Dripping vent on Watts check valve

04090

4 GPH Burnham V7 steam system circa 1997, unremarkable history and no recent modifications.



A Watts 9DM check valve (has a steady drip from what's labeled the vent. It's mounted on a pipe leading to a condensate tank, and there's a pressure reducing valve just after the check valve and a typical water valve just before it.



I can't see the model of the reducing valve because of how it's positioned, but it's the kind that has a lever that swings across the top. As I recall it having been explained to me years ago, when the lever is positioned in the center (across the top of the valve) full water pressure is allowed to pass and when it's near the base of the unit it's in pressure reducing mode. I add this only because it seems to swing around freely - ie without pressure or seemingly any change in function - and I'm not sure it's doing what it's designed to, but then again I've never had occasion to flibble the lever.



My first thought was simply to replace both parts as I don't understand how they relate to each other. I see a cause of leaking could be imbalanced pressure on either side of the check valve.



How should I proceed?



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(Added: Searched around online and the pressure reducing valve looks like a Bell & Gosset FB-38)

Jean-David Beyer

The leaking valve is an backflow preventing valve.

Bear in mind that I am not a professional. But I do have a (defective) anti backflow valve generously donated by someone on this Wall. I have taken it apart and see how it works. Inside it are two spring check valves in series, with the vent between them. In normal operation, those check valves would be open and the vent would be closed; no water would come from the vent. These valves could wear out, probably because the seats of the check valves or the vent valve deteriorate, or some grit got in them. So one possibility is that that is what happened and you should just replace the valve. If it has been leaking for a while, another possibility is a build-up of mineral deposits. I looked the price up on the web and it is not horribly expensive, but it is way more than a ball valve.



It seems that a backflow preventer and a pressure reducing valve are often sold together as a unit, which could be a convenience. In my situation, there would not be room, and mine are installed a couple of feet apart. If these are both old, you might have them both replaced on a single service call. But otherwise, and if the valve is defective, just replace the defective one.



But if the valve is OK, then the vent opens when the supply water pressure is way too low. The valve is trying to ensure that the water from the delivery port never gets back into the supply, even if the input check valve leaks. (Getting boiler water, that might have anti-freeze or other boiler treatment chemistry, or even harmful bacteria, must be prevented from getitng into the supply because you or your neighbors might be drinking or cooking with it.) Another reason that the vent valve could open is if the supply pressure is less than the delivery pressure and the delivery check valve leaks. To contaminate your supply water, you would need three failures of the backflow preventer at the same time. Both checkvalves would have to leak and the vent would have to be stuck closed. Very unlikely. But if it is leaking, you do want to get it investigated and replaced if necessary.



So before replacing the  valve, you might look at your supply pressure and your boiler pressure. Your boiler pressure might be too high because of a defective expansion tank. If you are not a professional, I suggest you get one.

04090

response

Just for clarification, there is no expansion tank on this steam system. The valve leads to a well vented condensate tank.



Water supply pressure is strong.



I see there's a rebuild kit available for the backflow preventer (RK 9DM2 T) but don't know if that valve or the pressure regulator is the problem. Or if it's worthwhile for me to try rebuilding it or just replacing it or both devices.



Am tempted to drain some water form the condensate pump, flip the lever on the pressure reducer to street pressure and let some new water into the system just to flush any crud that might be in the valve. Might that be worth a try?



I'm baffled on what to do here as I understand what these devices do but not how they work.

Jean-David Beyer

I forgot you said it was a steam system.

I never heard of there being an expansion tank on a steam system.



I do not know much about steam systems, so I do not understand why you would pipe potable water to a condensate tank, or why you would want the condensate tank under pressure. On the other hand, if you do need to supply water to the tank, it is certainly appropriate to have a backflow preventer in there. But why is that tank under pressure at all? And why so high as to use a pressure reducing valve that is probably set around 12 to 15 psi? That is pretty high for a steam system. As people are fond of pointing out, the Empire State Building uses only about 3 psi. If that tank is running pressures greater than the domestic water pressure, typically around 40 psi, I would be really worried, and not just about the backflow preventer. Is your pressure control device set wrong, or defective? And why is the pressure relief valve not opening?



There is a lot here that I do not understand. I hope the pros do.

04090

response

The condensate tank is like a big bucket on the floor next to the boiler that collects the return water from the steam pipes and holds it until it's called for by the boiler. There is no pressure within the tank proper. But the tank also doubles as the device that calls for street water to be added to the system as needed, and the pressure reducing valve is in line just before a toilet tank like float mechanism within the tank that maintains a preset water level. I think that muddled description covers it for you, JBD. Thanks for your comments.



I found Watts brand replacements for both parts at the local orange big box store, but before I install them would really like to know if there's anything I can do just to repair what's there.

04090

conclusion

I replaced the pressure and backflow preventor. Big orange home store had both, and it was a lot easier to remove the old and install new parts than I thought.



Will assume the problem was a clogged inlet screen on the backflow preventor, and it's possible that cleaning that would have solved the problem. But since I don't know any better and needed to fix the leak from it's vent, I just replaced everything and all's well.