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Pressuretrol cutout

RuffinoVino
RuffinoVino Member Posts: 52
edited March 2023 in Strictly Steam
Why does it matter if the cutout dial is set to 1 or 1.5 if everyone says the boiler should(will almost never) reach above that pressure anyway before the thermostat hits the set point? How would the differential dial set to 3 or higher effect the boiler performance if the boiler will shutdown when the thermostat is satisfied?

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    Depending on the control you are talking about, the differential may be subtractive or additive. If the control is set at 1 PSI and the differential is set at 1.5 PSI on the additive control than the burner will cut off at 2.5 psi and the burner will relight at 1 psi.

    If the control is subtractive and you set the control at the same settings you may get one cycle then no heat. This is because the the burner will cut off at 1 PSI and must drop to 1.5 PSI to come back on. But 1 PSI minus 1.5 PSI = negative 0.5 PSI. You will never get there

    So, what pressure control are you referring to?

    Second thought. If your steamer is sized exactly right, or even a little undersized, and you het heat to the last radiator with the boiler pressure never going above the limit setting, then you are one of the lucky ones that have the perfect, most efficient steam system one can imagine. Having just enough pressure to get the system up to temperature to heat every radiator in the building without going above 2 or 3 PSI is a good thing.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Jamie Hall
    Jamie Hall Member Posts: 23,272
    If the boiler were sized to match the system, @RuffinoVino , you are quite right -- it would make no difference, since the boiler would never reach even a pound, never mind higher.

    Unfortunately, this is the real world -- and finding such a creature is nearly impossible. There may be a few out there, but very very few. In the real world, it is necessary to shut the boiler off before the system pressure rises too high -- not only to save fuel, which it will, but to prevent cumulative damage (if not one shot damage) to other system components.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • RuffinoVino
    RuffinoVino Member Posts: 52
    So setting the differential at roughly 1 1/4- 1 1/2 is good?
  • RuffinoVino
    RuffinoVino Member Posts: 52
    Here is the settings for the cut in and cutout 
  • 109A_5
    109A_5 Member Posts: 1,385
    edited March 2023
    Hello @RuffinoVino,

    I have one of those very few rare examples Boiler SQ. FT = 300 and the EDR = 347. So my radiators will dissipate the heat faster than the Boiler can get it to the radiators. My pressure never goes over 2 inches of Water Column (2 WC = 1.156 Oz). My Pressuretrol never trips, regardless I have it set as low as it will go Cut-in = 0.5 and the Differential = 1. In other cases there is no usefulness making any higher pressure (assuming your system can and will). So in my case it is just a safety device in case the steam main plugs up or something bizarre happens.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • RuffinoVino
    RuffinoVino Member Posts: 52
    I just lowered the differential a little closer to the number 1  as shown in this picture. Does this seem good or should it be slightly higher?
  • 109A_5
    109A_5 Member Posts: 1,385
    edited March 2023
    Hello @RuffinoVino,
    If your boiler cycles on pressure, I would have the settings as low as they go that maintains reliable operation of the Presuretrol. Some Presuretrols apparently behave oddly at the minimum settings. Mine does not and it does not cycle anyway.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • dabrakeman
    dabrakeman Member Posts: 552
    Your current setting should be fine. It would still act as a backup safety device. Maybe your 3 year old grandson (don't mean to assume your age) decides to go around the house shutting off half your radiator valves. Then you would effectively have an oversized boiler like the majority of us ;) At the very lowest setting sometimes the pressuretrol can get a bit finicky. Most tend to let the pressure go a bit higher than the actual setting but I guess some could also go the other way shutting off the boiler somewhere close to the set cutout but then not letting it start back up if set too low. You could test it by making like a 3yr old yourself and shutting a quantity of radiators off at the valve and then jack the thermostat temperature up. You should after 30-60min or so witness the boiler shutting down on pressure and then restarting at the cut-in pressure as the thermostat is not yet satisfied. I don't know if you have a low pressure gage on your boiler or just the 30psi gage to witness the actual pressures since the 30psi gages most of the time are not sensitive enough to show you 1.5psi or 2psi. Then go take the handles off the radiator valves as you see so often done :)
  • PMJ
    PMJ Member Posts: 1,265
    edited March 2023

    If the boiler were sized to match the system, @RuffinoVino , you are quite right -- it would make no difference, since the boiler would never reach even a pound, never mind higher.

