steam, heat exchager, air vent

neilc

two diferent systems,
the tank is the old two pipe, steam rads,..
the HX is above newer boiler, trap gravity returns to boiler, no tank, no atmos vent

neilc

steam boiler supplies through control valve, to heat exchanger for hydronic system, there is a vacuum breaker off exchanger, then to trap, gravity drops to return .

somewhere here I need an air vent as we have to manually vent air at startup or when demand backs off on warming days


you may ask why heat exch.? this is a school basement with a older steam sys, this boiler could backup the old boiler as there is common piping w/isolation valves on the supply side,would have to quick up the return line. the Hydronic supplies newer hydronic sections of building

now back to my vent question, would this go before the trap or after?
the old sys is trapped, returns to a condisate tank, which is openly to atmosphere vented,
the trap is a float type with air vent
wouldn't the venting want to be after the trap, either to atmosphere like old sys or through air vent?

Unknown

Why is the trap not venting it to the tank's vent?

Do you have a low spot in the return that traps water? Does the thermostat in the trap open? Do you have steam in the return holding it shut? Is the steam pressure high enough to make flash steam from the trap, which would shut the thermostat in the trap?

The trap is supposed to vent it.

Noel

Unknown

Then you're right. Right after the trap outlet, above the "B" dimension.

Noel

neilc

Ah, the B dimension, you gonna make me go look that up arn't you? or could I figure something about the water level, I breifly perused the manual today, but didn't see vent, let alone look for B dim, will have to look for mech print

Unknown

Nope

28 inches above the water line for every PSI of boiler pressure. Put a fat vent up there. The water will climb the returns from back pressure into the vented line. I once used the alternate outlet pluged port on the F&T trap itself, because I couldn't get into the piping.

Noel

Steamhead

Neil, you probably won't find the \"B\" dimension

in their literature, but you WILL find it in Dan's book "The Lost Art of Steam Heating", available on the Books and More page of this site. Also the "A" dimension, which is just as important.

If that heat exchanger runs on just a couple of pounds, a standard main vent will work fine. If not, you need a vent designed for the system's pressure (which may be too high, another topic in Lost Art). But I wonder why the F&T trap won't vent it.

Follow the pipe from the F&T to the condensate tank. That line should pitch down all the way to the tank, and enter the tank above the water level. If it doesn't, that's why the air won't vent. Then you need to install the vent as Noel says.

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