Condensate pump or vacuum pump

Dan M_6

The EDR of the boiler is 7880 Sq ft of steam. The main return line to the pump is about 3" diameter. The system has one shell in tube hx for a hot water loop and the rest is cast iron radiators controled by txv's. I will double check the return lines in other parts of the bldg for diameter next time I am up there. Thanks

Dan M_6

condensate or vacuum pump

I have a job i was looking at, that has a vacuum pump that is in disrepair(ITT Domestic VLR). It leaks and spits water out its vent when the pumps run. Obviously something needs to be done.
The system has been running on float only for several years but still creates some vacuum when running. There seems to be no condensate return issues other than the pump dumping condensate down the drain.
My Question is if i can repace the unit with a condensate only pump? I have no idea if the system was designed for vacuum or if someone got a bright idea at one time to put it in. I had left a vent on the condensate line open and letting them run the system w/out any vacuum to see if there is any issues. Just want to double check. I bet they are loosing 80% of thier condensate from this thing.

Brad White_191

Ouch...80% dumped condensate?

If you are making and holding at least some vacuum, you most likely have a vacuum system especially if it is a commercial application.

Things to look for which would disqualify the "originally vacuum" assumption are vacuum breakers at air handling unit coils and heat exchangers.

Another thing to look for to qualify that it is an original vacuum system are the return pipes. On vacuum systems these tend to be much smaller.

"Rule of thumb" or ballpark check figure is that a normal low pressure gravity return pipe size would be half the size of the supply pipe feeding it.

A 2" steam would have a 1" condensate associated with it. In a vacuum system this well might be 1/2" or 3/4".

I am working on a 1963 designed vacuum system. It has 5" risers and 1-1/4" returns. If gravity, I would expect to see 2" or 2-1/2" returns.

I am suggesting by all of this that you have to know. If you go to gravity return and the return piping was sized for vacuum, they will be well under-sized. That would force you into more "pushing" (increasing pressure), rather than "pulling". I want to save you from that regret.

Brad White_191

Take good notes

and think of how you would design the system if you were doing it as a new system. Not just the main but returns in general throughout. That is what I would do.

If you are comfortable with the sizes as gravity returns, what could I possibly add?

Besides, remember Newton's Fourth Law: Gravity Wins.

Dan M_6

I will evaluate the rest to make sure

Thanks, When I get up there I will look everything over. Your rule of thumb was helpful. Just didnt think of it till u mentioned it and then I remember the size of the returns with vacuum in other bldgs and there is a notable difference. I have a vent valve open now so there is no way the system will hold vacuum. told them to call me if they have any problems. Thanks again for your help.

tim smith

I bet the main problem with this system is they put a new boiler

in sometime in the last 20 yrs and it does not have the capacity, water content wise to handle all the returning condensate and therefore dumps it. Probably need and condensate feed tank where the vac pump pumps to feed tank and boiler level control pumps from the feed tank. That is what I usually find on the retrofit boilers and also what I add when doing replacements.