How do I tell if my boiler pressure reducing valve is bad? I can't seem to purge my loops

Jells

I added a new zone to my boiler manifolds today, and when I tried to purge the air from the loops I can't get enough pressure from the reducer, flipping up the lever seems to have no effect on the flow. Is there a trick to fixing/clearing these, or do I just get a new one?

It's one of these, a Bell & Gosset FB-38


EDIT: found the data sheet on this and it mentions cleaning the strainer screen. I'm going to wait till after the wife takes her morning shower before I risk taking down the heating system if I have a problem! Noisy baseboard is better than that.

rick in Alaska

You can try cleaning the screen, but in my experience, when they get plugged up, they don't clean up well and usually leak. Yours does have a brass body instead of cast iron, so you might make it work. Most likely you will need to replace it.
Rick

Jamie Hall

To which I would add that it is a very rare situation where a pressure reducing valve such as that will pass anywhere near enough flow to actually purge a loop of air. You need to really get that water moving.

Jells

Jamie Hall said:

To which I would add that it is a very rare situation where a pressure reducing valve such as that will pass anywhere near enough flow to actually purge a loop of air. You need to really get that water moving.

I've never heard of another method except vents on the rads. It's always seemed to work for me. Do tell of another method? Hook up a hose from a direct bib to one of the drain bibs to get line pressure? Gotta be careful with that, I've had old systems leak from a bad pressure valve that was not reducing!

Jamie Hall

Indeed. Hook up a hose directly and let her rip. Just don't close the valve on the other end, and you'll not build much pressure in the pipes. If you are concerned about old pipes, just close the valve on the hose down enough to keep the flow down to say 3 or 4 gpm.

HVACNUT

Is the manual valve before the PRV open?
I wouldn't open it to clean without a new gasket.

Jells

So I replaced the PRV, and tried Jamie's idea. I think it destroyed the valve! When the boiler was running this valve preset to 13psi shot the pressure up over 60, which is how I discovered my safety relief valve was bad. This just keeps getting better. I had to unscrew the setting screw on the PRV all the way to get it under 20psi, and it still seems erratic.

Or is it possible I overheated it when sweating the joint 8" away? I had to heat it pretty long because there was some water in there. If I have to redo this I'm adding a union, don't know why these valves don't come with them to begin with like tempering valves.

HVACNUT

Taco and Watts and others offer them with unions.

Jamie Hall

I don't see how it could have destroyed the valve -- if you did it right. There should have been no flow through the pressure reducing valve at all, and the pressure in the whole system should never have gone over perhaps 10 pounds.

hot_rod

when pungent purging, if possible isolate all the zones or loops except for the one you are purging 

In fast fill you should get 5 gpm or more