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# Basic Pressuretrol setting question

Member Posts: 264
attached pic is for a pressuretrol l404ftv model and i believe its additive

i guess if you set the main at 2 psi and the differential at 2, the boiler burner cuts off at 4.0

and when pressure hits zero on steam  boiler PSI guage, the burner turns on

if differential<span style="text-decoration:underline;"> or</span> main setting is reduced by 1 than the burner cuts off at 3

what is the purpose of the differential?

how do you set device to control when the burner turns on?

thanks

• Member Posts: 604
Settings

The main setting determines at what pressure the control cuts out. As is indicated on the scale plate, the differential is subtractive and determines at what pressure the control cuts back in. Main minus differential equals cut-in.

So for the settings shown in the photo, the control cuts out at a pressure of about 3 PSI, and cuts back in at (3 PSI main) - (2 PSI differential) = 1 PSI cut-in

• Member Posts: 17,011

is too high as it is set. Try resetting the main to 1.5, and the differential to 1. Your system should be much happier. If you can't go that low, go as low as you can.

To answer your specific questions, on a pressuretrol the main is the pressure at which the burner will cut out; the differential (subtractive -- says so on the differential scale) is the difference in pressure between where the system cuts out and where the system cuts back in. Therefore the main minus the differential sets where the boiler cuts back in.

If the differential were additive, then the main is the cutin and the main plus the differential is the cutout.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 5,227
Turn it down

I agree with Jamie that boiler pressure should be turned down, there is no need to run a residential steam system above 1.5PSI. That particular pressuretrol might not let you go much lower than 2PSI but the lower you can get the more fuel you will save.

I just got 151 gallons of oil delivered and that reinforces the need to save fuel!

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