dead loop in 2 pipe steam

Steamhead (in transit)

get out of the dry return?

If the dry return can't vent properly, you'll have air coming at that #41 vent from two directions- the steam main and the dry return.

Look for the vent on the dry return, and make sure there are no water pockets between the UH and the vent.

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Malcolm

dead loop in 2 pipe steam.

I have a recurring dilemma in the loop that rises from the ground floor to the unit heater in my office area. Sometimes it works and sometimes it doesn't. The riser to this unit heater is next to a dead end in a header. The end of the pipe on the first floor is trapped. All looks to be as it should be. The problem arises when I began lowering the system steam pressure according to the teachings of Dan. I had the boiler running to about 4 psi cutout and 1/2 psi or so cut-in with high fire adjusted to only trip if there is 0 psi.

everything else in the system which is a mix of rads and unit heaters, works but the heater in the most critical space - my office - is hit and miss and this is where the system thermostat is located.

Noodling this problem it seemed to me that there could be an air lock in this loop which is preventing the steam from rising up from the floor below so I concluded that if I put a thermostatic air vent at the top of the loop the steam will shoot up the pipe and away we go.

Received the vent valve (Hoffman Mod 41) yesterday and installed it at the top of the loop just ahead of the heater today. Turned the system back on and listened to the air being expelled from the vent as the steam came up - Oh boy! problem solved! NADA. The fan has come on a few times since but just blew cold air. The steam pipe is hot about half way up from the floor below but that's it.

Next I concluded that the only way the vent could be ineffective is if there is a lake in the steam pipe so it can't see steam. Went down stairs and started to measure slope from the second 90 after it has left the boiler room - runs down hill all along that wall. Checked the last 10' before the dead-end trap and it is level.

So I lowered the trap an inch or so and it started to buzz away and I thought Yahoo I got it! NADA...

Can anybody see what the hell is going on here? I have the pressure jacked up to about 6 psi which was making the heater work sometimes but since I installed the vent nothing.

Malcolm

Malcolm

Thanks for the reply.

Since I sent the message I took the 41 out and plugged the hole I drilled to install it. The system is now working the way it was which is to say that the UH does eventually come on when the steam pressure is up around 4 to 6 psi.

The fan comes on sometimes but the UH blows cold and the pipe to it is warm only half way up to the UH even though the fan only runs when there is pressure in the pipe!

Are you suggesting that I put the vent on the return side of the trap? I thought the vent will only close if it is hit by steam?

Malcolm