Relief Valve

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Old 11-06-09, 09:10 PM
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Relief Valve

I've had two licensed plumbers look at my series 2 burnham gas boiler. The pressure relief valve always leaks a good deal of water whenever it operates. One wasn't worried. The other wants to replace the relief valve and the fill. So far neither has convinced me they know what's going on, especially since, over the years, they've looked at the problem more than once. I don't know much about this, but when I started to look it up, I began to think the boiler was too small. The boiler serves a five story, maybe 5-6 thousand square foot building. When the boiler operates, the psi rises to 45-50. Well above the 30 psi it is set for. This is what causes the pressure relief valve to open. Can the feed valve simply be adjusted, or replaced? Or is the working pressure of this boiler simply too low to heat this building? Are either of the plumbers on the right track? Thanks so much.
 
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Old 11-07-09, 04:01 AM
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You need approx 26 psi on this system with cold water. Heat that water and the relief valve better open and perform projectile vomiting of water. Not the proper boiler as is for this job as it is rated with a 30 psi relief valve. You can get a kit from Burnham for a 50 psi relief valve and includes a new label stating that the boiler is now rated for the 50 psi relief valve. I would also check the expansion tank sizing and for a bypass pipe.
 
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Old 11-07-09, 05:55 AM
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check the expansion tank sizing
A little more on that...

If your static pressure when the boiler is cold has to be 26 PSI, and you convert the boiler to a 50 PSI relief, you don't want the pressure when HOT to be any more than 45 PSI (10% lower than the relief valve setting).

For this, you need to have large enough expansion tank(s) to control the pressure such that it will stay below 45 PSI when fully hot.

Size and condition of the expansion tank(s) is what controls the upper pressure limit.
 
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Old 11-12-09, 02:40 PM
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So if I understand correctly by changing the relief valve and expansion tank(which I did), I have changed the maximum psi operating capacity of the boiler from 30 to 50 psi. Or at the least, that my boiler can easily handle the excess pressure with the proper tank and relief valve.

So my expansion tank can now hold 14 gallons. Up from 6(and that was water logged). What should I now set the expansion tank for(and could you explain the reasons why) and what should I set the fill for. As you said, the static pressure is about 26-28 psi. 130 degrees will bring the gauge to about 35 psi. Once I blew 30 psi I shut it down out of concern but it seems you could be saying this is potentially the end of my pressure problems? Thanks again.
 
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Old 11-12-09, 04:11 PM
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The proper air charge on the expansion tank is to match it to the COLD FILL static pressure of the system. If your cold pressure it 26 PSI, that's what you need on the air side of the tank.

Here's the thing though... do NOT try to measure the pressure in the tank, OR add air to it if there is any pressure in the boiler. You will not get an accurate reading. The water side of the tank must be at ZERO in order to set the air charge.

Best thing would have been to charge the tank before installing it to the system, otherwise you need to drain ONLY ENOUGH water from the system to drop the pressure to ZERO, and then check/add air to the tank.
 
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Old 11-12-09, 04:21 PM
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OK, you wanted some whys, I see:

Why 26 PSI static fill?

For every foot that you try to push water up a pipe, you need 0.432 PSI. Guessing that the total height of the system from the boiler to the highest point in the heating system is around 50 feet, it follows that you need 50 X 0.432 = 21.6 PSI... this is JUST ENOUGH to get to the top, and you always want SOME pressure in the system, so always add 4-5 PSI to that figure. This should ensure that you are never at zero PSI at the top of the system... there will always be a bit of 'headroom'.

You can check that the static pressure is enough by going to the highest point and opening a bleeder valve. You should get a steady stream of water, with a bit of pressure behind it. If it just sorta 'piddles' out, or not at all, or even SUCKS air in, you need more pressure.

The reason to charge the tank to the same as the cold fill is so that the 'bladder' inside the tank is at 'neutral' position. In this way you have the maximum available space in the tank for expansion. It also reduces the stress on the bladder by not having to flex as far, increasing it's life.

If your pressure approaches 45 before the boiler hits high limit, you need to think about an even larger expansion tank. (or adding a second one)

What size tank did you fit?
 
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Old 11-12-09, 04:32 PM
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The size of the expansion tank is determined by how many gallons of water are in the entire system.

When water is heated, it expands, that much we know...

If you take water from room temp to about 180°F it will expand in volume by just under 4%. Therefore, if you had say 100 gallons in the system, your expansion tanks would need to ACCEPT 4 gallons of water when the system was fully heated. The ACCEPTANCE volume of the tank is not the same as the sheer size of the tank. If a tank can hold 10 gallons, does not mean that it will ACCEPT that same 10 gallons when used as an expansion tank. This is because there is already a volume of air in the tank, and even air will only compress just so much...

