Steam boiler pressure gauge

STEVE PAUL_3

No, I am not the Steve Paul that works at Princeton. The only connections that I have with less than 6- degrees of seperation from Princeton are:
1- My Brother graduated from Princeton
2- My son-inlaw worked at PPL
3- My company services the Princeton area

ALMOST THE SAME THING!!!

Howie_7

Steam boiler pressure gauge

Can someone explain the purpose of the pressure gauge and pressure control on a steam boiler, ie. which pressure is it gauging (internal or output), how it affects the boiler, how to tell is it's working, etc. Right now the control is set below .5 psi and the pressure can go as high as 10 psi w/o anything happening. Is this normal?

Brad White_203

ASME

requires a gauge with a scale of twice the boiler's rated pressure. For low pressure steam, this is 15 PSIG maximum so a 0-30 PSIG gauge is used, sometimes a compound gauge -30"Hg to +30 PSIG.

There is nothing in the ASME boiler code that says such gauges must be useful...

To run at low pressures (as you seem to be doing, at least at the low end), a gauge of 0-5 PSIG, 0-3 PSIG or 0-32 ounces (2 PSIG) are far more useful.

If you are going to 10 PSI from 0.5, I suspect that you have a plugged siphon (pigtail), so get that attended to pronto. The control is partially blind to what is happening in the boiler. Not a safe nor sane operating condition, even if you have a relief valve. (Does THAT work?)

The gauge is just instrumentation, telling you at what pressure the boiler is operating. It does not "control" anything. All gauges, as with all steam controls, should be separated/isolated from the steam by a pigtail/siphon loop.

I specify such piping to be red brass to minimize blockage. Steel tubing can collect stuff or make it itself.

nicholas bonham-carter

abnormal high pressure

your pressure is going too high. the pressuretrol [or vaporstat] will keep the boiler pressure from rising higher than the set-point [best to be under 1 psi].i would say that your pressuretrol is not working because of internal malfunction, or because the curved pipe [called syphon, or "pigtail"] it is mounted on is blocked.

if you need a new one consider getting a vaporstat for greater control of the low pressures at which steam moves more quickly.

for more on this subject and much more steam info, get a copy of the lost art of steam heating on this site.you'll be glad you did.--nbc

Howie_7

Thank you Brad and Nicholas for your feedback.

Being that this is a BRAND NEW boiler (installed in Oct '08), I would think everything is running fine. I did have the installer come back once because of this same issue, and they just installed a higher limit relief valve (15psi to 30psi). They did tell me this...that the gauge tells me the pressure inside the boiler, and the control is linked to the output pressure. True?

All in all, I don't think they resolved the issue, and that's why I'm here. I'm hoping this would be a easy fix.

STEVE PAUL_3

Boiler gauge

Pressure issues aside, I would seriously reccomend finding another contractor for service. The maximum setting of a pressure relief valve for your boiler should not exceed 15PSI. A 30 PSI relief valve is for a water boiler. This was not the proper fix.

Brad White_203

I agree with Steve

installing a higher pressure relief valve is not only against code, but is not safe and may jeopardize an insurance claim even if it is not involved in a mis-hap. Any excuse and all that. He should know better.

That said, the gauge just tells you what is going on inside the boiler (as far as pressure is concerned). The pressuretrol (or vaporstat, a lower-scale pressure control which I doubt you have), determines what the minimum (cut-in) and maximum (cut-out) pressures will be.

These too should be installed in brass pigtails and the gauges ideally off of their own pigtails.

Howie_7

Steam boiler pressure gauge

David Nadle

Steve?

I knew a guy named Steve Paul who worked at Princeton. Is that you?

alang

I work with a Steve Paul at Princeton

He's a physicist at PPPL (Princeton Plasma Physics Laboratory). Are we talking about the same Steve Paul?

Steve R.

David Nadle

Yes!

