Noisy radiator vent -- but not hissing

michael_15

I recently put in a Hoffman 1A (oh boy!) on my largest radiator. Shortly afterwards, I heard some banging and thought "Oh no! Water hammer!"

However, it wasn't. After the boiler cuts out (it's set to around 1.5 psi cut-out) and the system depressurizes, the air goes back into the radiator in spurts. There's a loud hiss as it sucks in air, then "clank!" and it shuts close, presumably due to some steam reaching the vicinity. Then, around 10 seconds latter, a loud hiss followed by another clank.

Is this normal? Does this mean that my cut-out pressure is too high (and I need a better calibrated pressuretrol)? Do I have a defective air vent? Is the air vent (set on the fasting venting) too small? The radiator is a 50 sq ft EDR thin-tube, which I believe means it only has 0.44 cubic feet of air in it.

The system otherwise behaves quite well -- no water hammer, no vent hissing when the boiler is running, insulated pipes, and so forth. I probably make fairly wet steam (header too low and too small), but I don't see how that would matter for this issue.

Thanks,

-Michael

jeff_51

one pipe or two?

michael_15

one pipe

One pipe.