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Pressure buildup one pipe steam

fsk Member Posts: 31
For the pros:
I am a HO and an avid reader of this forum.
I need some advise.

Mine is an old Oil boiler,with a beckett burner.

What I usually observe is the following:

The boiler runs and after a while,it cuts off at 2.5PSI.When the pressure drops to 2 PSI it kicks back on and keep doing it until the thermostat stops calling for heat.
Is there nay way to balance this system so that it doesn't cut off at high pressure.

I mentioned this to my oil dealer,who also services the boiler and he thinks that it is normal and there is nothing wrong.

I will appreciate all replies.



  • ttekushan_3
    ttekushan_3 Member Posts: 958
    Perhaps steam volume

    is exceeding the venting rate. One pipe or two pipe system? Usually a shutoff on pressure early in the cycle indicates the venting rate isn't good enough. After the first shut down, all the radiators are getting steam and condensing, preventing pressure buildup until all the vents or traps close and the radiators are really really hot. This is why it can continue to run until the t-stat's satisfied. The air in the system early in the cycle is non condensible and therefore a cushion rather than a dynamic fluid. If the system vents are too small, this can happen.

    Overfiring will also cause the same symptom as thats the steam volume half of the volume/venting equation. Perhaps the boiler's a bit overfired for the load?

    BTW, I'd turn up that differential control to 1#. Inside the pressuretrol there's a differential wheel. I'd be inclined to set the differential to 1# and lower the main (cut-in) to 2 to see how it runs. Any more pressure than is necessary for proper balance and heat distribution tends to waste energy. Commercial/industrial arrangements with unit heaters, etc often require higher pressure, but most residential systems can and do work well even with ≤1# pressure.

  • If it keeps doing this

    you may wish to have the burner nozzle size decreased slightly.

    Also, do the radiators toward the ends of the mains hear more slowly than those close to the boiler? If so, you need bigger main vents, like Terry said. Measure the length and diameter of each steam main and tell us what vent is on it.

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  • Dave_4
    Dave_4 Member Posts: 1,405
    It would appear...

    the pressuretrol differential (the lttle white wheel inside the control) is set a .5 lbs.

    Rotate that knob to 1.5 lbs. The end result should make the off setting still 2 p.s.i., but the "back-on" should become half a pound. This will do a bunch of things:

    First, it will reduce short-cycling (short cycling is always a bad thing); should reduce fuel consumption (that's a good thing); and, should you have any rad vents unable to "drop away" from the existing pressure, they will be able to at 1/2 pound.

    Of minor interest/concern: Most pressure gages cannot read the smaller pressures you are focussed on. Most P404 Honeywell pressuretrols (the one you most likely have) are incapable of bein precise in the realm you are exploring. Make sure the adjustment from 1/2 pound to 1-1/2 differentail ALWAYS allows the pressuretrol to go back to the "on" click - when the settings are in the half pound range. If it "hangs" and does not return to the back "on" setting, you wnet to far with the differential setting for the age and condition of the pressuretrol at hand. To correct that possibility (of "hanging") simply raise the white wheel setting to a slightly smaller differential from the one and a half pound setting suggested.

    Let us know how you make out. The ultimate solution would be a pressuretrol that IS designed for exactly what you seek; e.g., 1/4 lb on, 1-1/2 off. That Honeywell part # is 408J-1009 Homeownwer priced at ~$180. (labor not included).
  • fsk
    fsk Member Posts: 31
    this is a one piep steam system

    Heating 1500 sq ft.

    It has only one main and all radiators heat very well.

    When the system starts,it doesnt cut off.It starts cutting off(and often) after it had run for atleast 30 minutes.

    Is there any trick to find out the nozzle size on the burner.I know its a Beckett AFG burner with an initial firing delay solenoid on it.The problem is that every time a new service man from the dealer comes for service and I see that he hardly cares for the nozzle size.The last time the guy came he just put what he had in his van..but than all the oil companies here are sloppy..unless i find a dependable oil service man who I can deal with out side of the oil dealership..
  • Where's \"here\"?

    tell us where you are and we might know of someone who can do better. Also try the Find a Professional page of this site, under Resources above.

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  • fsk
    fsk Member Posts: 31

    I am in northern NJ.
  • Call Palmer Heating

    in Rahway, they're listed in the Find a Professional page of this site- click Resources above, then Find a Professional.

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