There's some good tutorial info in this brochure at the Amtrol website:

http://www.amtrol.com/pdf/extrolbrochure.pdf
 
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Old 11-12-09, 04:52 PM
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Holy cow. Thanks again. Another question.

So I replaced the relief valve with a 50 psi valve. I set the pressure on the expansion tank at 15 psi. The boiler is rated 30 psi. I will readjust the expansion tank. But is it safe to run the boiler under these circumstances. I've been searching for these answers for days, it ain't easy. And the plumbers dont seem to really get it. Just put a 50 psi valve on with a defective six gallon expansion tank and go from there. That bothered me. Thanks again.
 
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Old 11-12-09, 04:58 PM
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I thought rbeck said your boiler is rated for 50 PSI ? If it weren't, then fitting a 50 PSI relief would be a big no no...

As long as your boiler is rated for 50 PSI, and you have a 50 PSI relief valve fitted, and your expansion tank is large enough to handle the expansion, then yes, it is safe.

By the way, all my calculations are 'padded' to err on the lower pressure side... the actual expansion to 180 is less that I stated, but this give a safety factor by allowing a higher water temp...

What size expansion tank did you install?

By saying 14 gallon, I presume you put a size 90 tank on? That should do it... presuming you have less than 180 gallons of water in the system (and I'm pretty sure you do).
 
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Old 11-12-09, 05:26 PM
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Its not rated 50 psi. I think rbeck was saying if I enlarge the tank and change the relief valve I have effectively changed the rating of the boiler to 50 psi. I have no idea but that's also what the plumber did, two plumbs actually. But I wont run the system unless im sure this is right though, because it doesnt quite make sense.

The expansion tank is an hft 30v by Bell and Gosset. As to the total amount of gallons in the system im not sure. I have 13-14 large radiators. Two risers and two returns. Five story building. I thought that was more than 180 gallons.

I just ran the boiler and at 140 degress I was at about 30 psi. Which is good. Can I turn the heat down to 150 and run the bolier safely until I have this issue firmly resolved? Thanks.
 
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Old 11-12-09, 07:39 PM
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The series 2 is rated for a max working pressure of 50 psi but shipped with a 30 psi valve. Legally you cannot just change the relief valve you must also update the label. If an inspector looks at the boiler and the label states a 30 lb relief valve he will shut it down. The label must match the relief valve rating.
 
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Old 11-12-09, 07:53 PM
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Thanks Rbeck. Can you send me a link or something that confirms that rating. I just looked at the boiler and it obviously said mawp 30 psi. So I'd like to confirm just to be totally safe. Although I could call burnham in the morning too. Thanks again. Big help.
 
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Old 11-12-09, 07:55 PM
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rbeck, that label has to come from Burnham, correct? How to do that? Call them?

BTW becky, that 30V tank should work fine... has the same specs as the 90... that one is a floor mount model, correct?
 
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Old 11-12-09, 08:06 PM
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Correct, it is a floor mounted. Thanks.
 
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Old 11-13-09, 04:08 PM
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I'm anxious to hear what you hear from Burnham.

I'm making some assumptions here, but this is what I think: most boiler manufacturer's choose to have their boilers sold with an ASME stamp, an H Stamp for heating boilers. (I think boilers can be sold in the U.S. without an ASME stamp unless required by a state or locality - but many do require it.)

The ASME stamp seems to be required to be afixed permanently to the boiler. In my case, it is a metal nameplate rivited to the firedoor. The nameplate, besides displaying the ASME stamp also has the boiler design details - e.g., boiler serial number, 30 psi working pressure, etc., engraved on the nameplate.

If that's what a boiler's ASME nameplate says, then if somebody sends you a decal up-rating any of the design data, then I would say that is without the blessing of the ASME.

If the manufacturer now says it is good for 50 psi working pressure, that's worth quite a bit. But then the ASME stamp no longer applies, right? You'd be running a non-ASME boiler, right? If the original pressure design was 50 psi, why didn't the original nameplate indicate that?

I don't think the relief valve setpoint is all that relevant. Why not set it for 100 psi or 1000 psi? My boiler's nameplate says the working pressure is 15 psi for steam and 30 psi water. Obviously, different relief valves would be needed for water or steam, but the nameplate doesn't specify the relief valve setting. I think that must be in a different part of the ASME code, and depends upon the design working pressure.

In the case of air compressors, I know that some manufacturers think that complying with the ASME code for the tank is overkill. And they charge more for an ASME stamp. When it comes to pressure vessels, I appreciate overkill. I know of a man that was killed when a compressed air tank ruptured. Of course, there is more stored energy in a compressed air tank than a hot-water boiler.
 

Last edited by Mike Speed 30; 11-13-09 at 05:25 PM.
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