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Thermostatic valve before radiatorvent.

One pipe steam, many radiators have a Danfoss thermostatic valve (with dial) mounted in the vent tapping and then a radiator vent mounted.
First thought was nifty but how could it work?
If the room is warm when the heating cycle starts the valve would be closed but what happens after you have let the air out of the radiator? It seems to me that closing the valve would not change anything.
And what about after the cycle is complete and the room is to warm?


  • DWood
    DWood Member Posts: 60
    Danfoss 1 Pipe Steam

    Good catch. The Danfoss 1 ps valve has a vacuum breaker built into the valve body to allow air back into the radiator when the system goes down to 0 psi or vacuum. You would need to cycle the boiler at least once an hour to allow this to happen. In smaller buildings, a regular thermostat is sufficent, in larger buildings it would require an analog clock or reset control.

    I've attached a data sheet on the Danfoss 1 pipe steam valve which shows the vacuum breaker and breifly talks about the theory of operation.

    Let me know if you have more questions.

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