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How does pressuretol work

acl10 Member Posts: 344
Can someone exolain to me how the pressuetol works. When does it shut the boiler? When it shuts the boiler is steam still flowing into the pipes? If its on higher pressure does it run the boiler more?


  • BobC
    BobC Member Posts: 5,184

    The pressuretrol senses the pressure inside the system and shuts the boiler down when the pressure reaches the cut out point. The steam starts to collapse and the pressuretrol will turn the boiler back on when the pressure reaches the cut in point - assuming the thermostat is not satisfied.

    You want to run the system on as low a pressure as will fully heat the house on a very cold day. Any more pressure than that and you will just burn more fuel to build steam the system can't use and don't forget low pressure steam moves faster than high pressure steam.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • importance of steam pressure

    the pressuretrol on a boiler is like a cruise control on a car. when the thermostat fires the boiler, the pressuretrol keeps turning  the burner off and on to maintain the pressure in certain limits.. the upper limit should be no higher than 1.5 psi, and the lower point where the burner comes on is usually set to .5 psi.

    even these low pressures are not low enough for me, so i have a vaporstat, whose operating range is set to 2-8 ounces which is plenty to get steam up to the 55 radiators in my system. if i still had a pressuretrol, and the system pressure went up to 1.5 psi, i would be wasting gas needlessly. the vaporstat is more expensive than the pressuretrol, and maybe that's why people are reluctant to install them, and are content to give the extra money to the fuel fuel company.--nbc
  • haaljo
    haaljo Member Posts: 112
    But how does these gizmos work?

    Looks like a piston attached to a cylinder that is sensing pressure and lifting piston. But what's in the cylinder? Hackers want to know how to reduce cut-in pressure (and differential as well).
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Actually a diaphragm

    Instead of a piston, the pressuretrol uses a diaphragm to sense pressure. On the bottom of the diaphragm is a sealed chamber which connects to the pigtail. Steam pressure acts on the bottom chamber and pushes the diaphragm up. On the top side of the diaphragm pushing down is a lever and spring arrangement which counteracts and balances the force of the steam pressure below. Connected to the lever is a microswitch that is activated when the steam pressure is sufficient to overcome the force of the spring. Adjusting the spring tension determines how much steam pressure is necessary to overcome the counteracting force of the spring and thereby let the lever move and activate the switch.

    A vaporstat uses a much larger diaphragm, so a greater area is acted upon by the steam pressure and therfore  less pressure is necessary to activate the switch.
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