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Fixing an existing Two-Pipe Air Vent System

are the pumps there to begin with? Are they really needed?

The only reasons I can see for the pumps are:

1- someone added radiators that were too low for gravity return to the boiler, or

2- a buried return failed, and someone decided to run a new overhead return fed by a pump.

If you can't get rid of the pumps, make sure steam cannot reach them. You must trap the drips from the steam mains separately from those on the returns. On the returns, if you use traps, use plain float traps (without "Thermostatic" elements) since they should not pass any air. You can also use water seals at least 5 feet deep on the returns (and keep the pressure LOW), for the same reason. These would eliminate some moving parts. There's no need to install a trap on each radiator, since the air does not vent into the returns on this system.

The Danfoss 1PS steam TRVs are the right ones to use on this system. Use standard or adjustable vents on radiators where TRVs are not used.

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  • Shawn Mansfield
    Shawn Mansfield Member Posts: 1
    Need Advice on Fixing an Existing Two-Pipe Air Vent System

    I am an HVAC Contractor in Illinois, and I have been called into help correct service and energy efficiency issues at a Chicago Church. The existing church has what I have determined to be a Two-Pipe Air vent system. The system has a number of traditional 1-pipe steam radiators and the rest of the system uses the 2-pipe design(both low on radiator and coming from the same main pipe with no trap and 1PS air vents on radiators). At some point (2) small condensate pumps were added in the basement (needless to say they are going through a lot of float mechanisms. The condensate pumps are on (2) of (5) total returns, so (3) returns are still just gravity based. The church would like to reduce the service issues they are seeing, provide better control, and reduce energy usage.

    I am not sure if Danfoss 1PS radiator valves would work with the existing piping arrangement? Can anything other than adding traps to every radiator (35) and main vents to the entire system be done to protect the condensate pumps? Would an trap mounted above the boiler water line on the condensate lines feeding the pumps help without any other traps? Would thermodisc traps work better on this type of system them traditional Thermodisc units at each radiator? Would using variable air vents work just as well as Danfoss 1PS in this type of system?
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