Main steam vent

mmaherhealion

I have been advised that I need a main steam vent on my gas boiler. The main runs approximately 60" from boiler to an elbow that runs approx 10" and branches up to first floor. Would the vent be installed on the pipe before the elbow? Note: The technician that came explained he doesn't do this type of work but said the reason my first floor radiator valve is shooting hot water (new valve/radiator properly pitched) is because I have no main steam vent.

Jamie Hall

Well... you should have a main vent there. Thought 5 feet isn't a whole lot o main. Still wouldn't hurt.

But... that's unlikely to cure the radiator vent of "shooting hot water". You say that vent was replaced? Why?

The most common problems are venting the radiator much too fast, or water being trapped somewhere in the line leading to the radiator and getting shot into the radiator. I'd check the slope o that 5 foot main and o the branch...

echosair

Can anyone explain to me why water would spit out of the main vents on the piping system that's about 30 and 50 feet from the boiler. It seems the low water cut-off would turn off the gas and inject more water into the boiler. You would think after a few cycles the condensate would come back to the boiler. We replaced the motor on the condensate pump due to failure. Once the system was started up we noticed the water spitting out of two main steam vents. We thought since the original motor failed that the condensate was still in the buildings piping. The piping consist of some underground returns but only where it needs to get to the other side of a archway. Is it possible these could be plugged and causing a rise in water. The main vents are about 7 to 8 feet higher than the boiler. Or is it possible that somewhere in the return there is leaking in the underground piping and if so how would I locate the leak?

Jamie Hall

Are those pipes insulated? Insulated or no -- but particularly if they are not insulated -- a surprising amount of condensation occurs in horizontal main. It's nor likely that that is what you are seeing, particularly if the vent is very near the end of the main.

This happens even if the main is counterflow, but the potential is much greater with parallel flow. And MUCH greater if the pipes aren't insulated.

echosair

The low water cut-off continues to shut down the firing and does a slow fill. This is causing short cycling and it keeps introducing new water into the boiler. I tried shutting off the water feed for 24 hours just to see if the spitting of water through the vents would stop. It Did. I noticed that when the boiler was off cycle the water would slowly rise to engage the firing once again. I Did turn the water back on to the auto feed after 24 hours by the way. Any thoughts?

echosair

The pipes are not insulated outside the boiler room. Coming out of the boiler room it heats a large fellowship hall on the same level while it also feed a large sanctuary above. The radiators are fin on steel 2 inch piping.

Jamie Hall

Well, at least the low water cutoff is doing what it's supposed to do...

If higher water levels in the boiler are indeed part of the reason there is water in the mains making the vents spit, the near boiler piping may not be as it should be. Can you get some pictures o that and post them?

Get those pipes insulated.

You also have a slow return problem. How does condensate get back to the boiler in this system?

neilc

what boiler pressure are you seeing when the vents are spitting ?
how dirty is the water in the sight glass ?
does that water level bounce, a lot, when firing ?
a picture of the sightglass, Ptrol, and general boiler could help.

echosair

After changing all the F+T traps and a bunch of thermostatic traps we thought we had it licked. This week we stopped in and found the same situation of the water spitting through the main steam vents. The boiler short cycles as it runs for a minute or less then shuts down for 2 minutes. After short cycling the so many times the motor on the condensate pump took a hit. The first motor was found dead when we first entered the project. This would be the second motor that took a hit. The water in the site glass fluctuates
a 1/2 inch up and down then gradually



goes to the bottom and the pressure shuts down at 4 psi. The condensate return pump ties into the return piping with a 1" line and looks like a hartford loop, but its not. Not sure what to do next. Any thoughts anyone?

JUGHNE

For the pump problem, is there a working check valve in the return line feeding the boiler?

echosair

Yes this is one of three vents on the same level and they are approximately 5 feet above the condensate line. The water level of the boiler is about 35" above the finished floor (AFF). The condensate might be around 37" AFF.

echosair

Yes there is a 1" working check valve in the line feeding the boiler from the pump. However, the return line of 2" also ties into the return of the boiler without a check valve.

neilc

Do you need that 4 psi pressure for airhandlers? or what?
seems pressure is pushing water out of the boiler, and up to places it doesn't want to be,
( dial it down to <2 )