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Steam System Question

hydrohead Member Posts: 10
I have included pictures of parts located in a steam boiler system that one of my clients have at their home. I am wondering what exactly these particular parts do. Can someone help me figure out how these controls work.


  • Jamie Hall
    Jamie Hall Member Posts: 22,917
    Picture 4 -- is a moderately typical radiator valve for a vapour steam system. 7 is a -- or more likely the -- main air vent for the system. I can't read the markings, but it's a big one. Unless it's been abused, probably still works. 6 is a control -- probably a thermostat, but... what's it connected to? Picture 1 is a Sarco trap and air eliminator. It probably still works, too... Picture 5 may be a type of thermostatically controlled radiator valve... Picture 8 is a perfectly normal Sarco thermostatic steam trap. Picture 2 is more or less the same gadget as picture 1. And picture 3 is ditto -- note the sight glass on the trap which is much too dirty to read the water level in the trap...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,490
    #6 and #5 go together - a remote controlled thermostatic radiator valve.

    All the rest, what Jamie said.
    Retired and loving it.
  • retiredguy
    retiredguy Member Posts: 883

    f f

    This is an explanation of the device in pictures #2, 3, & 6. These were common on very old systems. When they worked they were great and when they failed they weren't too hard to repair if you could find or make the parts. Hope I got all the necessary explanation.

    A two-pipe vapor system with a return trap

    Figure 3-6. - A two-pipe vapor system with a return trap.

    mechanism, which permits equalization of the boiler pressure and the pressure within the return trap.

    Vapor-steam systems with return traps are similar in design. However, it is seldom that two installations are alike. Since the details differ with the type of heating equipment, it is recommended that the manufacturer's installation instructions be followed.

    However, the mechanical return trap should be installed on a vertical pipe in the return system that is adjacent to the boiler. The top of the trap should be level with, or below, the bottom of the dry return main. The bottom of the trap should be approximately 18 inches above the boiler waterline to provide a sufficient hydrostatic head to overcome friction in the return piping to the boiler.

    The two-pipe vapor system with a return trap alternately fills and dumps. It returns condensate to the boiler by a mechanical alternating-return trap instead of by gravity. The alternating-return trap consists of a vessel with a float that, by linkage, controls two valves simultaneously so that one is closed when the other is open. One valve opens to the atmosphere; the other is connected to the steam header. The bottom of the vessel is connected to the wet return.

    In operation, when the float is down, the valve connected to the steam header is closed and the other is open. As the condensate returns, it goes through the first check valve and rises into the return trap, which is normally located 18 inches above the boiler waterline. The float starts to rise when the water reaches a certain level in the trap, the air vent closes, and the steam valve opens. This action equalizes the trap and boiler pressures and permits the water to flow by gravity from the trap, move through the boiler check valve, and go into the boiler. The float then returns the trap to its normal vented condition, ready for the next flow of returning water.

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  • hydrohead
    hydrohead Member Posts: 10
    This boiler was replaced two years ago. It has a typical pressuretrol . should it have a vaporstat instead?
  • Jamie Hall
    Jamie Hall Member Posts: 22,917
    Probably. If it really is pretty intact, the certainly -- and the vapourstat should be set for starters at around 8 ounces per square inch cutout, 40 ounce (subtractive) differential.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Alan Welch