calculating main length for venting

SteamedInWharton

I have four 2" mains that supply my radiators. After reaching the last radiator, they're reduced down to 1 1/4" pipe and run back to the boiler room and dropped to the wet return. When calculating venting (e.g. 1 Gorton #2 per 20ft of 2" pipe) does the 1 1/4" pipe need to be accounted for? E.g. vent 40 ft of 2" pipe and 30 ft of 1 1/4" pipe (straighter path back) or just vent 40 ft of 2" pipe?

KC_Jones

Do you have 1 pipe or 2 pipe system?

SteamedInWharton

My apologies. it is one pipe.

KC_Jones

On one pipe you only need to worry about the pipe up to the last radiator, the rest is dry return and there isn't any need to vent it. So in your case it's (assume all rads take off the 2" pipe) you calculate the 2" pipe only.

SteamedInWharton

OK. Thanks

dennis53

I feel it makes a difference where your vents are located. If your vents are located just after the last radiator take off (end of main) then yes, do not calculate the dry return. But if for whatever reason your vents are located at the end of the dry return, I think you should include the dry return in your calculations. It also helps to insulate whatever pipes are before the vents.

Fred

There is air in the return lines and until steam gets to the end of those returns (if that's where your vents are), the vents are not going to close so that steam can then begin pushing the air out of the radiator runs and subsequently the radiators. If your vents are immediatley after the last radiator run, don't add the returns in. If the vents are at the end of the return, add that piping/air into your calculation as well.

nicholas bonham-carter

A good low-pressure gauge, (0-3 psi.) will show the resistance, (back-pressure) of the air exiting the vents, in a perfect world, there would be enough vents on the system to offer no resistance to the air escaping, just as if there were an open pipe.--NBC

SteamedInWharton

Some good answers here. Yes my vents are at the very ends of the mains before they drop down to the wet return.

I have a low pressure gauge and while there are several compounding issues at the moment (poor skim job and poor near boiler piping) I see an initial pressure build up where the boiler hisses, sucks, and surges about 5 mins after start up but the gauge never rises above 0.5 psi and then it calms down a few minutes later.

Originally I had a Gorton 1 on each of the mains regardless of length.

Right now I have:
short main 1: antler with 2 Gorton #1's
short main 2: single Gorton #1
long main 1: Gorton #2
long main 2: Gorton #2.

My eventual plan is to have a Gorton #2 and a #1 on each of the short mains with each long main getting 2 Gorton #2's and 1 Gorton #1.

This is hampered by the fact that the tapping for each main vent is only 1/4" (which I believe maxes out a Gorton #2). The tappings are in a threaded 1 1/4" plug. I've bought new plugs threaded for 3/4" to do the long mains, but I'm having difficulty removing the existing plugs. I may have to cut them out.