Steam coil damage

Steve Bukosky

I've got a copper tube and aluminum fin steam coil that has splits in some of the tubes that are at the top of the tube and run with the tubing. I suspect that I have trap trouble as upon the steam valve opening, the condensate return heated before the supply. Or, might this be a problem caused by other traps in the return admitting steam and with the valve open, allowing the steam to back up before the trap closes? If so, would this cause condensate to build in the coil and eventually hammer such that the cracks develop? The steam source is from the electric utility and I have no idea what the pressure is.

The picture shows the supply which is the large elbo on the right of the photo. The return is pretty much centered. Coil is off to the right and you can see the side of the air handler. I have a Powerpoint with more pictures and details but is over 2 megs large. If you have high speed and are interested, drop me a line at sbukosky@hotmail.com

Tony Conner

Does This Coil...

...heat outside make-up air through a temperature control valve? Is the rad trap against the wall just a vent, or is it the trap for the coil? (Maybe a trap for something else?) If the condensate line is the horizontal pipe (looks like there's a coupling with a bushing in it, just ahead of a check valve) with the check valve in it, where's the trap located?

I used to work for a steam utility, and I've been in a lot of old brick-walled basements that look just like this one.

Steamhead

More things to check

You have to know what pressure you're running. It is possible for condensate to flash to steam if it moves from a high-pressure zone to a low-pressure zone. This will look exactly like a trap problem.

Also, how does the air get out of this system? Does it move with the condensate to the sewer, or is there a vent on the coil?

Is there enough height for the water to drain thru the trap by gravity? You need at least a foot, sometimes more.

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Steve Bukosky

The trap against the wall...

...is not part of this circuit. The horizontal pipe in the center contains what I believe is a horizontal trap and then a shutoff valve which closest to the vertical pipe. I was concerned about the pressure, thinking that the supply from the utility, which is perhaps a mile away, would be fairly high pressure. To the best of my knowledge, there is no make-up air here, though that is something I'm going to look in to.

Steve Bukosky

One more thing to check...

I was concerned about the height of the draining also. There is no air vent on the coil so it would appear to be forced to travel back through the steam valve into the supply. Or would this not happen and the air be forced down along with the condensate?

Right now I'm thinking we need an air vent and more height before reaching the trap.

Steamhead

A steam trap

will pass air and water, but not steam. So if there's no vent on the coil, the air goes out thru the trap with the condensate.

Water can also be held up in a coil if the steam valve closes and the trap is already shut, creating vacuum. A vacuum breaker is the cure for this.

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Steve Bukosky

Good point. Should that happen, could that cause hammering enough to split the copper tube?

Steamhead

It could

and the water held up in the coil could also freeze.

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Steve Bukosky

How much vertical distance?

For the sake of the discussion, say I have a Hoffman Series 650 thermosidsc trap, which it doesn't have to my knowledge. How much vertical distance should be between it and the coil outlet? The Hoffman paperwork doesn't specify that.

Steamhead

Depends on the available pressure

Which can be as low as zero if there's a motorized valve in the steam line to the coil. If this valve is closed, the only force available to move the condensate thru the trap is gravity. And even that won't be enough if there's a vacuum inside the coil.

I don't have in in front of me now but I'm pretty sure 12 inches will give you a bit more than 1/3 PSI of force, based on the "B" dimension of 30 inches per pound. The more height, the better. If the return is well below the coil, and the trap is right at the coil outlet, it might not be a bad idea to move the trap down closer to the return.

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