Pressure Setting for No Vacuum or Not?

Big Al

Thanks again for all of the great answers to my other questions! I have another fine tuning question:

When I bought my house with single pipe steam, the Pressuretrol was set at 2 PSI. (It is a subtractive type.) After doing my reading, I decided to try to turn it down to 1.5 PSI with the differential turned all the way down to 1 PSI. In theory, this should have the boiler turning back on at 1/2 PSI, but I don't know how accurate the device is at the lowest settings.

The boiler is pilotless natural gas and has a motorized flue vent damper. There is a brief delay from getting the signal to fire and actual ignition . . . I assume from some kind of safety circuit. Although the boiler seldom needs to run long enough to hit the high pressure limit, I noticed that with the Pressuretrol set to come back on at 1/2 PSI, by the time the boiler gets cooking again, sometimes the vents have already started sucking in a little air. I turned the high limit back up to just under 2 PSI and now the system never goes into vacuum breaker mode until the thermostat is satisfied.

I don't want to drop $200 on a Vaporstat this year. For now, I'm stuck with a 1 PSI minimum differential. Sooooo. For now, is it better to run the system from nominally 1/2 PSI to 1.5 PSI with a little air getting back in . . . or to bump it up a little and stay under positive pressure conditions? Why?

don_52

Maintain

Big Al,

Yes maintain, I would just "bump up" the differential until
it held. This of course will reduce your differential, next
just ease up the main a little at a time till you have
the "spread" you want.

As to why, you won't have to vent that air again, more important is the fact that when you hear the vents suck
after the steam collapses ( vacuum ) the mains are still
closed, right, if you have to re-vent the mains with
the main vents closed you can only vent through the rads,
take longer, but not a whole lot.

The point is once the system is picked-up and charged
you want to keep it there as long as possible, this
is the reason the bimetallic rad vents are preferred by
many over the float style, they hold longer.

HTH, db