Main Vent Not Venting, Why ???

Bobby D.

Here is a photo of my one pipe parallel flow steam main, showing the feed to the last radiator and the main vent on a 6" nipple just after the riser to the last radiator.

The main vent is not venting. It is brand new, a Hoffman # 4A, the radiator vents are also all new, with Hoffman # 40's.

Many of the Hofffman 40's on the rads vent and close, and vent and close, but others just vent constantly, until I tap them gently to, and they stop venting.

Can anyone tell me why the main vent does nothing when the boiler starts, is running or shuts down. The boiler pressuretrol is set to cut out at 1.5 PSI and cut in at .5 PSI.

Does the nipple need to be higher ( there is no more room to raise it ) or is it to close to the riser for the last radiator.

Any thoughts ?

Thanks in advance !

Bob W._2

Hoffman 4A looks small....

Post the length of the main and the pipe diameter. One of the steam guys can calculate how much steam must be moved out of the main. I suspect they will recommend a Hoffman 75 or some big Gorton's, which are the best value. I've given up on Hoffman 40's on my rads except for the ones closest to the thermostat. Using 1A's (adjustable) and Gorton C and D's on the large ones.

Bobby D.

The main is 2 " in diameter and 29 feet long

Steamhead

The 4A is too small, Bobby

If you can get Gorton #1 vents, put a tee on the riser and install two, with an elbow pointing up for the second vent. If you can't get Gortons, get two Hoffman #75 vents.

Is that the only main in the system?

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Bobby D.

That is the only main on the system, it runs parallel to the main beam for the house ( a Cape ) Thanks for the advice.