Pressure

crash2009

I have read quite a few posts on the subject of pressure.  None of them seem to address the question I have.  I know that low pressure is a good thing, but it appears that I don't have any.  I just put on a brand new Wika 0-3 and the needle does not move.  There are 2, 75 foot mains with a Hoffman 75, Gorton 1, and a Gorton 2, on each side.  I can hear the Hoffmans both clink.  The Gortons get hot and cool down (so I think they are working) There is about 435 sq ft of radiation connected. 

To test the gauges, I shut off the boiler, closed the return valve, and the supply valves, to force some pressure, and the gauge needle, pretty much immediatley, shot up to .5 lbs, so I know the gauge is good.



Is this normal for the boiler to shut down on thermostat satisfied, before building any measurable pressure on a 0-3 ?  Is this what you call short cycling? 

Jamie Hall

In answer to your question,

in one word: yes.  And no. 



Yes, it is quite normal for a steam system to satisfy the thermostat -- on warmer days! -- without building up any noticeable pressure (OK, OK, if you had a super sensitive manometer... but that's not what we are talking about).  Consider that the design shutoff pressure of a Hoffman Equipped system, for example, is 9.5 ounces per square inch -- that's the shutoff.  You will only reach that on a really cold day, or when recovering from a deepish setback (and in fact, on an ideally balanced system (yeah, right) you might not even quite reach it then).  So not to worry.



And that is not short cycling -- short cycling occurs when the boiler is making steam a good bit faster than the radiators can condense it, and so has to turn on and off (could be for as little as a minute on, 20 seconds off!) to compensate.

Steve_210

i have

never been able to build any pressure on a 3lb guage without turning the stat way up. 88-90

crash2009

Cold weather simulation test

I did an air-exchange by using the exaust fan in one of the kitchens.  I was trying to convince the boiler, that it needed to make more pressure, so I could see the gauge move.  The boiler ran without stopping for 45 minutes.  The radiators that I could get to were 60-70% hot across, but the gauge still did not move. 

Am I correct in assuming that we don't build 0-3, measurable pressure until all the rads are completely full and the rad vents are fully closed? 

And if the thermostat is satisfied before that I may never see that gauge move.  How am I to answer the question "What pressure are you running?" if I am unable to read the gauge.  Do I need a gauge that reads ounces?

Jamie Hall

Sounds like

your boiler is pretty nicely matched to your radiation -- be happy!  And no, the gauge won't move until the radiators -- all of them -- are really full and their traps (assuming that they have them) (or vents, on one pipe steam) are closed.  Until then, all you are going to see is the head loss of the steam and air moving in the pipes -- and that's minimal.



How do you answer the question of what pressure do you run on?  Well... actually, you can try saying something like "an ounce or so" and be perfectly correct.  What folks usually bang on about around here is where their system's vapourstat or pressuretrol is set to trip.  Which is a little artificial since unless you really provoke your system (I like the turn it up to 88 idea!) you don't get to that radiators all full stage until very late in a cycle, if ever.  But you don't really want to, either -- as I noted earlier, the ideal system is one in which the boiler can produce exactly the steam the radiators can condense, and no more.  But we usually oversize from that a little -- partly for the "pickup" factor (the steam required to heat up the pipes themselves) and partly a safety factor.  You will notice, by the way, if you ever do get to the radiators full point, that the gauge will start to move rather abruptly -- and move remarkably quickly.  Kind of fascinating.



On a slightly more theoretical note, going back to that "minimal" pressure above -- it actually isn't minimal; in a typical vapour system, for instance, it is probably around a half pound differential between any given cold radiator and the boiler.  But... that cold radiator will actually be at a very slight vacuum, so the pressure at the boiler will be that vacuum, plus the 8 ounces or so of pressure drop in the pipes -- and probably works out to just about atmospheric by the time you're all done.  Maybe three or four ounces.  On the vapour system I have observed the most, it is just barely enough to get the vapourstat to quiver, never mind come close to tripping over.

crash2009

Thanks

for explaining all that Jamie.  I led myself to believe that a pressure controller could be set to maximise heat and minimise fuel use.  The way you explain it, it is just a high limit device that shuts down the burner if the set limit is reached.  The gauge is just there to confirm that the controller is doing what it is set for. 

