Condensate lines and ceiling height. best practice.

Grallert

Hi everyone. We are having some renovations done here at school which require raising the condensate lines of our two pipe gravity low pressure system system. The pipe fitters are insisting on raising the condensate lines above the steam pipes and the F&Ts and installing swing checks. This seems like an accident or issue waiting to happen. Seems counter intuitive to me. We operate at about 1 to 1.5 pounds of pressure. I guess that's enough to push the condensate along but... Should I not worry? Thank you for any advice or reassurance.
M

Jamie Hall

Me, I'd worry. A lot. As I recall, you have regular thermostatic traps on all your radiation (did you ever do that experiment to test them?). Therefore... you really don't have any pressure in the dry returns. On the other hand, the dry returns don't actually have to be any lower than the steam lines either (I don't recall -- no crossover traps).

Further, you really don't need or want the F&Ts -- that would be double trapping and can lead to some interesting problems.

And you certainly don't need check valves.

Grallert

Hi Jamie, How have you been? Thanks for the reply.I never did get to recruit the students for that experiment as the professor moved on shortly after your visit. I have however been able to service some of those radiators and traps. Now all of those connected radiators are functioning. There are a couple that are disconnected and I'm not sure why. That's for another day I suppose.
The area that is having work is new, newish 1956 HA!! Wall mounted convectors with traps and thermostatic valves. The F&Ts are on the mains below. I worry about the amount of opening and closing the valves do maybe causing a pressure drop and or vacuum on the inlet side of those F&Ts, as we are at a pretty low pressure and I'd like to get it even lower. Do you think the swing checks are simply a waste of money or could they cause any real issues?

Pumpguy

We have all been taught that all fluids, liquids or gasses, flow from high pressure to low pressure, always.

It seems to me that with your existing low supply pressure, the only way to get the necessary pressure differential to get that condensate to go uphill is to have a lower pressure in the return line. Depending on the amount of actual lift, that will probably need to be a pressure lower than atmosphere; a vacuum.

If that's not practical, then condensate pump(s) acting as mechanical lifts are a common solution to this type of problem.

The attached file shows the piping arrangement.

Jamie Hall

If your plumbing chaps insist on having the dry returns high -- and there are no crossovers (I don't remember any) -- they can be above the steam mains, just so long as they are below the trap outlets on the radiation.

Not the way it would usually be done, but it can work -- and sometimes it's easier to not fight city hall..

The F&Ts on the mains may be serving as the mains venting. Do they also route the mains condensate into the returns? If so there should be enough pressure in the mains to boost the condensate up -- 1 pound will give you 28 inches of lift -- but I would be inclined to put loop trap down far enough from the trap to prevent steam from blowing through to the return. I don't think a check valve on them would be necessary. I could be wrong...

I'm fine -- only a year older. Sorry about that experiment -- it sounded like fun and a good learning thing, too. Things happen...

Grallert

thanks again for the replies gentlemen. the F&Ts are venting and draining condensate from the mains to the returns no cross overs other than the F&Ts. I'll have a look first AM to see how far they got. Boy ya learn something new every day, if you're lucky.

Grallert

Well these are the F&Ts newly reinstalled.Sure does add height to the ceiling.
It's fun to learn something new after so many years.
That you guys for sharing your knowledge. It's never boring here at Miss Hall's School.