Identifying Burner Mod control

CMaxwell

hey, I am pretty sure this pressuretrol is used for burner modulation but I don’t know much more about it than that. How do you set it? What are the settings? And is there another name to identify this other than pressuretrol?

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mattmia2

It is this series. Since that is a large commercial burner you should get someone that understands the controls to help you.

https://www.supplyhouse.com/Honeywell-L91B1035-Pressuretrol-Controllers-Modulating-0-psi-to-15-psi

EBEBRATT-Ed

L91B with a Webster burner.

Set the main setting on the modulation control at the pressure you want the burner to start to modulate.

For instance your operating pressure control that shuts the burner on and off would be set to shut the burner down at 5psi and back on a just above 0.

Then the modulating pressure control would be set on the main scale at 2psi.

Then you get the burner running and play with the adjustments on the L91. You want the burner to start back to low fire at 2psi gradually dropping the flame size to try to = the steam output. The burner should drive back to high fire at 1/2 a psi.

ScottSecor

I agree with Ed's comment above. On some boilers you want the firing rate to adjust very fast as the pressure might build very fast (call it fast reaction time). On other boilers, you may want a slower reaction time.

For faster reaction time for high to low fire you set the differential to A.

For slower reaction time for high to low fire you set the differential to C or D.

In most cases, our goal was get the burner run times longer. With longer run times there would be fewer short cycles, allow the steam to reach the farthest places, etc. Typically, the burner would fire at low fire, sit in low fire hold for a short period, run up to high fire and then slowly modulate down to low fire and sit at low fire for a long time as pressure built very slowly.