So now I know that my gauge is working and what it is for.  I want to test my pressuretrol next to see if it is going to work if I ever need it.  Also a lot of people tell me I should get a vaporstat.  I can justify a vaporstat if the pressuretrol is not working.  Would the test be as simple as closing the supply and return valves, let the pressure build to just past the pressuretrol setpoint, and if the pressuretrol is working, the burner should shut off.  If the pressure continues to rise past the set point then the pressuretrol is no good.

jpf321

yes and no...

pressuretrols (p-trols) are notoriously flaky (poor resolution) at low pressures 1,3,5psi .. so you can certainly try the test, but don't be surprised if it doesn't trip exactly where you set it. (same is true by the way with a vaporstat, but at least there you are quibbling over accuracy in oz not psi)



ok so where you get your fuel savings .. as jamie said, on low delta-t days (warmish), your t-stat will satisfy before p-trol .. however, on a high delta-t day (cold) you are losing heat faster, but your radiators are full and it is wasteful to try to fill them anymore but your t-stat is still not satisfied because you are losing heat at a faster rate (high delta-t). this is where the pressure come in .. once you fill your rads with steam (they are hot all across, and your vents are closed) there is no reason to JAM (high-pressure) them with any more steam. SO you want to shut off the burner (stop fuel consumption) as soon as you can detect (through a change in pressure) that the rads are full and not ready to accept anymore steam at the moment. if you can reliably detect "fullness" at say, 6oz, that's a much sooner (less consumed fuel) than if your best ability to detect fullness is 2.5PSI (40oz). the consumption difference between shutting down on pressure at 6oz vs. 40oz is your fuel savings.



OK so now we are shut down, what happens next, well the rads/pipes condense steam, pressure drops (mini vacuums in each area of condensation) vaporstat differential kicks in on pressure decline and the burner is started again .. this is where people have been asking about "I shut off on pressure but I kick in again 30seconds, 1min whatever later" .. well that time off is fuel saved, if you weren't shut down at that point (you were set at a higher pressure, then you would have been burning (consuming all that time) .. if you shut down 1min for example and you cycle 20 times (recovering from a deep setback; a different discussion altogether) then during that t-stat request you saved 20mins worth of consumption. you can then work your potential savings based on theoretical fuel consumption/minute. if you are firing oil @ 1GPH then 20mins would save you .33gal .. if you did that 30 times a month, you save 10gal at $2.75/gal = $30/month. A higher GPH a bigger savings.



not too mention greater potential stress on the vents if you JAM in at higher pressure as well as quiet enjoyment of near silent heating system due to low pressure (like mine is). I don't know about you but at the price of each Gorton #2, I want to stroke it gently with nice low pressure. Additionally, I want to feel my heat, I don't want it to announce itself by way of whisteling/hissing/spitting rads.



Lastly, cutoff at lower pressure will allow condensate to flow around the system more freely (draining from rads, running in counterflows, etc). I'm not sure if pressure substantially impacts water hammer, I think that's more due to steam velocity.



Anyway, that's my take. I'm sure there are a few other advantages to cutoff on lower pressure. Mine is set for 6oz. with a 2oz diff. My goal when I was trying to determine where to set it was this: 1) ensure that the furthest rad is able to heat all the way across, and 2) find the lowest pressure that will reliably and accurately trip the vaporstat.



BTW, my gauge is 0-20oz wilka http://is.gd/gvGDK.



Hope this helps.

crash2009

last winter

I remember a day last winter when we were piped with every mistake you could have.  The plumber asked me to shut it down at 5 am so he could do some work on it at noon.  He drained it, did some flushing, put on a new safety valve, filled it up, turned it on, and left.  About an hour later, I heard a whistling sound from downstairs.  I went upstairs to find out what the noise was.  There were 2 or 3 rad vents stuck open and the steam was taking the paint off the walls.  I wonder what pressure that was?  If I had taken a rad vent off, I am sure the steam would have shot out the hole for 2 or 3 feet.  There was so much pressure, I thought it was never going to shut off.  Thinking back on that, I think that was a very dangerous situation for someone as inexperienced as I to be in.  And that event was likely an indication that the pressuretrol is no good.  I have no idea how old it is.  I think I am going to save myself the hassle  of a dissapointing test and just replace it with a vaporstat.     

jpf321

you need both

for code you need both. as well as a 0-30 gauge

Jamie Hall

Wait, there's more!

