Single Pipe Steam Issues

dyoung9121

I have an old residential house that has 2 new steam boilers with a single pipe system. The problem is, is there is a condensate return tank in the boiler room with a vent and steam is pouring out of the vent. There are no steam traps, so wouldn’t it be natural for steam to vent in that setup? Also the building has baseboard heat but I cannot find any vents for the baseboards. Any help would be appreciated.

Jamie Hall

Well, it would be natural. It's also not right. If you have a condensate tank (why?) and it's vented, you have to have -- no options -- an F&T trap at the end of the steam main, before any piping which leads to the condensate tank. The next question would be... why do you have a condensate tank at all? And the third question is -- baseboards, like any one pipe steam radiation, must be vented somehow or they simply won't heat much. Do they perhaps have returns? Piped as two pipe? And if so, where do those returns go?

dyoung9121

Okay, I do not know exactly why there is a condensate tank. This was installed by another contractor awhile ago and I am not sure why but I could make several guesses. My first guess would be sized incorrectly. I have to look into the baseboards a little more because we do not know if they have an actual dry return but would that be unusual to have a 2 pipe and 1 pipe hybrid system. We cannot find any traps anywhere

Jamie Hall

Two pipe and one pipe hybrids aren't that common -- but I wouldn't say they were that unusual, either.

And as I say -- no traps, vented condensate tank, steam out the vent. Inevitable.

EBEBRATT-Ed

@dyoung9121

What @Jamie Hall sayed is correct.........unless they put a loop seal which would be a big loop in the return piping dropping to the floor and back up. If you have a loop seal and your steam pressure is too high you might have blown the water out of the the loop seal.

If you have no loop seal ad no traps then something is amiss

dyoung9121

I’m trying to envision a loop seal.....you wouldn’t be able to draw a picture for me?

dyoung9121

Okay, my bad, it doesn’t have a loop seal, just the Hanford loop going into the condensate tank

Jamie Hall

dyoung9121 said:

I’m trying to envision a loop seal.....you wouldn’t be able to draw a picture for me?

Not a picture, but a description? Picture, in your mind's eye, the end of a steam main. Attached to it is a pipe which goes straight down, perhaps all the way to the floor. Then, at the bottom of the pipe is an elbow -- let's say to the left (doesn't matter). Then a short length of horizontal pipe. Then another elbow which turns and points straight up. Then a pipe which goes back up to near the ceiling, and which connects to the dry return.

That is a loop seal. What happens is that condensate gets in there, inevitably, so you have water in the bottom. With the water there, you can't have air -- or steam -- going from one side to the other. Now if the pressure of the air -- or steam -- on one side is greater than the other, pushing down with more force, the water in the other side gets pushed up -- until the weight of the water in that side is exactly the same as the weight of the water plus the pressure in the other side -- the forces are balanced.

This maintains the seal -- air or steam still can't get around. But what happens if the pipe on one side isn't tall enough? The weight of the water on that side can't become enough to balance the pressure of the steam on the other, and the steam pushes the water out of the pipe -- and then is free to come around the bottom and pass from one pipe to the other.

That required balancing height of pipe is known: 28 inches of height will balance 1 psi of pressure (water, of course, here). So if we assume a typical basement, and the height of the loop seal is seven feet, the most the seal can balance is 3 psi. Anything over that and... poof.

luketheplumber

Looks something like this.

dyoung9121

Thank you, we definitely do not have a loop seal on that system, but it is nice to know for future reference