A One-Pipe Steam Mystery

New England SteamWorks

See attached photo

Something very curious going on here and I sure could use some help.

The system will run just beautifully for a day or so. Never gets higher than 8 oz, mostly runs at around 4 to 6 oz. Water line very stable, water clean. All good.

Then for no apparent reason the steam will begin to favor the left main and starve the right.

Once it gets into this starve-the-right-supply-main, -it stays there. Cycle after cycle. Half the building cool. The pressure will now be between 1lb and 1.5lbs, and the water in the gauge glass will be 2-3" lower than when the system is operating normally, though still stable. When the cycle ends, all of the water returns within 4 minutes.

To correct, all one has to do is open a drain on the return and remove a cup of water or so: Steam will instantly beginning flowing again to the right supply main, and within a few minutes the right returns will all come back hot, the building will warm, and all will be well again. Until the next time.

Seems a vacuum is setting up. Why and where? And how can the vacuum remain even during an off cycle and then into the next one?

When in it’s dysfunctional state I have removed all the vents on the right returns leaving only open pipe and this had no effect on coaxing the steam into the right main(s). Steam does move into the right man(s), but very little. It did appear when I had the vents off. It took about 10 minutes, when normally those returns are hot in 3.

There has never been any hammer, everything very quiet.

Pitch and all the piping is good. One must keep in mind that the system works just fine for the most part (until it doesn’t) so the problem is transitory.

I set the Vaporstat to cut out at 1lb yesterday afternoon (It had been at 1.5lbs.) thinking a higher pressure was triggering something. Will see this morning. We are also going to rig some clear hose up the returns and observe the water levels. Also going to plug some of the vents on the left return, even though when operating normally and as currently vented the left main heats slower.

Any other thoughts or ideas?

BobC

I'm no expert but the one thing I see in that picture is you have two returns tied together at about the height of the equalizer. That should be ok but if the water level moved for some reason who knows. The clear water level tubes may reveal something.

Have you tried adding an extra inch of water to the boiler to see if it changes anything?

Bob

Abracadabra

What's the situation with radiator vents? Are they all slow vents? I've seen it where radiators vented quickly would literally suck the steam out of main starving other radiators for steam. Once the steam started condensing, would create a vacuum drawing more steam into them. Granted, this was on a common riser. Just an idea.

Has meter been clocked to ensure you are at correct firing rate and you're getting the steam you think you should be out of it?

New England SteamWorks

Update: Ran fine all last night. This morning we lowered that return wye all the way down (BobC) even though it was a good 5" below the WL. (Several days ago we had added a little more water, no effect). We also set up the clear hose on the returns today. Nothing to see there (yet) as she is still running just fine.

Radiator vents are all VentRite adjustables. Before start up we put them all at 1,2 or 3 based on their radiator size. Gas is good.

Thing is, -it runs beautifully for a day or so. Then not. Open return quick, fine again, all better.

Not sure what to try next if it re-occurs, beyond observing the water in the clear hose. So perhaps I should be asking: What should we try next in this process of elimination?

DetroitSteamHeat

Is there any insulation anywhere on the mains? What is the relation of boiler output to radiator size? What is the average time between cycles?

nicholas bonham-carter

Is there some horizontal pipe in the return, or supply, which somehow can change pitch with pipe expansion, as the system heats up, thereby trapping water? This could be far away.
Is a vacuum registering on the gauge during these times? Are the main vents on that slow side becoming water-logged in the antler?
Maybe removing the main vents temporarily during the problem time would show something.--NBC

New England SteamWorks

DetroitSteamHeat said:

Is there any insulation anywhere on the mains? What is the relation of boiler output to radiator size? What is the average time between cycles?

The mains are all insulated. The near-boiler piping is not (owner is doing) but the insulation for that arrived yesterday.

Boiler 894 / radiators 808

Weather dependent of course, but around 30 minutes between.

New England SteamWorks

nicholas bonham-carter said:

Is there some horizontal pipe in the return, or supply, which somehow can change pitch with pipe expansion, as the system heats up, thereby trapping water? This could be far away.
Is a vacuum registering on the gauge during these times? Are the main vents on that slow side becoming water-logged in the antler?
Maybe removing the main vents temporarily during the problem time would show something.--NBC

I have spent a lot of time looking at the piping and can't find anything on the slow side. And, of course, this problem didn't exist until we showed up. Also, the slow side tees off 8' after leaving the boiler and both sides are effected. Soo in theory if it were a piping issue it would have to be before that tee.

No vacuum registers.

I have completely removed the vent antlers (see initial posting), -no effect.

ChrisJ

have you tried slowing up the venting on the side that steals the steam?

Are the vents on the "working" side opening fully between cycles and letting air back in?

PMJ

Could we possibly see a hand sketch schematic of the mains, returns, and vents on this system?

Also, does the outside temp - that is the level of demand for heat - affect whether or not this conditions occurs?

jimmac

The problem was there before you got there ,no one caught before because of the 47-2 it kind of eased the vacuum.Try adding a check valve backwards into the system and see what it does.Either in the bull of the tee you have added on the water column or pull the pop safety add a 3/4 tee on the nipple from the boiler(tee on the run)install the pop safety back on top of the tee .On the bull of the tee add a nipple and swing check (check valve pointing into the boiler) into the boiler-
You will be able to see what the system is doing at what point in time ,by how the check valve reacts.If you don't follow me in box me.Your minimal investment in material and time might prove a useful tool.

New England SteamWorks

Adding an update for posterity (nothing worse than searching out a problem and finding an old thread that ends without conclusion...).

The problem never reoccurred. Changes made after the last occurrence were to complete the insulation of the near boiler piping, reduce the pressure cut-out from 1.5psi to 1.0psi, and lowering the return wye that was already 5" below the water line to 7" below the waterline.