Pressure too High

MikeinNEPA

I'm very new to steam systems in general and just got Dan's "Lost Art" book. My Pressuretol is set as low as possible but the system reads that it is outputting between 3 and 5 psig, which I know is way to high for a residential 2 story single pipe with a dry return. I have 2 questions. First-  I have one pipe with a bad water hammer, I have replaced every air vent including the main, checked the pitch and added insulation all with no change, the water hammer is at the start of the cycle. Could the high pressure cause this? Also the boiler is short cycling because of the pressure and the water hammer only happens one the first cycle. Also this weekend I'll be adding another radiator, in the hopes of reducing the pressure (as well as adding some heat to a colder part of the home.) If that is not enough of a pressure drop my second question is, as I'm limited on floor space for any more radiators could I install open element base board ( say 10') under the floor between the rafters. My goal with that is really 2 fold one I believe it would warm up my basement a bit ( its gotten colder as I've insulated the steam pipes.) and 2 I'm hoping it would warm up the tile floor in the galley kitchen. Any thoughts would be really helpful. Thanks.

nicholas bonham-carter

yet more pressuretrol problems!

that high pressure will prevent the vents from working properly at best, and at worst will make them into paperweights.

when you get a new pressure control [consider a vaporstat], hopefully every vent will work as it should, however you may still need more main venting.

the below floor heating can probably be done with a separate hot water loop from the boiler into pex tubing, and plates between the joists.

post a picture here of your above boiler piping and some faulty piping may be seen.--nbc

Rod

Lower the Pressure

Hi Mike-

   You need to get the pressure lowered before the high pressure trashes your new vents.  What model Pressuretrol do you have?  It sounds like you may need a new pressuretrol. Rather than just replacing the  pressuretrol you might want to consider a vaporstat as they are more accurate at low pressure. Adding radiators isn't going to change the pressure situation.

Heating the basement - You maybe better off using a hot water radiator to heat the basement. This can be run off the steam boiler. `Setting up a stream radiator in the basement can be a bit tricky.

Water hammer- Check that your radiator valves are fully open. Also check

for any sags in the piping or fittings that could collect and "pool"

water. You might want to post some pictures of your boiler as perhaps we could see something that could be causing the water hammer.

- Rod

MikeinNEPA

reply:

The vents seem to be working fine ( slight hiss that stops as the steam builds up and the radiator gets hot) They are a more expensive vent, I don't remeber of hand it was $18 each came in a red and black box its adjustable and feels solid like its all brass.

With reguard to the under floor hear do you mean running a hotwater line  to the element, or use pex to create a wet seal for the return ( I know in Lost Art they show a system like that.) that would rouble abck to the runoff?

MikeinNEPA

Lower the Pruessure

I'll take some pictures and get the pressuretrol model info tonight and post them later tonight. I did check the valves they are all wide open, and the pitch from the radiator to the main is good ( its about a 25' runoff.) My logic on adding the radiators was that it seems the boiler is oversized for the 5 radiators there, there is currently 3 plugged runoffs to the systems from the previous home owners.  I have not thought about it bring the pressurtol though.

nicholas bonham-carter

expensive vents

gorton #2's are about 2 1/2 times that price, but when you consider the alternative is to pay the gas company to force the air out, the price can be put in perspective [i have 18 of them!].--nbc 

MikeinNEPA

Gortons air vents

I actually replaced some of them they only say gortons "1965" on the, they are round right angle vents. Would they be worth trying to salvage?

BobC

Gauge

It is possible that your pressure gauge is not working right. i have the stock 0-30PSI gauge on the front of my boiler as well as an auxiliary 0-3PSI gauge that is mounted beside the vapor-stat.



When the boiler turns off because the cutout of the Vapor-stat is reached, the 3PSI gauge reads 0.75PSI (the set-point of the vaporstat) while the 30PSI reads almost 4PSI (that 30PSI gauge reads just a bit above zero when the boiler is cold).



Those 30 PSI gauges are known to be unreliable at the low end of the scale, the only way to know is to have a low pressure gauge along with the required 0-30 gauge.



Does the gauge glass water bounce up and down a lot when the boiler is making steam? Does the water in the gauge glass look dirty?  If so the boiler might have to be skimmed.



Check the near boiler piping against your install manual and post some pictures so we can see what you are dealing with.



