the end of the steam main and was connected to a main vent type device that also closed on vacumn. The system is piped reverse return, so all radiators on the system would get an equal push from the steam boiler, or suction from the return line. On startup, the venturi allowed the mains to vent and, as the air passed through the venturi air was drawm out of the radiators. Then, when the mains were vented of air, the steam passing through the venturi would also create vacumn on the return lines. The steam and air that passed through the venturi device would go into some type of condensor, either a long pipe at the basement ceiling or a radiator.... so don't insulate this pipe! The steam would condense and then drain back into the boiler wet return lines. By keeping the steam pressure low and with the limited amount of steam that could pass through the venturi, steam would never make it to the end of the condensor. Others (Noel) here have found that with the on/off nature of newer steam boilers, the main vent should no longer be a vacumn vent (Hoffman still has these in thier catalog). These systems seem to operate best at just a few ounces of pressure without the whole system going into vacumn, so a vaporstat is a real good idea.

A venturi should be fairly easy to obtain and the cross section of the opening probably should be sized based on the orifice plate tables available from various manufacturers (Turnstall?). This will give you the size of condensor you need. I haven't tried this yet, but a monoflow tee from a hot water system may do the trick as the venturi device. This idea came from a very sharp friend in the industry.....it's not my own. I'd be real curious to see what you end up with.

This set up would sure beat the cost of a vacumn pump and has no moving parts to wear out. It would be a great system to us a condensing steam boiler (since the system could run at temps as low as 140 to 160F) with a fully modulating burner, then the system could be run at vacumn, assuming its reasonably tight. Noel and Bill from Honeywell have spoken about modulating burners on steam, and there are condensing steam boilers out there, but not sure in what sizes.

Boilerpro

Woody

intersestingly

enough, we came up with a solution to controlling this Paul system that still works fine today. going back to the late seventies we were approached with similar control issues. after research on the system we found that the hoffma or dunham air line vent acted just like a miniature steam trap! with no steam in the system, the air line pump would suck the air out of the rads to be replaced with steam at which time they'd close and open to expel air but no steam. these units are located three quarters of the way up the rad so no condensate would get into the return lines etc. we decided to install a macon trv on this return line and low and behold we were able to control the venting which in turn controlled the amount of steam that got into the rad and bingo! worked fine then and still working fine today! hope this helps someone. tp tunstall

Unknown

TP, did you use vacuum with that?

or did I miss something?

Noel

Woody

noel..

what we did was put vacuum breakers on the main risers (not vents), and this let the system operate as a one pipe system. we put the vacuum breakers also at the top of the risers. so we had a macon valve that controlled the thermostatic vent by controlling sensing the air temperature in the room and when the system went down to atmospheric the vacuum breakers would let the air in and condensate return etc etc... dartmouth college...bob broderick (retired now ) just plain old fun..

Unknown

They were our neighbors.

I was at Colby Sawyer College, 30 miles away. We were a nursing school that worked with Dartmouth Hitchcock hospital, among others.

I never got up there to see their district system. So close, too.

Noel

Woody

i remember

well! they (colby sawyer and dartmouth ) have been using the macon valves and tunstall capsules for years and have been delighted! thanks noel. tp

Unknown

3 buildings full of Macon valves.

> well! they (colby sawyer and dartmouth ) have

> been using the macon valves and tunstall capsules

> for years and have been delighted! thanks noel.

> tp

Unknown

3 buildings full of Macon valves.

They are building a new building right now.

Noel