Single Pipe Steam Issues

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?

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.

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.