BOILER PRESSURE

PTTG40

Its seems to be the consensus in a residential home to set pressure as low as possible. I have a gas fired Dunkirk steam boiler.

For a novice can someone please clarify the differences between the pressuretrol, the cut-in and the internal pressure gauge and what its reading means. What is condidered the main and what are there functions. Pictures attached.

I mentioned in a previous post that when I lowered the cut-in to .5 from 2.5 and the pressuretrol from 10 to about 5, when I turned the heat up the boiler didnt fire. I then reset it and moved the cut-in to 2 and pressuretrol to 7 and it fired on right away.

Thank you

Steve Nichols

Why two Pressuretrol devices.

Okay, disclaimer first - I am a homeowner who loves steam and loves to tinker. That being said, why are there two pressuretrols on the system?  Both units shown in the pictures posted are both pressuretrols, with the newer type in the leftmost photo.

The photo on the left is similar to what I have but it has two scales on it, a differential scale to the right of a main scale.  I see your main scale is set at about 5 but I don't see any mechanicals associated with the differential scale.  Are you running the older style grey pressuretrol as your "cut in".  If so, that pressuretrol also has an internal dial wheel that is either additive or subtractive. 

I'll attach a picture of how my p-trol looked when it arrived, before I reset it.



Methinks there are some wiring issues between these two units that are causing it not to operate at the lower limits attempted.  I am sure several pros have seen this before and can chime in.  You did refer to a previous post, so apologies if I am missing some of the prior information.

Jamie Hall

Two pressuretrols

are quite common (or a pressuretrol and vapourstat) -- it's a safety measure.  In the present instance, the pressuretrol with the clear cover is a manual reset version (the little red pushbutton is the tip-off -- as is the lack of a differential scale) and appears to be prudently set at about 6 psi.  Maybe 7.  But it's in a good place.



The other one is older, I believe.  Whether that is true or not, that type of pressuretrol is almost impossible to set below a cutin of 2 psi, which is where it appears to be set.  They are unreliable at best below that, even if they don't fall apart (which they sometimes do...).



Is the picture of the pressure gauge taken when the system shuts off on pressure?  If so, the pressure is a little higher than I would have expected, but could be due to one of two things: either the gauge isn't spot-on at low pressures (quite common) or the "other" pressuretrol is the additive type -- but I'm inclined to the gauge not being spot on.



If you want lower pressures -- and it wouldn't be such a bad idea -- you could substitute a vapourstat for the older pressuretrol.

Steve Nichols

Thanks Jamie

for explaining the dual p-trol setup.  I always love hanging out on the wall and learning more and more. 

PTTG40

Internal pressure

Thank you for the response. That pressure reading was taken after the boiler just shut stop firing. It hits about 8 or so when on and decreases as its been off towards a one or two. If not zero.