Pressuretrol--dont quite understand

btc

Even though I have read Lost Art numerous times, still dont understand how setting on Pressuretrol affects basic operation of boiler. How does lower Pressuretrol setting vs high matter? Boiler has two states--flame on and flame off. In theory, as long as vents are working, air being released from system, radiators heating evenly, etc., shouldnt you want boiler to shut off only upon reaching temperature? Sorry for the elementary question, but this continues to baffle me...

I do understand Ptrol role as a safety device, and maybe that is its primary purpose. Just confused about Pressuretrol as system/comfort optimizing device during normal heating cycles...Thanks Brian

Dana

The pressuretrol cycles the boiler on and off as it is making steam. Pressure in a residential steam boiler should never build more than 2 psi, if it does the system won't heat the radiators. As long as your thermostat is telling the boiler it needs heat, the boiler simply cycles on and off by steam pressure and continues to heat the radiators. It does the same job as an aquastat on a hot water system, it simply controls the boiler by reading pressure rather than temperature.

DanHolohan

For the air vents to reopen

after the initial firing cycle, the system pressure has to drop below a certain point. That's the pressuretrol's main job - to make the air vents work.

Steven Todd

how long off?

Assuming the thermostat's target temperture is not yet reached, and the pressuretrol turns the boiler off (because 1.5lbs of pressure was made), how long typically should the boiler stay off? (And if it comes back on 'too soon', what might be the cause?) Thank you.

David Efflandt

high pressure less efficient

Besides the air vents not opening at higher pressure (which leaves air instead of steam in radiators), it takes more energy to raise the pressure, and higher pressure steam is more dense, so it moves and changes direction slower.

Heat transferred to the radiator is due to steam condensing to water. But at a higher pressure, the boiling point of water is higher, so the condensate will be hotter and the net effect is about the same heat transfer (or less if air does not vent).

So raising the pressure above design pressure just raises your fuel bill without any heat gain, or maybe even less heat if high pressure keeps your air vents closed.

btc

Dan, thanks. As usual, you get to crux of things. Occasionally, one of my hoffman 1a vents doesnt open at end of cycle when heat goes to end of rad, which then causes that rad to not heat next cycle. Any advice on how I can test to make sure my Pressuretrol doesnt need replacing? It is an old Honeywell PA404A with an additive scale. Thanks. brian

DanHolohan

For one-pipe,

just set the cut-in to .5 psi and the differential wheel to 1 psi. If the system pressure if all over the place then I'd think about replacing the pressuretrol.

Fred P

does it make a difference

if you cut out at 1.5 or 2??

Patrick Powers

Quick question. I have always wondered. If the pressuretrol is normally closed open on rise. How is it that when the pigtail is plugged the pressuretrol shuts off? If the pigtail is plugged how does it build up pressure? Just curious?

DanHolohan

Generally,

the lower the better. Saves fuel dollars.

DanHolohan

Good

question. I've often wondered about that myself. I figure the pressure bleeds in though the clog and gets stuck there.

jim_14

what exactly does it mean to cut in at .5

or 1 or 5 lbs?

Doesnt the boiler at first start up have 0 pressure? Can you explain what exactly the cutting in means??

Mark Hunt

The boiler


will fire when there is a cal for heat and the pressure is at or below .5. The differential on the standard pressure-trol is the "cut-out" and is added to the "cut-in" pressure.

So if you have the "Cut-in" at .5 and the differential at 1, the burner will "cut-out" at 1.5 and cut back in at .5 as long as there is still a call for heat.

Hope that helped!

Mark H

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jim_14

Yes I get it now,

thats a good explaination!!

So if someone had a cut in of 4 lbs and a differential at 1 lb the boiler would kick back on at 4lbs and cut out at 5 lbs.

So keeping the pressure at 4 lbs is actually wasting $$$ and compressing steam? and Im guessing it would cause some makes of air vents not to re-open??

(this is not my case, I am at .5 cut in )

Mark Hunt

You got it!


Yup.