Bob

MikeinNEPA

gauge

I'll get the pictures up in a an hour or 2 when I get home, the gauge could be wrong it does not jump much but it always shows between 3lbs ( even when the burner is off) and 5lbs. The gauge looks clean however there is some condensation inside of the glass. I'd must rather replace that that the pressurtol given in the price difference.

Jamie Hall

If that gauge

is reading 3 pounds with the system off, it's not telling you much about what's really going on.  With the system off and cool, the pressure in the boiler is going to be 0.  Chances are the gauge is not that accurate -- 30 pound gauges aren't.  However, you have to have one; it's a code requirement.  What you can do, though, is add a nice 0 to 3psi gauge on beside the one you have -- there are any number of different ways to pipe that, and I don't know how yours is set up, but there's sure to be some combination of Ts, nipples and elbows which will work!



Be sure when you add radiators that you are still within the EDR rating of your boiler -- other than that it's an easy way to get more heat, and not that hard to do!

Jean-David Beyer

Why 30# gauge on boiler?

I know the code requires a pressure gauge that reads to double the pressure of the relief valve. I learned that from my steam locomotive friends who often have 350 PSI gauges on their boilers. I always thought that was to provide a margin of safety so that the bourdon tube inside the gauge would not fatigue and break. Breaking would be a disaster in a steam locomotive because it would probably kill anyone near.



Now with a lower pressure boiler, such as one with a 15 PSI relief valve, it might be that the the gauge assembly is strong enough to contain the steam without breaking the gauge. But maybe not.



But if this is the true reason for using a high pressure gauge, it would be unsafe to have a 3 PSI gauge on there. In that case, it would make sense to have a 1.5 PSI relief valve on the boiler instead of the 15 PSI gauge usually used. I do not know if anyone makes such a thing.



Something is probably wrong with my reasoning here. Can an expert point out what that is?

jpf321

what is the temp differential between cycles?

how far does your thermostat go down before the cycle starts? for example .. you could have it set for 70degF but you might have a 3deg swing that would cause the temp to drop to 67 before firing ..



water hammer at beginning of cycle is often caused by too much condensate all at once assuming you have checked pitch and everything is insulated.



you may also have your rads vented too quickly .. steam hitting all that cold iron too fast will create a larger than desired amount of condensate ..



1) try slowing your vents a bit on the rads or areas that seem to have the worst hammer. and 2) try to decrease the temp differential between cycles(or programs 62day vs 70 evening similarly 62night vs70 morning .. i'm an advocate of leaving the temperature constant ALWAYS 70.) ..



my swing is 0.5deg .. it's the smallest available to me with my thermostat .. if you tell us the brand/model of your t-stat perhaps we can find the manual for it.



does the banging happen during the day? in the middle of the night? early morning? or early evening? or on EVERY CYCLE?



thanks.

Brian_74

Why 15# relief valve

At first I thought the 30# gauge was a hold over from the olde days, but according to TLAOSH, residential steam went from 60 psi to 2 psi pretty quickly. I guess folks realized that not blowing up was good for business (see pp. 15-16).



So I figure that either the 30# is related to the 15# and we just need to know why it's 15#, or there's something about 30# gauges that makes them cheaper or more durable than 25# gauges, or it's a historical accident. Maybe some old timer just used an auto tire pressure gauge and that's what started it, but I'm pretty sure the old cars ran at 50-60psi tire pressure.



Sorry. I eliminated a possibility or two but don't have an answer.

Jamie Hall

An historical accident...

The fundamental code requirement is that there be at least one pressure gauge on any boiler capable of reading to at least twice the pressure of the highest pressure relief valve (usually, with us residential folks, there's just one relief valve!).  So the question is, why are residential relief valves set at 15 psi and not some other pressure?  That's the historical accident: long ago when boiler codes were being written, for some reason which is obscure to me a whole different set of code requirements were written for low pressure boilers and high pressure boilers, with the break being at 15 psi.  I honestly don't know why 15 psi was chosen -- maybe someone else on here does -- but it was.  So our residential and many commercial boilers are rated at 15 psi, and use the low pressure code requirements (a lot less complex and expensive).  So their relief valves are set for 15 psi... so our pressure gauges are set for 30 psi...



Most pressure gauge bourdons are good for a lot more pressure than the gauge itself is rated for.  It will usually say in the gauge specifications at what point they will straighten out too much...

