Replacing old Expansion Tank

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Old 10-30-07, 11:37 AM
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Replacing old Expansion Tank

I have been reading through this website for quite some time and found it to be extremly helpful. Now I have a question that I am hoping someone will be able to answer for me as this is my first post. I have an old expansion tank that I have had to drain a few times over the last while and I have noticed it seems to be starting to rust - especially around the connections. So, I decided to replace it.

It is a fairly large one (12" in diameter by 36" tall) and it sits up between the ceiling rafters of my basement. I have done a lot of different DIY plumbing jobs before and I have even added some radiators into the loop of this system, however I now find myself at a standstill after picking up the new tank.

Here is my dilemma: the old tank has been piped from the system to a fitting on the side of the tank towards one end (the tank lying between the rafters) and on the end of the tank there is a nut that has been screwed into place that I have been loosening off and on when draining the tank - to act as a vent. That's all the connections - nothing else anywhere.

Well, I was a little confused when I picked up the new tank as there are now 2 threaded nibs on the side of the tank, and one on the end. Can someone advise me as to how this ought to be set up? I am assuming one of the side nibs is for the main line from the system; the other on the side is for a shut off valve or similar for draining; and the end one is probably just as mine is and should be capped and used as a vent? Does this make sense? I appreciate all input and thanks a bunch in advance.
 
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Old 10-30-07, 12:25 PM
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Why not replace it with a bladder tank? They don't last forever like the conventional tanks typically do, but they tend to keep the air and water doing their separate functions better.
 
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Old 10-30-07, 12:42 PM
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That is a good question and there are basically 2 reasons why not (though I am open to convincing to alter my thinking if these two don't make sense). First, I wanted to maintain the system as is - to be honest it has been working flawlessly until now and I would rather not mess around with it, plus I already bought the replacement tank. The second reason is that I was told it would require rerouting of the piping, etc. as the bladder type is not designed for between the rafters on its side and that its placement would be different from this one. I just want to replace the old tank, but this 3rd nib is throwing me for a loop!
 
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Old 10-30-07, 01:24 PM
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Best 2 changes I made on my old system were swapping out the B&G Series 100 for a Grundfos 15-58 (paid itself in reduced electric over 2 years) and getting rid of my overhead tank.

It was very easy to hang a bladder tank and add an auto air vent. I was always chasing air out of the heating branches before getting rid of it.
 
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Old 10-30-07, 03:47 PM
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The old tank didn't have a drain valve on it ? weird... exactly how were you draining it then ?

As you say, pipe from the boiler to one of the side bungs, the other side bung gets a drain valve, cap the one in the end, or if it will be accessible when installed, I guess you could add another valve there to make draining easier.

Make sure the strapping you use to secure the tank is substantial enough to support the weight of the tank when FULL of water... as you know, they do get waterlogged from time to time.
 
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Old 11-01-07, 06:20 PM
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Photo

On some expansion tanks, there are two side holes that are npt threaded to except a sight glass configuration. Is it possible for you to post a pic so that we can get an idea of what your tank looks like, then I can tell you what they are for. Still kinda odd that you dont have a main drain hole on the bottom of the tank to allow you to thread on a ball valve to drain the tank directly. Please post pic.
 
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Old 11-02-07, 05:28 AM
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my tank didn't have a drain either and I had to drain my system through the boiler drain.



Then I added a drain to my tank.



Hope that helps.
 
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Old 11-02-07, 04:00 PM
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I remember Johnny!

Hey John! I thought you drained it by removing that plug! I KNOW you remember that facefull of nasty water you got...
 
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Old 11-02-07, 05:33 PM
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Is this a pic of the new tank installed or your old setup? If you still have 2 holes on the bottom on the new tank like you have in this pic(1 for water make-up and 1 for drain) then the side holes most likely will be for a sight glass so you can see where you level is in the tank. They are VERY handy to have on the tank so you can take away the guessing game of where your water level is. Can you take some pictures of your new tank, or is that what the pic is showing, already installed?
 
