Pressuretrol Post Revisited
I’ve added a photo to make this post clearer as to what boiler controls I have. Here was the original post: 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…
I’ve added a photo to make this post clearer as to what boiler controls I have. Here was the original post:
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.
Guys.. as far as I know, none of the controls have anything to do with high fire/low fire. The boiler always runs on high fire (unless I manually set it at low during non-heat season)I’ll play around with the controls and see if I come up with any further info for you.
Give a call some time! Or wait for another one of those B’Stoner get togethers. First round’s on me.
Hey MP,
I think you know your ish, you’re alright in my book! Sometimes I get a lil ahead of myself and you got me. The pigtail should definitely be turn 90 degrees. As far as the cut in/out, if the L91 is modulating at 2 psi then you would want the burner to cut in when the pressure drops below the setpoint. So here we have a 2 lb setpoint with cut in at 1 to 1-1/2 lbs. The boiler theoretically should never reach above 2 pounds and unless there is no load, should never shut off.
Of course I am an industrial/process guy and we love these kinds of scenarios. In a building, that would be a nightmare. Upon which discovering this condition you would want to call in a guy with a fancy shmancy camera that can take pictures of where all that heat is going!
Hey, I am looking forward to meeting you one of these days.
And thanks for checking me. I dig it.
-Steam Man
SteamMan, I’m a hot shot residential guy and I’m sure you work on a lot more industrial burners than I do, but 5 psi cut out-1 psi cut in sounds like a lot, no?
Also, it needs to be said that the middle pressuretrol, since it is mercury-bulb activated, needs to be mounted like the one on the right so it tips forward and backward as the pigtail expands and contracts as opposed to tipping side to side.
That’s all I got.
BTW
The other possibility is you have a Low-High-Low burner and the pressuretrol is again selecting the firing rate. On second look, it seems that is the case anyway, let us know what the models #s are. I am tired of typing 😛
-Steam Man
I can’t see exactly what you have there but I am going to assume the following.
From the pic it looks like your pressuretrols are operating, modulating and high limit. The high limit is the one with the red button (IOW manual reset). The manual reset does not need to be adjusted, leave it set at 10 lbs.
The modulating control will attempt to modulate your burner to maintain the pressure you set the control at. That is, it will automatically tell the burner to go to high fire or low fire or any point in between to maintain the setpoint of your pressuretrol. It will have 3 terminals with a wire to each.
The little grey PA404 is your operating control. Set the cut-out at whatever you want, then open the case and set the dial at whatever pressure you want the burner to kick on(cut-in)at.
So now that you know what the Hell everything does, here is what to do.
Set the PA404 at 5 psi cut-out, 1 psi cut-in. Set the modulating control at 2 psi.
That’s it….
If this doesn’t fit what you have there, write down the model numbers of the pressuretrols. The gray one is a PA404, the other two start with L.
Good luck.
-Steam Man