Return line in two pipe steam system

wam525

I've been trying to get rid of the water hammer noise in our 2 pipe steam system. I fixed a previous major remodel in the large kitchen where the radiators were moved and reconnected by a plumber with only hot water experience, so none of the pipes had proper slope. Now there is a residual occasional hammer on the other part of the house connected with a long sloped steam pipe. However the return line has no slope at all, and I'm wondering if it is needed for a return line. Also, about 50 feet from the boiler there is a strange pipe assembly connecting the steam and return lines (see picture). Could this be causing any water noise?
Thanks for any help for our c 1900 home.
-wayne

nicholas bonham-carter

Do you have traps on the radiators, and crossover points? If so, they may need new innards.
Keep the pressure down to a few ounces as well, to prevent water from backing up into the boiler.—NBC

EBEBRATT-Ed

Those two pipes look like a loop seal. It is used to drain condensate from you steam line into the condensate return. The loop seal will fill with water to make a seal (loop seal) and as condensate drops into the loop seal it rises in the other pipe and enters the return pipe.

You have to run your pressure low or the steam will blow the water out of the loop seal and cause hammering. That loop seal looks like it's maybe 5'? so you need to keep your pressure under 2psi.

For the loop seal to work the condensate line is usually at a lower elevation than the return, don't know if yours is can't tell from the picture.

Is that where the hammering is coming from?

Jamie Hall

A further comment on that loop seal. I see a drip leg on it. If you can get the cap off of that, check and see that the pipes are free of blockage. In fact, rinse them out.

Ideally the return line would have some slope. It doesn't need much, and it can go either towards the boiler or towards a drip to a wet return. Whether it could be a problem with water hammer, though, depends on where the venting is. If -- as I suspect -- the mains vent into the return with crossover traps, and then are vented to the atmosphere at or near the boiler, then it is possible for there to be some water hammer in that return, but only near the beginning of a heating cycle. Otherwise, I would check everything for slope. The condensate must be able to drain to a wet return somewhere.

EBEBRATT-Ed

@Jamie Hall
had a good idea that I didn't think of. If the hammering is in that location that loop seal could be plugged up. Especially where it only looks like 3/4" pipe

wam525

Thanks guys for the comments. I didn't have the time to get back to this over the past few months. But from what was said, I think the problem is likely the return line slopes. The water hammer is somewhat random, and doesn't occur at this descending loop seal. Most of the day the heat is quiet. But to change the slope of the return line will not be easy, even where they are exposed. So we may just have to live with the noise. We are used to it, but it still can shock guests ;-)

P.S. the steam pressure upper cutoff is 3 lbs, but I will try to see if lowering it helps. That would sure be an easy fix in an ideal world.

Jamie Hall

3 psi is way way too high (you would need 7 feet vertical from the bottom of the seal to the lower of the two pipes). That loop seal we were muttering about will be blown every time the pressure gets close to that, and it will do evil things.

wam525

Thanks, Jamie. I'll drop it incrementally and see if and when the noise abates. Would the differential also need to be lowered?

Jamie Hall

Just make sure that if the differential is subtractive that the cutin pressure -- the cutout minus the differential -- is at least a half pound, unless you have a vapourstat in which case it can be as little as 4 ounces.

Cutout pressure should be less than 2 psi. If you have an additive pressuretrol (such as the kind with a blue-grey box and only one scale visible) that one visible scale is the cutin pressure -- and needs to be set as low as it can safely go (about 0.6 psi) and the inside white dial -- the differential -- should be set to 1

wam525

Thanks, I'll give it a try just as soon as this warm spell ends. The gang doesn't like the heat on when it's so warm ;-)

veteransteamhvac

Loop seal, yes. Although you didn't provide a photo of your boiler, with the loop seal I wonder if you have an equalizer piped on it. I'm going to guess no. Also, it's probable your 2 pipe system radiators do not have return traps. Any steam finding it's way through them into the non-sloped return could cause the occasional far away hammer.

wam525

Good call. There are no equalizer or Hartford Loop pipings. I've appended a pic of the boiler.
I've also included a pic of the "trap" on the radiator outlet. but I don't think this can shut off any steam flow, so the steam getting to the return line might be correct.
The inlet has a Danfoss regulator. Thanks.

Jamie Hall

That's a Broomell return elbow you have there. Ingenious gadget, no moving parts. A dip with a weir (imagine a very small running trap) which is the bump on the bottom, and there is a small hole on the top to let air pass.

This is a vapour system.

To work properly -- if at all -- you must use a vapourstat to control the boiler pressure, set at no more than 7 ounces per square inch cutout pressure. Further, you must control the steam input to the radiators. Hopefully you still have the Broomell control valves on the inlets. If not, problem. You will need to size and install orifices on the inlets to control you steam flow.

wam525

Well, most of the valves on the radiators were replaced with standard faucet style valves, before we moved in. There were only two of the Broomell valves left, and these were not in good shape. I replaced these with the Danfoss thermostatic valve. But on the other radiators we just adjust the orifice till the radiators get properly hot, and then never adjust them (although often kids and guests don't know that) :-)

If the vaporstat is set at 7 oz, what should the differential be? Thanks.
Wayne

Jamie Hall

3 ounces, for a cutin of 4 ounces per square inch.

Jamie Hall

I might add -- those Broomell return elbows have two rather small holes to let air and water through. They have been known to get clogged;, so if a radiator is heating poorly or not at all, it is possible to separate the union and get in there are open up the little holes...

wam525

Thanks. The radiator gets hot, so the steam hole must be open. But I guess if the water bypass is blocked then the water would have to also go through the tiny air hole, and this would surely be an issue. I'll check the hole if the problem persists after I lower the steam pressure to 7 oz.

dopey27177

Good call on the radiator outlet.
The problem here is at the boiler.
It looks like a 3" pipe is feeding a 6" pipe. Setting the steam pressure at the boiler is a no no.
You need to put a pressure gauge on the 6" steam main. Operating the boiler at under one pound of steam may not put the 6-8" of steam pressure needed in the system. When the steam leaves he 3" pipe there will be a pressure drop as the steam enters the 6" main therefore a pressure gauge set on the steam main will allow you to set the boiler pressure to supply the 6-8" you need the system.

Jake