Damaging thermostatic steam traps

Robstorms

New user here and pleased to be able to learn from the experts! I have heard authorities say that a stuck open steam trap on a radiator can damage good traps down the line. What is the mechanism that can cause this damage? I think I understand that steam can flow backwards into a good trap, and I would think the high temp would cause it to close but I don't get the damage. Thanks! Rob

mattmia2

the shock from the sudden pressure change from the water hammer from the steam in the returns that got past the bad trap hitting the water in the returns and collapsing.

Jamie Hall

It may damage them, but that is secondary to shutting down steam flow to the other radiators -- making them heat poorly, if at all.

There are, however, lots of ways to damage thermostatic traps. As @mattmia2 says, any water hammer at the trap is lethal. There is a rather delicate bellows in there which does not take kindly to overpressure. Therefore, you also have to watch general overpressure -- one of several reasons why 1.5 to 2 psi is regarded as the maximum differential pressure across the trap (before someone yells -- yes, I know they are rated at 3 psi working. It is not, generally, good practice to run a device right at its working limits all the time).

pedmec

And this will be pronounced when you are using thermostatic radiator valves to control each radiator. With a closed radiator valve and a close thermostatic trap you are going to form a vacuum in the radiator as the steam condenses. As soon as the thermostatic trap opens up, everything will head that way and that's when all hell breaks loose. Thermostatic radiator valves have built in vacuum breakers but they fail like everything else.

Robstorms

Thanks so much for the answers! If I may follow up, easiest way to test thermostatic radiator traps for function? I have a thermal camera and wondered if I could see proper ( or improper operation using that. Thanks! Rob in Rochester, NY

Jamie Hall

Thermal camera or IR thermometer -- you want to see the outlet of the trap at least 5 degrees cooler than the inlet when the radiator is hot all the way across. But -- doesn't have to be more than that.

Robstorms

i wonder if anyone knows of a real steam expert within a resonable service call to Rochester New York? ( 2 pipe system, large old 4 apartment house, one boiler). Looking for someone great at troubleshooting/diagnosis. Thanks !!

Steamhead

@Robstorms , you might start here:

https://heatinghelp.com/find-a-contractor/state/NY

Robstorms

Thanks!!

Jamie Hall

I can't think of anyone in that part of New York -- I think we've had trouble finding someone before. You may need to get a copy of The Lost Art of Steam Heating -- if you don't have one -- and make yourself your own expert.

ariccio

Robstorms said:

Thanks so much for the answers! If I may follow up, easiest way to test thermostatic radiator traps for function?

Try a mechanic's stethoscope pressed on the trap! It's pretty neat, you can hear it purging every few seconds if it's working correctly.