Perfect 0.4 - 1.5 psi Pressuretrol you'll never guess how

ethicalpaul

OK I couldn't get my Pressuretrol low enough to cut in at .5 or cut out at 1.5. It would cut in at 1.2 and cut out at about 2.25. The indicator would bottom out in the cutout it rides in preventing any more easing of the spring tension. The solution? Remove the spring and indicator and the tension of the microswitch provided just about the right tension for a very nice cut in and cut out.

Check out the world's most boring video to see it in action (I spared you the beginning of the first firing cycle with this link -- right click to open these links in a new tab or window to have it respect the playback head position: https://youtu.be/sp688Jdc2zM?t=766 ). It takes my thermostat from 70f to 72f. See the video description for links to the interesting parts.

Questions: Is this short-cycling? Or just normal behavior recovering from a 2° setback? Why is 1.5 psi the magic cutout number? Why not 1.75 or 1.25? Can I "under-fire" ("down-fire"?) my boiler to make it cycle less? Why did the pressure drop during the initial firing cycle??? (see 15:48 at https://youtu.be/sp688Jdc2zM?t=948 )

ethicalpaul

I’m having trouble with the links from heatinghelp respecting the playhead position, but you can use the index in the video description to go to various points of interest.

I had an idea what causes the pressure drop mid cycle. I saw it happen again today. It might be that after the radiator vents close, and the radiators have like 1/2 or 2/3 steam, the pressure builds. Then the steam loses some heat to the cool part of the radiator and of course the room.

A rather large condensation occurs and starts flowing back, perhaps triggering more condensation and collapsing the pressure (it wouldn’t take much of this to kill the pressure in the system given the expansion of steam, which in my case is just fine for my burn time—maybe my system isn’t quite so oversized.

EBEBRATT-Ed

I would strongly not advise messing around with a pressure control to that degree....pulling out a spring, it's a safety control. Anything happens your homeowners insurance would run away and so would Honeywell.

Get a vapor stat or add a second control as a backup. The risk is on you and you alone.

The reason steam builds up and then drops is when you come out of setback the system piping is cold. Steam goes out into the system and for a moment condenses back to water due to the cold pipes faster than the boiler can supply steam. Vacuum from the condensed steam is pulling the steam out of the boiler. This stops as the system warms up

Fred

@ethicalpaul , I doubt that the Pressuretol will consistently work with the spring off. Here is the correct procedure to calibrate it, if you need it:

Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with). You may need to play with it to get it exactly where you want cut out to be.

neilc

is your, are your pigtail(s) clean ?

ethicalpaul

It’s clean at the time of that video, and now it’s re-piped with brass and a straight brass pigtail. Before I disassembled it the first time it was mud but still reading pressure

ethicalpaul

> @EBEBRATT-Ed said:
> I would strongly not advise messing around with a pressure control to that degree....pulling out a spring, it's a safety control. Anything happens your homeowners insurance would run away and so would Honeywell.
>
> Get a vapor stat or add a second control as a backup. The risk is on you and you alone.

I agree with you to an extent. On the other hand, all the spring is doing is making the pressure higher than it should be, so the control trips easier now and is safer than before. But I’ll try the adjustment.


> The reason steam builds up and then drops is when you come out of setback the system piping is cold. Steam goes out into the system and for a moment condenses back to water due to the cold pipes faster than the boiler can supply steam. Vacuum from the condensed steam is pulling the steam out of the boiler. This stops as the system warms up

Thanks, that makes sense, I had never read about that pressure dip anywhere before.

ethicalpaul

Here’s the brass setup with the straight pigtail. I have a small leak in the union at >1psi

Fred

Why did you strap that pigtail and the Pressuretrol to the conduit? It's not going anywhere.

mikeg2015

Just get a vaporstat and a low range pressure (16oz) gauge so you can verify it's working.

ethicalpaul

> @Fred said:
> Why did you strap that pigtail and the Pressuretrol to the conduit?

Because it’s a lot of leverage on the T that’s behind the sight glass and I didn’t want to bump it or have it fall over time from vibration. I’d rather this stuff not hang off the sight glass but that’s how I inherited it and I don’t see an obviously better place for it at the moment

Fred

mikeg2015 said:

Just get a vaporstat and a low range pressure (16oz) gauge so you can verify it's working.

He's got a 0-3 PSI gauge on there. That is good, even if he adds a Vaporstat.

KC_Jones

Also you should pipe the discharge on your safety relief valve down to the floor. Cleaning up that wiring wouldn't be a bad idea either.

ethicalpaul

You’re right, but I’m doing things as I can. You may have missed it in earlier posts, but I had zero main venting, all those wire nuts were INSIDE the Pressuretrol box which was being used as a junction box, my pigtail was full of mud, the 1/4” plumbing was steel and had rotted out and broke when I unscrewed it to clean the pigtail, so the relief valve which hasn’t activated ever is right after replacing a rusted out radiator and fixing two leaking radiator valves 😅

Chris_L

@ethicalpaul, You can read all about testing and calibrating Pressuretrols on this thread: https://forum.heatinghelp.com/discussion/159223/testing-honeywell-pressuretrols-with-custom-rig/p1

As for using a Pressuretrol without the spring, I've done it for years on a couple boilers. They work consistently fine. When the pressure is turned down all the way, the springs weren't doing anything anyway. (All the resistance to the boiler pressure was coming from the spring in the microswitch.)

Understandably, you are unlikely to find any pros who will approve of this since you are modifying a safety device. But I can't see any risk.

Now, on each of my boilers, I use a microcontroller with a pressure sensor to keep the pressure below 1/2 psi, with the springless Pressuretrol as a backup, and another, unmodified Pressuretrol as a backup to that. (The latter provides the required complete shutdown for the gas millivolt system.)

ethicalpaul

Thanks—I will try to spin the tiny allen screw. It does look currently set to the low range so we’ll see. Everything you said makes sense to me. A completely loose spring == no spring