    Unfortunately, this is the real world -- and finding such a creature is nearly impossible. There may be a few out there, but very very few. In the real world, it is necessary to shut the boiler off before the system pressure rises too high -- not only to save fuel, which it will, but to prevent cumulative damage (if not one shot damage) to other system components.

    No reason at all that most systems out there should never reach more than a couple ounces of pressure. All this angst over boiler size. Simple control change tames all these boilers quite easily. A tstat stop or a pressure stop are the only control options the industry ever explored in all these decades? It truly is astonishing. The dead men are so disappointed.

    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    Your particular pressure control has the additive differential. that means that if you set the pressure to 1 PSI and the differential to 1.5 PSI the boiler must reach 2.5 PSI to cut off. Then the boiler pressure must drop to 1 PSI to turn the burner back on.

    Not that it matters on your system that never gets to even 0.5 PSI, and heats the home comfortably. You just need that control to satisfy the code and safety requirements of the industry. You also have a blow off valve (safety valve) that will never operate and a 0-30 pressure gauge that will never move. That is all because the code requires those items before a manufacturer can sell you that boiler. You have a unique situation where you do not have an oversize boiler that makes too much pressure then needs to stop the burner so the radiators can catch up.

    You should thank that installer...
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    How is this question any different that the other? The pressure control has no affect on the burner. The burner you have will heat all the radiators without ever getting to a half pound.

    Your system needs to actually build pressure before the pressure switches do anything.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • RuffinoVino
    RuffinoVino Member Posts: 52
    Well from a logical standpoint of the cut in means at .5 lbs of pressure the boiler will be allowed to turn on then the boiler must generate some pressure correct?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    your previous information states that your boiler does not generate pressure high enough to cut out with the control you currently have. Are you just trying to understand how things work, or are you trying to get the boiler to operate the pressure control?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Chris_L
    Chris_L Member Posts: 336

    Well from a logical standpoint of the cut in means at .5 lbs of pressure the boiler will be allowed to turn on then the boiler must generate some pressure correct?

    No, this is not correct. The cut-in only applies after the cut-out has been triggered. (In other words, the cut-in is the pressure at which the boiler will turn back on after it has cut out.)

    If the boiler never cuts out, the cut-in doesn't do anything. The switch is always on and the boiler runs whenever the thermostat calls for heat.
  • RuffinoVino
    RuffinoVino Member Posts: 52
    Chris_L ok now I understand..I was under the impression that cut in was always the pressure point the boiler needs to be at or under to turn on. So if that's the case and the boiler pressure never reaches 1.5 under normal conditions why is it so important to have the cut in so low? 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    edited March 2023

    Chris_L ok now I understand..I was under the impression that cut in was always the pressure point the boiler needs to be at or under to turn on. So if that's the case and the boiler pressure never reaches 1.5 under normal conditions why is it so important to have the cut in so low? 

    If you want to have a maximum pressure or 2 or 1.5 and you have the control you have, then you need to use the lowest pressure of 0.5. If you were to use say 3 as the cut in and 1 as the differential then the pressure control would never be able to shut off the burner at 2 PSI. You can't add enough differential to 3 in order to get 2. The number 3 plus anything will always be higher than 3.

    So to have a maximum of 2 PSI you must use a cut in less than 2 to get there. If you want a maximum pressure of 1.5 then you need to have a cut in of less than 1.5.

    Does that make sense?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics