Pressuretrol under estimating by 1 psi

JShep

To start; clearly I need a vapor stat… but I’ve got to assume in the short term I can dial things in through adjustment… so I’m looking for some thoughts on how to sort things out while I work on getting a vapor stat because it’s 28 degrees out.

short story; been tracking down return side hammer (full bore steam slugging along late cycle during longer cycles). While there is potentially other causes, it only happens north of 1.4 PSI, but my pressuretrol is off by ~1 PSI.

1.4 PSI, that’s too high! You’ll ask/say. I’m with you… But as I say there with my boiler and see things climbing, I said the same thing to myself… and my cut out is set at 1 PSI. Hence, we’ll proven story; it’s thresholds and tolerances just aren’t sufficient for a good steam setup.

So as I’m seeing this happen, I dial it down… still running, pressure still climbing… bang bang… dial it down more… (and so on). I’m about 2 minutes of trying to trace the exact origin of the hammer, I come back and am showing 5psi. ****. Flip the switch and shut it down.

pull 5 things off just so I can flush the pigtail on the Ptrol… not much in there. Reinstall everything, dial the pressuretrol all the way to its lowest point (which shouldn’t let it cut on, I’d assume, as the physics aren’t going to let me be less than 0 to let the cut in matter as it bottoms out at 0.5).

With the system off, I applied some leverage to the pressure plate and at full extension it wouldn’t trip the switch. so I pull everything off again and try my hand at breaking things by adjusting the brass set screw a turn or three to the point where minimal effort on the pressure plate causes an audible click of the switch… put it back in, adjust the main setting… I can get it to cut off.

the problem is, the pressuretrol set at what my eyeball gauge tells me is ~0.3-0.4 psi is where it effectively cuts off as my 0-5psi gauge reads 1.3 (not ideal, but much better than factory 25psi that never showed anything but 0)… so again; 0.5 minimum diff (it’ll screw lower, but the screw just pops up as the spring is at full rest with 0 tension to apply to the pressure plate, to release the cut off switch) means my cut in wants to be less than 0… so it won’t turn back on. Tweak the main up to ~0.6, I’ve again got positive cut in, but my cut off now is ~1.6 which is not only too high, but past the hammer inducing threshold.

so right now the heat is off, because now that I know my pressure was escalating so high, I’m no longer comfortable letting the system run unattended as I have no means of cut off without serious steam hammer pouring through the returns, shooting a torrent of condensate out my main vents.

I backed off the set screw a bit, was able to buy myself very close to not exceeding 1.4 (which again is not ideal, but not hammering, and not leaving my house without heat in sub freezing temps) … so should I bother with continuously trying to fine tune the set screw to get myself to a comfortable short term? I’m 99% confident my BlueFin 0-5 psi gauge is quite accurate. The needle moves smoothly, rests at zero, starts to show signs of life when I can hear the water start shifting to steam and leaving the boiler, and it hangs out pretty steady in the .6-.8 psi range for a good 10 minutes of boiler operation. So if the gauge is indeed correct and my pressure trip is short reading about 1 psi… is there some other adjustment beyond that set screw? Because regardless of bringing it forward or back, it isn’t likely to get me dialed in to a good range as 1.4 (where the hammer starts) minus 1.0 (about the amount it seems to not recognize/be off by) minus 0.5 (diff minimum) is never going to equate to more than 0 allowing it to cut back in.

I attached an old pic I took a few weeks back of the pressuretrol for model reference

JShep

Also… I’ve got a PA404 on hand (not sure the exact model) which a quick Google suggests may have slightly better lower end thresholds than my unit if supply house is correct.  It’s from the old boiler, so I could try messing with that when I get home and see if that gets me sorted… which I’m inclined to do since I just saw that vaporstats are $300.

ChrisJ

The questions I'd ask is, why are you getting hammering at all? You shouldn't be, not even at 5 PSI.

Is your pressure relief valve installed properly and in good working order?

Why is your pressure climbing this high regularly? Are your radiators and mains vented reasonably fast? Can you improve it? A correctly operating system shouldn't rely on a Pressuretrol to limit it, at least not constantly in every day use.

Can that boiler be safely downfired for less output?


If you're vented as good as you can get it, and the boiler cannot be safely downfired anymore, I'd look into a proper Vaporstat designed for 4 PSI and lower and stop trying to tweak one that's not intended for it. There are many mechanical differences between a Pressuretrol and a Vaporstat. I'd also want a good working Pressuretrol in addition to the Vaporstat on a separate pigtail.

ethicalpaul

That was my first question as well...setting aside for a moment that pressuretrols are bad (they are), why is your system hammering? Something else is going on.

Jamie Hall

Agree with the guys above. Fiddling with the pressure control is trying to conceal a real problem somewhere in your system, which you need to find. Then you can start working with the pressure control.

