1-pipe steam air vent question

ross moore

OK, this may be obvious but, well, here goes. I know that the pressure in a radiator has to be below the "operating" or "drop-away" rating of the air vent for it to be able to open (for a Hoffman No. 1-A it is 1-1/2 psi). Here comes the question with the obvious answer: this also means that if you are over that pressure, the vent slams shut, right? So in my example with the Hoffman 1-A if the pressure gets to say 2 psi before the radiator is completely vented, well, it won't get completely vented. So, do you really need to keep your entire operating pressure range below that rating (in this case 1-1/2 psi)?

Steamhead

As long as

the pressure can drop below that point, the vent will re-open after it has closed. I haven't been able to slam a 1A closed by blowing into it, not sure what it would take to do so. But a Gorton #D is a different story. It's pretty easy to blow that one shut.