Can a Pressuretrol be easily recalibrated by a non-pro? 0.5 min setting seems to cut-in at 1.5psi

Jim_NY

Have learned here that "lower" pressure settings are sufficient for steam (unless perhaps there are other challenges in play). And that Pressuretrols, though standard original equipment, are not precise (vs. Vaporstats).

Have bottomed out the Pressuretrol settings to 0.5 cut-in, and to 1 on the differential dial (down from 5 and 2). So, unless mistaken, set to cut-out at 1.5 psi and cut-in at 0.5 psi. No low-pressure gauge (yet), so made the "poor-man's manometer" with a barbed garden hose fitting on the drain, and a length of 1/2" ID clear tubing to the ceiling: it appears (using ~27" of water column = 1 psi) that actual cut-out is ~2.5psi and cut-in is at ~1.5psi.*

Is there a safe way for a Pressuretrol to be easily adjusted by a non-pro?

* (Takes quite a while of continuous firing to reach cut-out, but pressure drops enough in ~30 seconds to cut back in. This was timed experimentally with thermostat set unreachably high, so such short-cycling unlikely to occur in typical operation except perhaps on a really, really cold day.)

JUGHNE

First is your pigtail clear all the way into the boiler?
What your control sees and the hose sees may be different.

Jim_NY

Currently, as originally installed via sight glass valve. (A low pressure gauge there would be informative.)

JUGHNE

Did you ever take the pigtail off for cleaning?

Jim_NY

Not yet.
It does consistently cut out/cut in at the same water column levels/pressures, so presume it can't be completely blocked.
In a thread last month, it was recommended that - as currently installed - the course to clean or modify (add a low pressure gauge) was to cut and replace the existing pigtail.

Lance

Yes you can easily set it. Follow the MFG instructions. I have never been happy with this placement of the pigtail at the top of the sight glass pipe, But for the mfg. it makes a package. A better place I think would be off the top of the boiler or even on the steam riser. If I had to use this tee, it would be better on top and use a straight pigtail. Sadly this pigtail cannot be removed for normal maintenance and should be re-piped to allow the tail to be unscrewed. Boiler piping is the fitters job, not the boiler makers job.

EBEBRATT-Ed

@Jim_NY

Yes you can adjust it. The scale setting on the outside is the "CUT IN" this is when the boiler will restart if it has shut down on pressure

Example: cut in set at .5 psi, differential set at 1 psi the burner will "CUT OUT" or shut off at the cut in setting plus the differential setting.

Caution; it's possible that the boiler will not start or restart if you set the cut in too low. The scale settings are not that accurate

Jim_NY

Thanks to all for the comments. I've adjusted the title to be more clear that the cut-in set at 0.5psi seems to be actually trip at about 1.5psi.
The screw-down scale has been bottomed out, and don't wish to force it further down as posts here have mentioned the mechanism coming apart under such stress.
So was wondering if a non-pro could in another way adjust/calibrate it to bring the set pressures more in line with the measured pressures.

Jamie Hall

There is a calibration screw inside those things -- somewhere on the Wall there have been a couple of threads about it. You need a really accurate low pressure gauge and a stable low pressure source to do it.

Uthrid

I have read on here in many places also that the pressuretrol and the pigtail need to be aligned 90° to what you have pictured (if you have a mercury switch in the pressurtrol that is). The reason being that as the pigtail heats up it tries to straighten out which will tip the pressuretrol, and thus the mercury switch, and throw off the settings.
If this does not apply here will a pro please correct me.

ethicalpaul

No not that one, only mercury ones, if even then.

Jim_NY

Thanks again for the comments. Perhaps a non-pro without proper tools and standards might want to forgo this type of re-calibration. For those interested found the general procedure mentioned above is discussed here and other places by @Fred.

SteamingatMohawk

I bought a replacement and at the 0.5 cut in and 1.5 cut out settings, it actually cut in at 0.6 and out at 2.6.

Take the cover off and if there is a glass bulb with shiny fluid (mercury is not a liquid) in it, that's the mercury switch and you need to rotate the pressuretrol relative to the pigtail. It doesn't look like you have a lot of room, so good luck. I don't know when the design was changed, so it's hard to tell from the outside.

Since you used a home made test rig, the orientation doesn't matter in checking the settings, but in use as mentioned above the pigtail will tend to rotate with pressure. I haven't seen any data on how pressure makes how much difference in the operation.

@ethicalpaul

ethicalpaul said:

No not that one, only mercury ones, if even then.

How can you tell its not mercury?

ethicalpaul

I've not seen one with the gray metal box that was mercury, but I'm open to correction

Jim_NY

There seems to be some interest in the innards of this particular Honeywell PA404A Pressuretrol (169H Limit Control). The red arrow points to what I believe is the "locked-down" calibration screw described in posts by @Fred.

Jim_NY

Just found a Honeywell Tech Document on this model Pressuretrol and - unless misinterpreting - am surprised to see that the operating range for the subtractive differential PA404A is listed as 3-15psi. Also the "recommended minimum set point is differential setting +1-1/2."
However, it lists operating range of the additive differential model as 0.5-9psi, with no recommended minimum.
Seems the subtractive model may not be intended for lower-pressure systems.

SteamingatMohawk

Holy cow, for as many times as I have looked at that document, including yesterday, I never paid attention to that statement. This now makes the manufacturer's statement I mentioned above more reasonable, but incomplete, since they never explained the "why" the unit was in spec.

Thanks for your attention to detail.

So, given the choice is it the added differential pressuretrol or a vaporstat? What are the advantages and disadvantages of each?

Like I said the other day, this website is a place to learn something every day.

ethicalpaul

They are definitely not for low pressure steam regulation.

If my boiler were building pressure enough to trigger that pressuretrol, what I would do would be to ensure my main venting was good, and then install a low-pressure switch with a simple delay device to shut off the boiler for about 10 minutes if it gets to 6-8 ounces of pressure.

And I did!

SteamingatMohawk

See my comment in one of the other discussions about how my Cyclegard affects pressure.

Jim_NY

Since this thread is still active, just will add that had my searching here been more efficient, I wouldn't have been surprised at the manometer-estimated readings cut-out/cut-in for the Pressuretrol. Including from:
@ChrisJ in 2011 on a PA404A:
"It doesn't trip until around 2.5psi and then closes the contacts again as high as 1.5psi."
forward in time to
@EBEBRATT-Ed in 2022 on a PA404A:
"the lowest it will go is 2 1/2 CO and 1 1/2 CI"