Pressuretrol Mercury Switch??
First an admission. I’m far from an expert… just a property manager with a problem. In one of the buildings I manage, the steam boiler has the typical set up of a Pressuretrol (with a mercury) switch, a grey box that says “Cut in” and a high pressure emergency pressuretrol. The problem I’m having is…
First an admission. I’m far from an expert… just a property manager with a problem. In one of the buildings I manage, the steam boiler has the typical set up of a Pressuretrol (with a mercury) switch, a grey box that says “Cut in” and a high pressure emergency pressuretrol.
The problem I’m having is that if I set the mercury switch to cut out at under 5 lbs, the mercury tube doesn’t come back far enough after the boiler turns off to allow the system to come back on again. That is, the mercury switch stays in the “left-side down” position instead of flopping back to the “right-side down”.
The system works fine on just 2 lbs of pressure, so having it stay on until it makes 5 lbs is just a waste of fuel. After all, once the pipe gets to 200 degrees or so, it’s not going to get much hotter.
I know I’m overlooking something, but I can’t figure out how to solve this. BTW, the Pressuretrols are not quite level so at first I though that might have something to do with it, but it seems to me that leveling it perfectly will make it even harder for the mercury switch to flop back over (as it’s tilted a bit toward the right looking at it face on.
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Is there only one pressuretrol? There may be two with one being a reverse-acting unit to trigger a Heat-Timer or something.
There is no benefit to having the pressuretrols not mounted level. In fact they need to be positioned so as to move forward and backward with the pigtail as it heats and cools, uncoils and recoils.
Having it tip from side to side with those motions renders the settings inaccurate.
Anyway, with the boiler off, try setting the main to 2 and the differential to 1.
Does the pressuretrol you are adjusting have a seperate adjustment for “main” and “differential”? What’s the setting on your differential scale? And does it say “differential is subtractive” somewhere on the unit?