main vent question for two pipe system

Brian_74

On a two pipe vapor system, should both the supply and the return mains be well vented, or is it only the supply main vent that needs multiple vents (and the return can have just one)?

Rod

Two Pipe System Venting

Hi Brian- As I remember you didn't have cross over trap, the end of your steam main dropped into the wet return. (?)  In this instance, of course, the steam main needs to be well vented. 

On a two pipe system I think the return side also needs to be vented well too. To quote Gerry Gill's famous saying, " Before a steam trap is a steam trap, it's an air vent!"  So on start up all the traps are passing air into the return main and this air has needs to be released from the return. If you think about it, if all the traps are properly working, you could probably get away with a vertical open pipe for a vent but we need a steam vent on the end of the vertical pipe just as a precaution so we don't get steam all over the basement in the event that a trap sticks open.  It would then seem to me that you would need to have this return vent of a fairly large capacity other wise the initial air release from the return would be restricted which would slow the passage of steam into the radiators.

It might be worth trying an open vent pipe on the return with a temporary ball valve and time the system just how much difference it makes having full capacity venting vs a regular single vent. The needed venting capacity depends a lot on just how much the radiators vent in parallel or sequentially or a mixture of the two.

Just a thought .

- Rod

Brian_74

On the right track, then

Thanks, Rod. You're right about my system. When I bought the house, there was a Hoffman 75-A (I think--it's NLA and was meant for coal-fired systems) on each main, just before they dropped into the wet return. The massive venting idea made sense to me, and I put two Hoffman's on the supply main and three on the return main. (I had wanted to try Gorton's but at the time they were having quality control issues. Thank goodness PexSupply was great about the returns). But then a recent thread made me think I had misunderstood about the return mains. I'm glad you straightened me out!



I'll have to try the ball valve idea after the holidays. That's a clever idea.



Thanks again!