main air valve cycles open and closed, is that normal? Chasing a water leak

bkc

I'm looking after my church steam system (occupied only on Sundays). It has a Weil-McLain LGB-8 boiler (910 MBH, 22 HP)

This is in a old building with a two-pipe system that I suspect was an upgrade from a one-pipe system, possibly upgraded in the 1950s. The boiler is about 4 years old.

The system has 3 condensate return pumps and a main condensate pump that I converted to a feed pump last year. I also installed a water meter to see how much make-up water we're using.

I noticed when the boiler was new that the blow-down water was pretty black. As the years have gone by the water changed color, it became browner, then more clear, and now its pretty much clear on every blow-down.

Make-up water consumption has steadily increased. Last fall it was about 1.5 gallons a day. Now its about 3.5 gallons a day.

During the summer I flooded the boiler and left it filled to the top for 2 weeks. The water level didn't drop more than an 1/8" inch inside the pressure cut-off tee. Based on this I don't think the boiler is leaking.

I have replaced a smaller air vent that I felt wasn't closing, and today I rebuilt two F/T traps that I suspected where blowing steam and overheating the downstream condensate pump. Though based on observations after system startup, I think that repair may not have made a difference. (there are two other F/T traps feeding the same pump, I've turned them off to see what impact that has tomorrow).

Anyway, at the end of one of the main lines (about 100 ft long, 5 to 4" diam), there's a type 75 air vent. The vent is installed about 8 inches above the main line and the main line and vent 'riser' are both well insulated. This main line is on an automatic valve.

After I restarted the boiler, I set the thermostat for the sanctuary to 75 so that the line would be under pressure for at least 30 minutes.

I noticed (well after the pipes were all hot) that the air vent opens for about 3 minutes, then closes for 50 seconds, then opens for 3 minutes, closes for 50 seconds, etc.

I suppose its normal to cycle somewhat, but staying open for 3 minutes seems a bit long.

I don't think this vent could account for all or much of the lost water, but every bit adds up I suppose. The room with the vent does not feel humid.

Does this cycling seem normal for this type of vent?

The operating pressure of the boiler is currently about 0.5 lbs (cut-in) to 2.5 lbs (cut out) but it coasts up to 3 lbs.

The boiler had been operating at 2 lbs (cut in) to 5 lbs (cut out), but a few of years ago I turned down the pressure-trol as much as possible.

All the other condensate pump tanks seem relatively cool (not blowing steam) other than the one at the end of the main line where 4 different F/T traps feed into it, plus two radiators (I replaced one of the two radiator traps last year).

I'm struggling to figure out where all the water is going. Anyway, should this air vent be replaced?

Thanks

JUGHNE

A mirror held at the vent might show steam at the vent.

You could check the pump vents the same way.

Jamie Hall

No that is not normal behaviour for a main steam vent. I'm wondering if somewhere in that line there is a low spot of sag which is holding condensate -- that would do it.

That water use rate is, as you know, excessive. Keep looking...

bkc

@Jamie Hall Thanks for the suggestion to look for a low spot. I'll try to get above the suspended ceiling and look for a broken strap hanger or something else amiss.

I think there hasn't been any maintenance done on this system in more than 20 years.

Today I checked the condensate pump/tank downstream from the two F/T traps I rebuilt yesterday. Yesterday I had also turned off two other lines whose F/T traps feed into this same tank.

Today the tank temperature appears to be around 140F, which is a big improvement over the 200+ I have been seeing. So maybe the rebuilt F/T traps have made a difference, or maybe the temperature drop is just due to reduced flow. I'll keep investigating.