Check valve

Schvenzlerman

The water in my steam boiler commonly leaks past a swing type check valve (3/4" NIBCO) back into a condensate receiver. When the boiler's low water cut-off senses this, the receiver's pump engages to send the water back into the boiler. The check value is installed correctly, so that's not an issue. I replaced the check valve's swing. Same leaking condition. It might be the check valve's seat, but it looks okay and my thought is to replace the check valve with a different type. A plumbing supply house told me that the solution was a spring type check value. I'd appreciate ideas: what type, manufacturer? Thanks.

nicholas bonham-carter

Leaking check valve

Is the pressure high enough to force water back through the check valve into the condensate tank? Why do you have a condensate tank, when you could have a gravity system?--NBC

Pumpguy

I don't like

spring type check valves because they add to the total pressure the pump has to discharge against. 



I would do a leak-down test on any check valve before I use it.  Low pressure (maybe 5 psi or so)  compressed air with the check valve in a bucket of water will show bubbles if there's leakage.  Simple mouth pressure can also be used if you don't mind doing it. 

Schvenzlerman

Gravity vs. Receiver

Perhaps I should change to gravity. We have a 2-pipe system from around 1946. It operates at 1/2 lb. pressure due to big pipes. When we bought the home, a new boiler had been installed, a Weil McLain LGB-6. The boiler's installation manual indicates the need for a receiver, so the plumber installed a Bell & Gossett receiver but it was grossly undersized. This resulted in the receiver spitting steam and water through its air vent. Basically, the system could not "breath." I had someone install a larger receiver (boiler feeder) as stipulated in the boiler installation manual. What are the requirements for gravity to work?

Jamie Hall

As I read the manual...

for that baby, it says, "Where condensate return is not adequate, a low water cutoff and pump control, condensate receiver, and condensate boiler feed pump should be added" and it gives you a figure.



But the key words are right at the beginning: "where condensate return is not adequate".  It does not say it is required; only if the return is too slow.



So... the question is, is your return too slow?  Do you know?  if it is, have you investigated why it is slow?  It would be much more satisfactory to fix the slow return problem and let gravity drive, if you can.  Which, unless your place is really immense, I expect that you can.



Forgive me, but I think someone mis-read the manual.

Schvenzlerman

"where condensate return is not adequate"

I have never run the boiler without the receiver (boiler feeder), so I cannot say whether or not the condensate return would be too slow without it. I can say, however, that the steam-to-condensate return time is about 13 minutes. I don't know if that info is useful. To address your other point, the home is four stories at just over 10,000 sf. The LGB-6 has input of 650,000 btu and output of 526,000 btu. I guess that I could pipe from the final condensate return point to the boiler for the purpose of by-passing the receiver and see if it works.

Jamie Hall

13 minutes

does seem a bit long, but could I ask how that is measured?  If it's from the time the burners first fire to the first sign of condensate coming back into the receiver, then it may not be.  The real question is how long from when steam really starts to form (the header gets steam hot) to that first condensate return.



You could indeed run the system piped to bypass the condensate receiver, and it would be a good test if you can do it without major complications.  However, when you do, keep an eye on the boiler water level, as that is your real criterion.  If your water level doesn't drop that much, and then holds steady while the boiler is firing, then you should be -- in my opinion -- better off with a straight gravity system.



You might also consider the condition of your wet returns.  Is there any way to flush them out?  They do sometimes get gooped up and slow for that reason.

Schvenzlerman

Clarifying condensate return time

"from when steam really starts to form (the header gets steam hot) to that first condensate return" is approx. 13 minutes. Not sure about flushing out the wet returns. Would have to look at that.

nicholas bonham-carter

13 minutes

That slowness of return may be due to poor main venting. Maybe the steam gets to the radiators very slowly, and then begins generating the bulk of the condensate.--NBC

Schvenzlerman

Slow steam to rads?

I perhaps should have mentioned that virtually all of the home's 36 radiators are convectors (5 basement rads are cast iron).



Two of the three mains are properly vented with correct vent sizing (looks like Christmas trees). The third is not because it would have to be tapped for such purpose.