As they say on the tube... some codes require two p-stats on bigger boilers -- like mine.  One at some nominal value, say 5 psi, and one, manual reset, at a bit below the safety valve.  Then I have a vapourstat (set at 9.5 oz at the moment).  Talk about belt and braces...



A minor word on vapourstats -- I have really improved the accuracy and precision of mine by putting a snubber in line with it.  Not only saves wear and tear on the 'stat, but also keeps it from bouncing off when it doesn't need to, due to minor pressure variations which are inevitable.  Thing cost relatively little... (in fact, the shipping cost more than the snubber!).

crash2009

code in Michigan

I'll phone someone tomorrow.  Cripes winter will be over before they make up their minds.  Might as well just follow NY. Where are you?

Jamie Hall

Connecticut

Code issues can drive you nuts, because they vary all over the place.  I have no idea what Michigan requires!  They probably don't either (that's a cynical remark, isn't it?).  Unless you have a pretty big boiler for a residence, though, I'm betting you can just have the regular p-stat and a vapourstat.  Good luck!

njsteve

pressure differentials

How long should the system take (very generally speaking, of course) to restart after high pressure cuts it off? obviously, it will depend on how quickly the steam is condensing in the radiators, but what is a normal range?



I am using a basic p-trol (and longing for a vaporstat) set to shut the boiler down at approx 2.5 psi and restart it at 1 psi. one of my new gorton #2's is not closing, even though all the rad vents and the other gorton 2 main vent are closed, so I know i'm losing significant pressure there. (btw, any thoughts on why that might be happening?)



right now it drops from 2.5 to 1 psi in about 2 minutes, and the burner kicks on again. is this too short a cycle? i don't want to damage my boiler while I try to figure out why my vent isn't closing. assuming I replace the vent with something that works, what is a normal time for this 1.5 psi drop?



thank you all for this wonderful resource!

crash2009

I guess

every system is different Steve, But I would think it would take as long as it takes to drop down to your start setting which I think you said 1 psi, assuming that the thermostat is not satisfied.



There were some bad Gorton 2's going around last winter.  Sounds like yours is stuck closed (creating pressure)  not stuck open (no pressure) I don't know what to do about that other than starting a new thread such as "I think my Gorton is not working"  I did that last winter and the guys here gave me a few little tricks to try.  I ended up sending it back to where I bought it and they sent me a new one.



I wonder if you are having short cycling symptoms.

crash2009

Pressure Test

I finally did the pressure test today.  It was a little un-nerving but it went ok.  The first thing I did was shut off the breaker and the power switch on the boiler.  Then I disconnected the wires and removed the pressuretrol from the pigtail.  I wanted to see for myself how this thing works so I took a real good look inside.  Inside the threaded peice there was a bit of old greasy teflon, and the hole was filled with water so I blew it out with compressed air.  Inside the box it was pretty clean and well lubricated.  When I first tried to move the rocker, the switch wouldn't click so I loosened the top screw a bit to get it moving again.  The indicator still reads 0.5.   I was surprised to hear the sound of the click changed when I moved the dial from 1- 5.  I noticed a small set screw with threadlock on it.  The set screw looked like it could be adjusted to control how far the plunger comes up.  I put an electrical tester on the wire contacts set to continuity.  When I lifted the rocker, I lost continuity.  Cool, I got this thing figured out.  So, I installed it back on the pigtail and went upstairs and turned up the thermostat. 



Finally the pressure test.  Close return valve, otherwise the pressure will back the boiler water up the returns.  Close both king valves.  Turn on the breaker at the panel.  Flip the boiler switch and watch the gauges.  The 0-3 climbed slowly, I closed the gauge valve at near 3.  Then started watching the 0-30.  3 psi was readable and it continued to rise up to 4.5 psi, then the burner shut off.  Hmmm, I guess it works.  I hooked up the continuity tester again and there was no power through the contacts.  Leaving the continuity probes on the wire contacts, I released some pressure.  And the switch allowed the burner to come back on.  Done deal.  Pressuretrol shuts off burner at 4.5 psi.  I just thought of something,,,,What pressure does the pressuretrol allow the burner to come back on?