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Old 11-02-07, 05:44 PM
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chitown, I belive those are pictures of John's tank, as an example for crhowell ... I guess a sight glass would be nice, but why not just drain it once a year at the start of the heating season ? I've never seen a residential tank with a glass on it.
 
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Old 11-03-07, 09:12 AM
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In my opinion a sight glass is a $40 dollar item which acts as a trouble shooting guide to tell you if your system is having problems. Of course you dont need a sight glass and continue doing maintance on the tank once a year. But, instead of just plugging the holes, why not install that $40 item, and when you go to drain the tank next time, you can fill it up to 2/3's lvl, and call it good. At that point you can always glance at the sight glass periodically and see if your system is leaking or taking on air. I work alot of commerical hvac so I always love to see a sightglass as it is a very usefull item on the tank.
 
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Old 11-03-07, 10:39 AM
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Originally Posted by chitown630 View Post
...when you go to drain the tank next time, you can fill it up to 2/3's lvl, and call it good...
chi, I'm not sure I understand you... by 'sight glass' are you talking about the vertical glass tube variety ? or just a single round eyeball ? Must be the vertical type, as seen on steam boilers...

"fill it up to 2/3 lvl" ? there is no way to do that ... the water in the expansion tank is going to find it's own level, based on the size of the tank, and the pressure in the system.

sent ya a PM ...
 
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Old 11-03-07, 11:39 AM
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I just got done working on a college campus that I was performing startups on new lochenvar boilers, 390k btu. There are expansion tanks in these systems, believe they are 40gal. I am talking about the vertical sight glass and the way these fill is with a prv valve (pressure regulating valve). These valves are set to what ever you like to set them at, so with hot water boiler systems, the best level of water in your expansion tank is 2/3's. With a sight glass you can comfirm this level in the tank instead of the guessing game of no sight glass. If I understand these pictures correctly, I see that he can manually fill the tank, which I would recommend 2/3 level. This is standard to be optimal level for a steel expansion tank, as this leaves room for expansion of water as it heats and still leaves a positive air cushion above the water in the tank to accept more water and allows the air curtain above to create pressure on existing water, therefore keeping pressure in your system.
 
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Old 11-03-07, 12:52 PM
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"...If I understand these pictures correctly, I see that he can manually fill the tank..."

Well, yeah, sorta...

That valve is there ONLY to isolate the tank from the system while draining the tank. It serves no other purpose. It's either full open, or full closed.

The water level in these conventional tanks is not 'adjustable' in that as I said in previous post, it will find it's level based on size of the tank, and pressure in the system. After you drain this type of tank, close the drain, and open the isolation valve fully, water at system pressure will enter the tank and compress the air in the tank to whatever the system pressure is set to.
 
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Old 11-03-07, 02:59 PM
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Originally Posted by NJ Trooper View Post
Hey John! I thought you drained it by removing that plug! I KNOW you remember that facefull of nasty water you got...
Hey Trooper, how could I forget that!! At times I think I can still taste that water
 
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Old 11-03-07, 04:31 PM
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Well, I must say that what ever device fills the tank (prv, gate valve, makeup water pump) your options still are the same. If you have 2 plugs on the side of the tank, and want to do more then just plug them up, then get yourself a sight glass kit(make sure you messure the height of the glass so your supply house can cut it for you). This glass will ALWAYS come in handy to let you know WHERE your water level is in the tank at ALL TIMES. For example if you tank starts to drop in water level, you form a leak of some sort in your system, this will allow you to VISUALLY see where you stand with the system, therefore eliminating guessing. If you want to help yourself you for all the heating seasons and all the servicing you do to your system, having those holes on the side of the tank allows you to install sight glass.
Dont want to keep going around, this still remains the same. Install sight glass or plug up tank. Your option.
Good Luck
 
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