I was at CUPPPL. Now if the Steve Paul on this thread turns out to be our Steve Paul, that would be something...

Phil_17

Brand new...

Just because it's brand new does not mean the pigtail cannot be blocked. The installation will leave a lot of oily gunk and other debris in the boiler water, and that can get into a pigtail, gauge or pressurtrol and gum things up. If the boiler is new and hasn't been skimmed then it's quite likely that there is gunk in there.

To directly address your question, the pressurtrol (or vaporstat) should be measuring the same pressure that the gauge is measuring. It's the static pressure in the boiler. Dynamic pressures exist all throughout the piping, and while there is lot's of interesting stuff to be observed there we don't typically monitor any of them.

-Phil

Howie_7

Pressuretrol

Brad, will the pressuretrol turn off the boiler if it reaches the maximum set pressure?

Phil_17

Yes

It is also possible that being a brand new installation the pressuretrol is not wired correctly... It certainly should turn off the boiler when it reaches the set point.

Howie_7

TY PhilC...

Unknown

Rather scary when a guy who's supposed to know what he's doing says it just needs a higher pressure relief valve. Sort of like a electrician fixing a blow fuse by putting in one with a higher amp rating when he should be correcting what is wrong. While overloaded wire can cause burn down your house, at least it doesn't blow it up!
I think you need to find yourself another heating contractor ASAP!!!

Erich_3

More Information Needed

Howie, you need to tell us the exact model of your boiler and post pictures of the near boiler piping. Do you have a copy of the installation manual? Most installation manuals are available online or you can call the manufacturer and have them send you a copy. You need to have the installer reinstall the correct gauge. From your description of the problem with the gauge it is probably safe to assume that there are other deficiencies in your system. Did the installer use black pipe or copper lines when he installed the boiler?

Unknown

Erich- You made a good point on the possibilities of other deficiencies. Very likely.

mike m_3

Pigtail/Siphon ?

I always wondered what the relationship was between the pigtail, the LWCO and the pressuretrol. Does the pressure trol act on a vacum or suction, or is it pressure? What is happening for instance, inside that pigtail during the on portion of the cycle?

nicholas bonham-carter

pigtail

the boiler, when on, has water boiling inside which, if it continued to boil without interuption, would develop a very high pressure.

the purpose of the pressuretrol is to interrupt the command signal to the burner, when a certain pre-set pressure is obtained [ideally 12 ounces in a steam system].

the purpose of the pigtail is to keep a small water-seal between the pressuretrol and the steam rising out of the boiler.

you would find "the lost art of steam heating", available here, very informative, if you are lucky enough to have a steam system.--nbc

mike m_3

Pigtail/Siphom

Thanks for that answer nbc. I am fortunate enough to have one pipe steam in my house and thanks to numerous Wallies and my own copy of 'Lost Art', this system seems to be running quite well.I am still expirementing with radiator vents however,and recently replaced the totally plugged pigtail. Thats when I began to wonder if it(pigtail) sees pressure always or is ther sometimes a suction fuction. In other words is the pressurtrol pushed or pulled?

nicholas bonham-carter

push-pull?

at the end of steaming, when the burner is shut off, the steam condenses quite quickly leaving a vacuum , which can be quite strong. the main vents have to let air back in to relieve this situation [a tough job but something has to do it] . the water-seal in the pigtail will not be pulled out because the p-trol, gauge, etc. are not open to the atmosphere. food preparation facilities use this steaming method to vacuum-seal cans of food.--nbc

David Nadle

both, but mostly push

The pigtail has a slug of water sitting in the bottom of the coil which isolates the hot steam on one side from trapped air on the other side, so your gauge and p-trol are protected from high temperatures. The pressure will be the same on either side of the water.

When the pigtail gets clogged up the p-trol and gauge will not sense the correct pressure. The boiler may run too long and develop pressure your radiator vents can't cope with. If you have loud hissing vents late in the cycle with clanging, spitting, etc., check your pigtail.