As a high limit safety device, I guess thats good enough.  Which way to the Vaporstat department?

crash2009

Bump

I must have posted this wrong a minute ago.  Lets see if this bumps it

Jamie Hall

Most pressuretrols...

have what is called an additive differential.  That is, there is the main setting, at which the switch will close (and the burner come on) and there is a differential setting, which when added to the main setting gives the pressure that the switch will open at (and the burner shut off).



In most cases, it is possible to set the main setting at about half a pound, give or take (although it is none too accurate) and the differential at 1 pound -- which will give you a shutoff pressure of 1.5 psi which, for most steam systems (not vapour) is about right.  There are screws on the pressuretrol which adjust those settings (may have to take the cover off to get at the differential).



If you can get it down to that, and you have a moderately ordinary steam system, that should work; a vapourstat -- much as they are lovely gadgets -- may not really be needed (they aren't cheap).



But 4.5 psi is too much -- try to set it down.

crash2009

3.1

3.1 is as low as I can get.  Then back on at 2.5  The screw is hanging by about a half a thread.  Any way to trick-#$%^  this thing?

jpf321

remember the thread lock screw?

and also is your gauge good?

haaljo

My 3 pound guage flutters but no firm pressure.

I adjusted so it is slightly above 0 when cold.

Average the fluttering and figure about an oz?  Just ordered the 0-10 ounce: 

http://www.gaugestore.com/prodinfo.asp?number=33009

Cost $48 including shipping. My theory you can never have too many gauges.

haaljo

My 3 pound guage flutters but no firm pressure.

I adjusted so it is slightly above 0 when cold.

Average the fluttering and figure about an oz?  Just ordered the 0-10 ounce: 

http://www.gaugestore.com/prodinfo.asp?number=33009

Cost $48 including shipping. My theory you can never have too many gauges.

crash2009

Yes

I'll dig into that tomorrow.  Gauges were new.  The pigtail did get a little hot tonight.

haaljo

Crash - what's the point of installing a vaporstat...

if you don't see even an ounce on your 0-3# gauge? You haver proven your P-trol is performing it's safety function and that's all you want it to do. You got a vapor system (so to speak) and that seems to be what the Pro's recommend.

But it does drive me crazy that I can't see pressure. This thread (and kudo's esp to Jamie) is very informative.

crash2009

Haaljo

The point is that in this kind of weather, Nobody is going to see their pressure.  But in a month or two, I expect to see some gauge pressure while the boiler is working to keep these 6000 square feet warm.  If you re-read jpf's October 31 1:17am comments a pressure cutoff device is not only a high limit shutoff, but also a device that will reduce wear on your equiptment and also save you a couple bucks in fuel. It is easier to tinker with it now rather than in January when the boiler is busy.   

crash2009

Pressurized Eye Candy

Low, Medium, and High

http://www.youtube.com/watch?v=HSp7K_C6IDg

http://www.youtube.com/watch?v=l_CfD0h1LEE

http://www.youtube.com/watch?v=8lFDcgxy-WM

haaljo

6,000 square feet is 4 houses and

may be the ideal system to approach "vapour" operation during cold design day. In that case a vaporstat or ptrol functions almost completely as a safety device.

I don't know the specifics of your heating system but would be curious to hear what ya got in those four houses! and what your fuel consumption is.......

haaljo

Where do old p-trols go? See:

http://www.youtube.com/watch?v=6fGj0UdpHdU&NR=1

Found it when looking at crash thermal mixing videos. Don't throw the p-trol away when installing vaporstat - send it to tesla :-)

Charlie from wmass

Just playing bad guy for a moment.

Crash are you sure you boiler does not have a leak?

crash2009

Yes and No

The sight glass has an old leak at the bottom of the glass.  I just noticed yesterday, during the pressure test, a few drops came out of the skimmer.  I have to add about a half inch of water once in a while (I just started logging that) Back in June we flooded it and didnt see any leaks.  I have been watching the smoke stack everyday when I leave for work (no white smoke) Do you think its leaking somewhere I don't know about?

I just checked the log...I added half an inch on Nov 4.....It needs a half an inch today.

David Nadle

What part of the code?

I had a look at the 2006 International Mechanical Code. Here's the sum total of what it says about boiler pressure controls:

1006.7 Boiler safety devices. Boilers shall be equipped with controls and limit devices as required by the manufacturer's installation instructions and the conditions of the listing.