That's it exactly.

If you read Dan Holohan's book "The Lost Art Of Steam Heating", you will find that the industry settled on a "2psi" maximum for steam heating systems in residential applications.

Before that, the sky was the limit and sometimes those higher pressure systems flew through the sky!

The "pressure-trol" that comes as standard equipment with steam boilers today is not really the best choice for controoling most steam boilers. Believe it or not, your system will operate more efficiently on OUNCES of pressure instead of pounds.

Most steam boilers are sent through with 30psi gauges today. You would probably NEVER see any movement of the gauge. That is because the gauge can't register the lower pressure that the boiler is actually operating at.

We remove the standard "pressure-trol" and replace it with a "vapor-stat". We also replace the 30psi gauge with a 5psi gauge, (even that is bigger than we need).

I LOVE doing this!!!!!!!!!!!!!

Mark H



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jim_14

Its been a while since Ive read

the lost art. BTW my pressure guage does move, when it hits 2lbs exactly it shuts off.

Thad English

Redundancy?

Can anyone think of a reason to have 2 pressurtols on a steam boiler? Specifically, a standard Honeywell additive one on a pigtail and another "subtractive" pressurtrol mounted along side the pressure gauge. I have read "We Got Steam Heat" and started "The Lost Art" last night, but can't find any instance of having 2 pressurtols (nor can I figure out why you would have 2). On my Peerless steam boiler, though, there are 2 of 'em. They both appear to be wired, but the Honeywell 'additive' is the one that is controlling the system. The system is running fine with the 2, I just think it is weird. Any thoughts?

DanHolohan

Required

on commercial boilers, and on boilers serving multi-family housing. You set the second at a higher pressure than the first. It's there to shut off the burner should anything go wrong with the main pressuretrol. This is supposed to keep the relief valve from popping (a character-building experience). Each pressuretrol needs to be on its own pigtail.

Dave DeFord

Do you replace the 30# gauge...

or add a 5# gauge. On a post a couple of weeks ago I questioned the need for a 30# gauge and Noel told me that it was code to have a gauge that reads 2x the maximum pressure of the boiler. Due to that I was going to add a 2nd 0-5# gauge to my boiler next summer when I do some other upgrades. Just trying to find out whats up so I don't do anything stupid or waste money.

Thad English

And that makes sense on the semi-commercial boiler I have in this house (384,000btu/h). I'll add putting the 2nd pressurtrol on a pigtail to my growing list of adjustments that should be made to this system.

-Thad

Patrick Powers

question

That makes sense.

DaveF

My pressuretrol is set at 0.5...

but it acts like it is set at 3. The 30# gage shows 4 psi when it cuts out and 3 when it cuts in. I have a 1995 Dunkirk with a Honeywell 404 pressuretrol.

Is there any maintenance (cloged pigtail) that should be performed? Should it last longer than 9 years?

Tom_42

My system never

cuts out until it has reached thermostat temperature. I think this is a problem for me. This morning my boiler ran for over two hours and only rasied the tempature in my living room 3 degrees. I wonder if there was too much pressure blocking the steam from the radiators? I also have a 30psi pressure guage and the darn thing never moves.

scrook_2

bad vent

on the radiator in the LR (does it get hot all the way across fairly quickly?) and/or bad (leaking steam) main vent(s), or a steam leak elsewhere, including inside the boiler itself?

Tom_42

overfilled boiler

I don't think the problem is the vent in the LR. A couple of days ago the water line in the glass guage was really high. After using the blow down to flush the system a couple of times the level dropped to the middle again and I got good hear throughout the house. However that was short lived and my system is at it again except this time the water level is in the middle of the glass. I have no idea what is wrong now.

David Albert

My pressure gauge sometimes reaches 5psi, why?

My cut-in is set at 0.5, with diff set to just over 1 on the dial. But the cut-out doesn't seem to happen until the psi gauge reaches 5psi, which has been happening lately in the very cold weather. Can this be normal, and if not which part is most likely at fault?