light commercial boiler expansion tank replacement


  #1  
Old 10-23-14, 05:45 PM
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light commercial boiler expansion tank replacement

So, I have a property that has 12 condos/apartments and have a gas fed boiler downstairs for the baseboard heating, the building is pretty old. So, it has an old steel expansion tank on it, that has started to leak, and instead of patch, I bought a new bladder style expansion tank. Now, Is it really as simple as removing the old piping and steel tank and capping, then just adding the newer style to the main supply line, and also adding an air valve? Just being cautious before I get into it. I've included some crappy drawings lol, but thanks very much for the help!

P.S. I have my dc 6th stationary license, and am taking my 3rd at the end of this year!

What I have now
Name:  boiler 1.bmp
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What I am thinking I'll have lol
Name:  boiler.bmp
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Old 10-23-14, 06:07 PM
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What's the make/model of the boiler?

Do you know if the boiler tapping that the old tank was connected to was acting as the 'air scoop' and passing air in the system back to the old expansion tank (where it belonged)?

One way to know this would be by the frequency that the old tank became waterlogged... do you have enough history to know this?

What I'm thinking is that it might be better to install the new tank on that same tapping along with a float type air vent at the top of the pipe.

I'm not sure that the 90 is going to be big enough, did you select that size based on calculations?
 
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Old 10-23-14, 06:13 PM
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Here's what I'm thinking:



If unauthorized ppl will have access to the boiler room it would be a good idea to remove the handle from the optional ball valve that shuts off the line to the tank.
 
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Old 10-23-14, 07:03 PM
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yes sir, I actually have the tag for the boiler


Name:  Screenshot_2014-10-23-21-41-28.jpg
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As for the calculations, the bladder tank I bought is enough to do the system, I even called a rep from Amtrol, and Ferguson, to double check that it was. As for the frequency, I have the slightest idea, I just started with the company a few months ago, they have class C and B buildings and where I used to work is all class A commercial. So it's a big step down, but the principles all remain the same. as for the 90, I only said to use that because the thread size on the new expansion tank is. I've already anticipated using all black piping, considering it's on the hottest side of the boiler, so using copper wouldn't make me happy on the internals. In reference to the drawing that you've made; that is pretty much the exact diagram of what we came up with.

The main thing that is stumping me is that the rep said that it needs to be installed on the suction side of the pump for the supply side, when there is only a booster pump for the return side. Does this matter much? I assume the piping is direct return.
 
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Old 10-23-14, 07:21 PM
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that is pretty much the exact diagram of what we came up with.
But that's not what you drew in the first post.

I'm talking about installing that setup where the old tank was connected to the boiler.


The main thing that is stumping me is that the rep said that it needs to be installed on the suction side of the pump for the supply side, when there is only a booster pump for the return side. Does this matter much? I assume the piping is direct return.
Back in the olden days most installers did not understand the concept of 'pumping away'.

What this means is 'pumping away' from the expansion tank connection.

Google the term and study up on it. There's a bunch of stuff on the forum about it too, search the forum for that term and read up.

Basically it's how any NEW system should be installed, but for the most part if an older system has been working fine as it was built, then there's no reason to re-do the whole thing just for that.

So, no, don't worry about the location of the tank relative to the pump. If you ever install a new system, then yes, re-do the piping at that time.


Having a hard time reading the model... I think it's " PEG - 8 - PI " is that correct?
 
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Old 10-23-14, 07:41 PM
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Lol I told you it was a crappy drawing, but the way we have it set-up is like your diagram lol. And thanks for the information in regards to the pump away. The model number is PFG - 8 - PI

Edit: nvm I misread your drawing. I see that you say to put it in place of the old one now, sorry. But the way your diagram shows is exactly what I would do on the supply side of boiler..I guess I am wrong?

P.s. thanks for helping me out!
 

Last edited by Vdubyuh; 10-23-14 at 08:30 PM.
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Old 10-23-14, 08:59 PM
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IF the supply tapping on that boiler is below the top of the pressure vessel then the air elimination is done in the boiler itself and no air elimination device is necessary in the supply piping. You WOULD have to add an automatic air vent on the tapping on top of the boiler where the expansion tank is currently fitted.

I would also strongly suggest that you add the new (bladder type) expansion tank to the suction side of the pump, or rather a few pipe diameters before the pump suction. It may work just fine connected to the old expansion tank fitting but it SHOULD be prior to the pump suction.

(And just for giggles I held the Seattle grade one (unlimited) license for many years prior to retirement. )
 
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Old 10-25-14, 08:53 AM
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But the way your diagram shows is exactly what I would do on the supply side of boiler.
No, not exactly.

Your plan would require that you also add an 'air scoop', or an 'air eliminator' or whatever you want to call it, from which the expansion tank hangs.

You WOULD have to add an automatic air vent on the tapping on top of the boiler where the expansion tank is currently fitted.
Yes, if you went with your first plan to cut into the supply pipes and add the air eliminator, tank, and vent at that location, you most definitely do NOT want to simply plug the tapping in the boiler that went to the old tank. You need an air vent there in ADDITION to whatever else you do.

it SHOULD be prior to the pump suction
I can't disagree that it SHOULD.

But... replacing the old tank with the bladder in the same location, piped as my diagram shows with an air vent at the top is functionally no different than it's been all these years. If there have been no problems with air in the system to this point, then there would be no problems with that in the future. Nothing is really changing functionally.

Placing the tank and air removal devices on the suction side of the pump helps the system more easily rid itself of air.
 
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Old 10-25-14, 11:05 AM
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I can't disagree that it SHOULD.

But... replacing the old tank with the bladder in the same location, piped as my diagram shows with an air vent at the top is functionally no different than it's been all these years. If there have been no problems with air in the system to this point, then there would be no problems with that in the future. Nothing is really changing functionally.
Which is why I wrote it the way I did. I will agree that most likely the system would be just fine connecting the bladder tank to the connection for the old compression tank. I was merely pointing out the proper connection point from an engineering standpoint.
 
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Old 10-25-14, 02:42 PM
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I was merely pointing out the proper connection point from an engineering standpoint.
Sure... understood.

You did 'strongly suggest' though.
 
 

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