The Honeywell Vaporstat is a listed device, I think. It should be OK to replace a single pressuretrol with a single vaprostat in states that follow the IMC.

crash2009

Thats encouraging

David.  I think its ok too, unless told otherwise by an inspector.  I phoned one of the bigger supply houses the other day to find out what code we fall under here.  He looked it up in a code book for Ann Arbor Michigan.  As a residential building a single pressure limit device is sufficient, providing that it will cut out at (I forget) around 4.  So I think I could put up the argument that it cuts out lower than what they ask for.  Commercial though is another matter.  For commercial they require 2 cutout devices, 1 to cut out at around 4 and a lock out/manual reset a bit higher.  So the vaporstat/lockout combo would pass here.  I am not sure how we are classified. 

haaljo

If I was replacing my p-trol with vaporstat, I'd consider

keeping the p-trol and running them in parrallel. Doesn't seem so hard to do. Keep them separe with separte curly que thingy the name escapes me. I have had my curly que clog and therefore been without safety device. Can't see any disadvantages and there will be pride of doing the job the best you can.

But I think your wasting your money on a vaporstat in your situation.

haaljo

"Do you think its leaking somewhere I don't know about?"

Your observations describe no leaks of any significance. Your just operating at very low pressure - almost vapour and if the heat is getting to where you want to go that's good.

6K sq, ft is a lot of area to heat. Your annual heating bill must be out-of-sight with oil. But the Chinese word for Danger is also Opportunity. Please post your experiences in the next few months and pictures are always good for the Pro's.

Curious minds want to know.

haaljo

"Do you think its leaking somewhere I don't know about?"

And maybe your burner O2 and CO readings are way off. Do you see a blue or a yellow flame?

haaljo

"Do you think its leaking somewhere I don't know about?"

And maybe your burner O2 and CO readings are way off. Do you see a blue or a yellow flame?

Alex265

Can the system behavior change

from installing a new chimney liner system for the boiler? My steam system used to operate in the 8 oz. range throughout the cycle, and immediately after the installation of a new liner the pressure never goes above 1.5 oz., so basically I now have the same picture as crash2009. What have happened?

crash2009

No pressure

That looks like four of us with no pressure.  Do we all have a leak?  Or should we just be happy to be building little or no pressure.  I suppose that as long as the thermostat is happy, and the gas bill is not outragous, Who cares?  

The only reason that I can think of, in my case, is that the manufacturer called for a 1.5" equalizer, and we used a 2".  Who knows, I don't. 

haaljo

If you ain't losing water then you don't have a leak

Great pictures. My 10oz gauge comes Tuesday. Hope I see some pressure. Right now, I'm seeing fluttering on my 3# gauge so it's probably less than an oz.

Those valves you have on the supply lines came in handy when you did the pressure testing you noted previously.

Natural gas is cheap - efficiency almost doesn't matter.

David Nadle

Test the gauge

It's not plausible that you are operating at less than one oz/in^2.



I suggest you test the pressure externally with a manometer. You can make one out of a barbed hose fitting and a length of clear tubing. Hang the open end of the tubing up by the ceiling and connect the fitted end to your boiler drain. Open the drain, note the resting water line then fire up the boiler. The water will rise 28" for each psi of pressure.



If the manometer shows pressure but the gauge does not, the first thing I'd suspect is a clogged pigtail. The second thing I'd suspect is a bad gauge. a 10 oz range is pretty small. The top end of the range should at least be greater than the range of your pressure control to avoid pinning the needle. 0-30 oz/in^2 is a good range if you have a 16 oz vaporstat.

jpf321

I heated all my rads today almost full across....

and never broke 2oz.

brian_44

Is my pressuretrol defective?

I noticed this season when heating in the AM after a 3 degree setback that my 0-30 pressure gauge reads at 5 PSI and the boiler does not cycle off.  The pressuretrol cutoff is a low as it can possible go and the differential is set to 1.  My old boiler used to shut down...maybe I should have kept the old one from my previous unit?

I can't imagine the pigtail is clogged...if so I would have no PSI reading on the gauge. Is it possible there is crud above the gauge but below the pressuretrol which is preventing the pressure to reach the unit causing it not to cutoff?

Confusing...