Hidden Restriction In Two-Pipe Vapor Steam Radiator

Gordo

For your enjoyment, a real-time FLIR-One video of a 1920s Hoffman System two-pipe vapor radiator heating up.

Notice something strange?

The incoming temperature on the supply pipe and the Hoffman #47 valve reads "205* F", but the temperature emitted at the radiator downstream from the valve (which is fully open) is significantly lower, some 150*F or so.

Why is this, you ask?

Please watch the video until the end to see the reason (the last 30 seconds are filmed in normal light and were filmed BEFORE the FLIR video!).

https://www.youtube.com/watch?v=1wfE9AQ5zJQ

Jamie Hall

Neat! Thanks @Gordo .

gerry gill

Hi Gordo..what was the purpose of the restrictor plate when the radiator has a trap? Was the rad stealing to much steam without it?

Jamie Hall

I wasn't going to ask that... since that Hoffman valve should be adjustable, too?

Gordo

@gerry gill: I don't have a good answer to your question, just a few guesses and observations.

The Hoffman #47 was not really designed as a modulating/restricting valve like the famous #7. It is really just a fancy on-off valve.

It's only "advanced" feature was a better designed "packless" system to provide a tighter seal under vacuum. So I suppose the built-in restricter plate kept the steam away from the trap under almost all but the most extreme pressure conditions.

In this case, I would posit that it is doing it too well. The hole is too small for a 1/2 psi system. The boiler (installed by others) short-cycles at 10 oz/in2.

The trap was there as a suspender for the orifice belt.

None of the Hoffman literature I have even mentions the availability of Hoffman radiator restricter valve spuds, so it may have been a unique mix-n-match! The only thing close was a separate orifice plate with an adjustable feature that was available circa 1935.

I know other manufacturers offered these type of radiator spuds, so if anybody knows more about this, please share.

I do not know what the original traps were on this system, as they had been replaced with Hoffman new-type #17Cs when we got there.

They may have been the really cheesy Hoffman #18, so an aggressive restriction would have been required to get through the warranty period.

I

JUGHNE

My 1955 school has those same valves with 17C traps.
A separate copper orifice plate was in most of the spud unions.
All traps were original and may have been functional. But the amount of bookshelf demo required warranted changing all the elements during the summer.
I replaced some deteriorated orifices and now wish I would have downsized all of them as the thermal envelope has improved.
The valve does a fair to lousy job of regulating the flow.
These were 1" or 1 1/4" steel fin tube convectors.
Was a new coal burner fire tube steam boiler at that time.
FWIW

Steamhead

This is the system that radiator is on. There was a leak in the steam pipe under the rad, that's why we were there. We replaced the pipe and corrected the pitch on the return from that rad, and repitched several rads.

https://forum.heatinghelp.com/discussion/161687/repiping-a-columbia

The Steam Whisperer

I suspect those plates are in there to help improve heating balance. I have seen them on the valve side before in vintage Dunham valves on a pumped vacuum system with radiator traps. That radiator looks like it about 32 EDR, and for a 1/2 psi pressure drop at the orifice, the orifice size would be 7/32 inch... so it looks about right. With these orifice systems, there is almost no need for a pick up factor, in fact sizing the boiler to the heat loss plus about 10% for piping losses seems to make more sense. I run boilers on orifice systems down to about 20% of typical radiation load and still provide even heating to large buildings ( depending on system configuration).
I don't think the restrictors need to come out, I bet the boiler needs to be downfired. I'd figure out the heat load of the building and start from there.

jumper

Can we conclude that we don't need no stinking steam traps?

The Steam Whisperer

If the orifices are sized right and the boiler pressure is properly controlled, no traps are necessary at standard free standing radiation. Look up the Moline Vapor/Vacuum system to get the idea.

PMJ

jumper said:

Can we conclude that we don't need no stinking steam traps?

I have concluded that. Rads never need to be full to match the heat loss so steam never needs to get to a where a trap goes.

Gordo

On this system, it appears that the boiler was way over-sized (by "others") and has already been down-fired to max limits.

It still short cycles.

The other issue may be the new Hoffman #17Cs on all the radiators on this system (again, installed by "others") with their infamous "durastats". I say infamous, because as Mr. @gerry gill has taught us, that particular trap element is notoriously restrictive to air flow.

In the customer's large kitchen, with its small radiator, I enlarged the orifice 1/32 of an inch and the temperature differential, as measured by the FLIR-One, was 15*F less than the radiator shown above (205*F in, 165*F out).

gerry gill

We had a radiator one time on a Mouat water seal system that keep blowing thru regardless of how the valve was adjusted (little powder room rad) so Steve put a an old copper penny into the stub and soldered it in and then drilled an orifice thru the penny. Worked brilliantly.