Venting Problems

Dean_21

This is my first winter in a home with a steam heating system. The house has a two pipe steam system with a basic gravity return. All counted there are 8 radiators in the house and 9 steam traps. 1 trap is at the end of a cross over line between the end of my main steam pipe and the return. 7 of the 9 traps are Hoffman No. 18 traps in which I recently replaced the cage units with Barnes & Jones 2211 cage units. The other 2 traps are on radiators which I keep the supply valve closed. However I've noticed that there is a "Hoffman No. 1 Differential Loop" connected to the system. The top of the unit has a pipe connected to my main steam line and a Gorton No.1 Vent. The side of the differential loop is connected to the return line. I can hear air leaving the vent when the system kicks in, but the vent seems to get hot and close within a few minutes of the system starting and before the main steam line gets warm. Is this supposed to work like this? I can't find much literature on the differential loop. Should I have a different vent on top? It's taking 4 hours to raise the ambient temperature in my living room 4 degrees (thermostat is on interior wall). Any thoughts?

Steamhead (in transit)

You still may have a bad trap somewhere

The lines coming into your Differential Loop are as follows:

Top connection next to air vent- equalizing line to steam main or header

Side connection- dry return from radiators.

In this Hoffman "Controlled Heat" Vapor system, steam from the boiler fills the mains. Air in the mains is vented into the dry (overhead) return thru those end-of-main traps. As steam enters the radiators it displaces the air which exits thru the traps into the dry return. Air leaves the system thru the vent on top of the Differential Loop.

If the pressure difference between the steam main and the dry return exceeds 10 ounces, the Loop allows some steam into the dry return to maintain that maximum differential. This steam also closes the air vent on the Loop.

You will need to trace the steam back from the vent when it closes to find out where it's coming from. If it's coming from the dry return, follow it to the bad trap. If it's short-circuiting thru the Differential Loop, you'll have to remove this piece of heating history, cap the steam line and put the vent in the dry return connection. Also install a Vaporstat to keep the boiler pressure under 10 ounces.

BTW, since that's the only vent in the system I'd replace it with the much larger Gorton #2.

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