Chances are the one you have which doesn't seem to be working is flat out broken -- they can't be dialed below a certain amount before the linkage disconnects and you're done.

EBEBRATT-Ed

Don't walk away from the boiler without being 100% sure you have a working pressure control.

You could end up with a much bigger problem than loud returns.

JShep

ChrisJ said:

The questions I'd ask is, why are you getting hammering at all? You shouldn't be, not even at 5 PSI. Is your pressure relief valve installed properly and in good working order? Why is your pressure climbing this high regularly? Are your radiators and mains vented reasonably fast? Can you improve it? A correctly operating system shouldn't rely on a Pressuretrol to limit it, at least not constantly in every day use. Can that boiler be safely downfired for less output? If you're vented as good as you can get it, and the boiler cannot be safely downfired anymore, I'd look into a proper Vaporstat designed for 4 PSI and lower and stop trying to tweak one that's not intended for it. There are many mechanical differences between a Pressuretrol and a Vaporstat. I'd also want a good working Pressuretrol in addition to the Vaporstat on a separate pigtail.

To answer the direct questions; the system isn’t sufficiently vented, with two parts to it.  1) the prior boiler was way oversized (250k btu) for any reasonable use in what will be the next 10 years for us.  The previous owners had a boiler put in scaled to the full 5 floors, 6950 sqft of the house (for ~15 years, despite them living on one and a half floors of the mostly in progress restoration they never finished).  The top two floors are cut off from the system with gate valves, the entire rear building (three floors, 1800 total square feet, that once had 10 total radiators in it) was entirely rusted out as the mains were buried in the dirt under the first floor… separate heat was planned to be installed later apparently.  So in total, they were firing a 250k boiler for 6 rooms with a total of 7 radiators… only two of which were decently sized.  I assume they must have had the boiler considerably down fired to have it function.  So now that I’ve got an appropriately sized boiler (I’m up to 9 rooms, 11 radiators), but haven’t down fired it as, well, I haven’t gotten there yet because I’m actively working on rebuilding the whole system and I believe once I have sufficient volume for the steam to occupy by way of additional radiators, and traps to give the steam a place to condense beyond just back down the steam mains and risers by way of the condensate mains and risers, plus (the second and arguably considerable reason) is I just don’t have enough main vents, which I’m assuming the previous owners never got around to because they only ever did the bare minimum recommended maintenance and had a 2” main wide open venting through a couple of inches of dirt.

fully tracking a properly vented system should rely on a pressure limiting device for daily operation.  Presently, however, I’m both trying to periodically heat my house while actively working on the system… so I’m actively monitoring throughout the process and we turn it off when sleeping or not at home.  

So in the interim, I’m using a pressuretrol (that I have confirmed is working … the diff adjustment screw had separated from the mechanism, so I’m now comfortably 6 hours in with no banging as it’s properly cutting off at just over 1 psi and coming back on at near zero).  It’s not efficient, it’s not optimal, but I’m getting 15-25 minute cycles (actual heating time, after the point of steam from periods where it’s been off for a bit), so it’s not terrible.  And when at temp, it runs shorter cycles because it’s actually maintaining heat pretty well as I’ve been re-balancing things.   

Having removed and replaced the old boiler, redone all of the near boiler piping, sourced/stripped/installed 3 radiators (two of which went into rooms that had no radiators, but thankfully the original 1908 supply and return lines capped off under the floor that made for easy installs, one replacing a smaller counterpart, and one more very soon to be added), and done 20’ of main rework, 40’ of branch rework, and 20’ of riser rework… while I’ve been doing iron pipe work since I was a kid, damn if I’m not learning the half science, half voodoo the honest way… but I’m enjoying the learning process and appreciate all the input from so many people.  

Still more to learn, still significant work to accomplish… but thankfully, Frank and crew are slated to come out in a month to sort out the whole system… as long as I leave them with a sound enough setup to work on, but I’m confident it’ll get there.

I’m headed to the hospital for the next 36 hours (unrelated, not a big deal), but Friday afternoon should lend itself nicely to replacing the crossover traps in the basement and adding enough venting… doing the repipe work with the mains and risers that I’m doing, I’m making use of reducing tees/drop elbows in a number of keys spots as I think 115 years of changes to the house and radiator placement have caused significant potential for the need to redistribute where venting is happening… so I wanted to leave myself some connection points, one of which is going to make for a fantastically located flush port.

-Jeff
trying not to eff it up since 2023.

mattmia2

So if there are traps it is 2 pipe. I'm guessing that there are drips in to the wet return from the main and the higher pressure pushes the water seal out of those drips and puts steam in your returns.

The water line probably got lower as boilers were replaced so the pressure needed to push through the water seal is less than it was with the original boiler.

Jamie Hall

Sounds like you have the right ideas there -- keep it up!