Jean-David Beyer

pressure gauge bourdons

"Most pressure gauge bourdons are good for a lot more pressure than the gauge itself is rated for."



Maybe that is the difference between home heating boilers and the ones my friends have to use in steam locomotive boilers. There, the usual operating pressure was about 225 PSI, although some went as high as 275 PSI. So their pressure gauges went twice as high. At some point I imagine it is not really possible to have a strong enough bourdon tube, but I am glad it is not my problem. You sure would not want boiler pressure steam released into the cab of your locomotive. Talking around 400F at those pressures. And the steam does not stop until all the water in the boiler has evaporated or the boiler cooled down below the boiling point. I saw someone blowing down a boiler of a small locomotive (175 PSI). Without thinking, I assumed scalding water would come out of the pipe. But it flashed to steam before it ever came out of the pipe. It would probably boil the meat off the bones if anyone got in the way.



I imagine the pressures and temperatures in a steam powered power plant are much higher. I wonder if they use pressure gauges, or if they put strain gauges on the steel components.

MikeinNEPA

Model numbers.

Ok sorry I can't post picture turns out my home Internet is down and they can't come out to fix the time until later today, but that's another story. So the t-stat is a Honeywell rth2310b from Lowe's. It seems to start the boiler in about 3 deg intervals so if its set to 70F it will kick off at 67F, I don't know this for certain but that is what I have observed in passing. The unit it self is a Pennsylvania Furnace with no model number on it but it says 15psi max with 150K BTU .120K BTU on the tag. The boiler is a ITT McDonnell and Miller with the number 205195 on it, that seems fairly new compared to the furnace it self. and the pressurtol is a Honeywell VA404A ( this number was ink stamped on the side of the unit) it looks to be about as old as the whole unit it self. I will had the new radiator tomorrow and if they have the items in stock at my local plumbing store I'll put on another gauge as well.

Oak Park Electric

Whats with the 30?

Furnaces are frowned upon here.  You, fortunately, have a boiler. 



Jamie already said it  well, but I guess I'll throw this in anyway.  It's from a different thread, but same subject.  Residential boilers tend to be rated at 30 or 50 PSI for hot water, and 15 PSI for steam.  The reason is that 15 pounds is the breakover point between "low "and "high" pressure for steam systems.  Somehow it was determined that 15 PSI was pretty safe as a maximum for unattended use.  High pressure steam systems are dangerous and in this area they require a licensed engineer (stationary) to be present when the system is operating.  Plumbing / heating / mechanical codes want one gauge on the unit that has a range of twice the relief valve pressure.  Not  "you must have a 30 PSI gauge", but instead  "you must have a gauge with a scale that is double the relief rating ".  So the boiler is rated 15, and consequently so is the relief valve.  Do the math.  That is why we have 30 pound gauges.  You do not have to worry about the tube in the 3 PSI gauge failing at 15, it won't.  Maybe at significantly higher pressures, but those would blow the boiler up before the gauge. Conventional power plants operate at around 2200 PSI and 1050 degrees at the high pressure turbines.  Primary Cooling Loops (high pressure hot water) in pressurized water reactors run about 2350 PSI.  They both use electric pressure transducers that send a signal to a remote readout in the control room. There are also  "regular" looking gauges used in hydraulic systems that go to 10,000 PSI and they use Bourdon tubes.  It's just that the tubes are made out of phosphor bronze or monel.

MikeinNEPA

Problem solved.

So this weekend I installed the new radiator ( it required more carpentry that pluming work but that's another story.) I found a few things one the Gauge is very wrong, I set the boiler to pilot and opened the plus I had in the main and it still ready 3psi, so if my math is correct when its running and it shows a hair under 5psi, its really a bit under 2 psi. Also on a good note I no longer have a water hammer in the run going to the radiator in the front of my house. So all and all everything works great. Thanks every one for the help. This forum is a great resource.

BobC

0-3PSI gauge?

I'm glad to hear your system is now working quietly.



the 0-30 PSI gauges are not very useful when it comes to seeing what pressure a steam boiler is operating at. You might consider adding an auxiliary 0-3PSi gauge so you can see exactly where you are.



Bob

MikeinNEPA

0-3 psi

any recomendations on a brand of gauge, and where in the system should i put it in the system.