Wet Radiator air vent a sign of failure?

cubicacres

Our tennant complained about the heat in his bedroom in our single-pipe steam radiator building. We noticed the vari-vent we had on the radiator at level 1 was full of water and replaced it with another vent in the upside-down position for now to cool off the room since it's much hotter than the other bedroom. We suspect it failed in the open position, allowing the room to rise to 80F this morning-the other room is 70F.
Is water in the radiator air vent a sign of the vent's failure & suggest replacement is needed? Other times we saw other radiator air vents blowing steam and replaced it, so we're wondering when vents go bad or can be salvaged with a cleaning, and how you can tell.
We added shut-offs just before the radiator air vents in a few other units that got too hot on the 2nd floor rooms that worked better than using the radiator shut-off valve at the floor (the floor valve one is broken anyway, and we planned on replacing it in the summer when the boiler isn't running).

Hap_Hazzard

First, you're absolutely right that turning off the air vent is the best way to shut off a radiator. We often recommend flipping vents upside-down to turn them off, but this only works with float vents, and only as a temporary measure.

If a vent goes bad, it fails to close when the steam reaches it and allows steam to escape. This steam may condense on and around the vent, but a larger amount of water is usually a sign of something else.

The presence of excess water in a steam radiator means the condensate is not draining from the radiator as fast as it forms. In a one-pipe system, the water has to drain through the valve while steam is still rushing in. The size and shape of the valve and piping is enough to allow this, but there are a number of things that can interfere with it.

The most common cause is incorrect pitch. One-pipe radiators need to slant slightly towards the supply end to allow water to drain at a rate that can overcome the force of the steam rushing in. Several things can happen that can change the radiator's pitch over time. Floors can settle and shift over time, affecting the pitch of the radiator and even the supply piping. The feet of the radiator tend to wear into the floor as the radiator contracts and expands from many cycles of heating and cooling, and the wearing is usually most severe at the vent end. This can usually be remedied by placing shims under the radiator's feet to restore the correct pitch, but if the supply piping is affected it may be necessary to shim both ends.

You mention that the radiator valve was not working. This raises another possibility. Sometimes the valve disk breaks loose from the stem and lies in the bottom of the globe. While the valve can't be closed tightly, it isn't fully open either. You can sometimes get an inkling that this has happened by working the handwheel up and down a few times, but you can't really be sure without disconnecting the union, moving the radiator out of the way and inspecting the valve.

Jamie Hall

I might add to @Hap_Hazzard 's excellent comment -- using the radiator inlet valve to turn off a radiator is not a good idea. They rarely shut off steam tight, but when partially closed they allow the steam to get in -- and condense -- but they don't allow the condensate to get back out. Leading to spitting vents, sometimes banging, and other forms of undesirable merriment.

Leave the radiator valves open on a one pipe steam system and control the heat with the vents.

nicholas bonham-carter

You can always look into the valve by unscrewing the bonnet, which is easier than undoing the union nut on the spud, and moving the rad out of the way.—NBC

Hap_Hazzard

I don't agree. I've had a really hard time unscrewing bonnets. I guess it depends on how old the valve is.

cubicacres

Thanks-we'll check the pitch from last year-could alos be clogged inlet valve with broken pieces inside it. We've had good luck adding shut-off valves between the air vent & radiator for tennants to use rather than the inlet valves at the floor we haven't replaced yet (some look 100 years old in our 1900 building & may have never been updated).

This specific one seems ok now that we added the brass 1/8in shut off with ball valve between the air vent & radiator.

Any thoughts on staying with the shut off like this for individual radiators, or trying adjustable vari-vents (they seemed to fail more often for us), or using a Thermostatic valve/vent for our single-pipe steam?

ethicalpaul

I really like those little valves and they are far easier and foolproof than radiator valves. Keep those and remove the handles on the big ones, that’s my vote