expansion tank keeps getting water logged

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Old 03-28-11, 02:49 PM
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expansion tank keeps getting water logged

i need to drain my tank down after the furnace is allowed to cool down completly. i may not have noticed this in the past, because i used to run the furnace all year for hot water. about 2 years ago i switched to an instant hot water heater. the first season i used the furnace after being off all summer, i had a problem because the expansion tank was water logged. ( i posted here and got some good advice on how to fix it). this year i had shut the furnace down 2 times and after starting from cold i noticed i have to bleed out a lot of air from one of the radiators, after that the pressure goes up and i need to drain the tank. all is good until the cool down occurs again. when i posted some pictures fo my system last time, there was a few comments about the way the pipe is run to the tank. could this cause my problem??
here is the link to the pictures.
100_2867 | Flickr - Photo Sharing!

100_2866 | Flickr - Photo Sharing!
 
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Old 03-28-11, 03:33 PM
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All that tank will ever get is water in it the way it is piped.
The way the system is supposed to work is,
return water comes back to boiler, and gets heated. Any air that is in solution should now be out due to heating.
If the air cushion tank is piped either off the top of the boiler as certain manufacturers suggest, or off a tee leading out to the supply system. But air raises, and if there is an air trap as you have leading to the tank then the air will get to the tank, it will bypass and go into the system. You then bleed it out, it collects again. etc etc...
If you pipe that air cushion tank into the system where the air will come off the top of a tee, or even better an air scope then you stand a decent change.
Depending on where the system circ is, you may be able to hang a diaphragm expansion tank off of that drop.
 
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Old 03-28-11, 03:36 PM
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Yes, there is a problem in how your piping runs to the expansion tank. It needs to run continuously uphill, not go up and then take a dip downward into the tank.

I would advise you to abandon that tank and install a properly sized diaphragm tank. The diaphragm tank best belongs before the circulation pump suction but can often be placed anywhere in the system.
 
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Old 03-28-11, 06:02 PM
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Dont forget to add air vents if you go to a bladder tank.

Mike NJ
 
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Old 03-31-11, 06:16 AM
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switching to a diaphragm tank

if i have to switch to a diaphragm tank what size should i get? the steel tank is 36" long and 12" round. the circulation pump is located right off the back of the furance ( about a foot or two off the floor). does the pump pull on the system or out of the furnace.
you can see in this picture:
100_2846 | Flickr - Photo Sharing!
can i just intsall the new tank in the same location?
if i do switch to a diaphragm tank , what is the procedure for filling the system and bleeding the radiators?
please let me know if i need to provide any more info and thanks for the help.
 
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Old 03-31-11, 04:00 PM
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You could mount it in the same location. It's not ideal but it will work pretty much the same as the old one did.

BUT

You will also need to install an air removal device such as an 'air scoop', or a 'SpiroVent'. You can't leave the air in the system (even though it apparently has been working that way for a LONG time!)

In order to properly size the expansion tank, you would need a fairly close estimate of the volume of water in the system.
 
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Old 03-31-11, 04:12 PM
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Missed the question about the pump...

Your pump is on the RETURN from the system to the boiler. The pipe on top of a boiler is always the HOT supply out of the boiler to the system. That's the one that goes up to the red flow check valve that the tank is piped to.
 
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Old 03-31-11, 07:21 PM
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what about changing the pipe not the tank?

i was thinking that my problem seems to be caused by the pipe going into the expansion tank drops down then back up.
would i be able to shorten the straight pipe going up to the red flow check valve to run a pipe up to the expansion tank?? i think i could do this by using a shorter straight pipe (the pipe is 22" long now) going into the flow check valve and some elbows to get it back to the system pipe. for the tank maybe one elbow then straight up to the tank.
any thoughts or cautions??
 
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Old 03-31-11, 08:21 PM
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The pipe from the exp tank to the flow check needs to have pitch. Higher at the exp tank and lower at the flow check. It dont look like you can do it.


Possibly you can tie in elsewhere. Take so pics of your boiler as a whole at different angles so we can see what you got.

Have you thought about replacing that dinosaur?

Mike NJ
 
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Old 04-02-11, 08:59 AM
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Have you thought about replacing that dinosaur?
I've said this before... I think that whole system should be a museum piece! For all original stuff it's in remarkable condition! I love that Everhot water heater!

From what I can see in the pics, there is a union connection where the horizontal pipe meets the SA flow check valve. If you were thinking about changing to a bladder tank, I would think that horizontal section would be the easiest solution. You could remove that piece of pipe rather easily (because of the union there), and place a Spirovent along that run and hang the bladder tank from it.

While this solution is not ideal in terms of the 'pumping away' strategy that we've come to consider 'best', you would be no worse off than you are now...

Let's see those wider angle shots of the system so we can get some perspective.
 
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Old 04-02-11, 09:04 AM
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While shortening that vertical pipe off the boiler seems like a good solution, what you should consider is the fact that there is no place to collect the air in the system and route it back to the expansion tank. That is what is supposed to happen...

With the existing setup, not only can the air NOT get back into the tank, there is no means for air to even be collected at that point anyway.

Going to all the trouble of shortening that pipe and re-doing the pipe to the tank isn't going to gain much (if any) benefit.
 
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Old 04-10-11, 11:31 AM
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more furnace pictures

sorry this took awhile. i added 3 more pictures of the furnace.
furnace pics - a set on Flickr
hope these help.
after reading what NJ Trooper had to say
While shortening that vertical pipe off the boiler seems like a good solution, what you should consider is the fact that there is no place to collect the air in the system and route it back to the expansion tank. That is what is supposed to happen...
i don't think i fully understand what is supposed to be happening. i was thinking that the problem is caused by the "j" in the pipe going down then up to the tank and if i lower the flow check valve so the pipe could go straight up to the tank it would work properly.
it seems that this problem has always been there, but if i started with draining the expansion tank, filling it and bleeding the radiators the pressure would be fine until the furnace was allowed to cool down completly. then i would have to do this all again. the first 13 years i have owned this house we used the furnace for heat and hot water so it never completly cooled down unless i shut it down (most likely only for service). now i only use it for heat it gets shut down more often. so i would like to try and find a solution that is cost effective and doesn't result in replacing the furnace.
thanks again for all of your help.
 
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Old 04-10-11, 06:23 PM
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thinking that the problem is caused by the "j" in the pipe going down then up to the tank
That's really only part of the problem... so it does need to be addressed, but:

What is supposed to happen ideally is that any air that is flowing through the system at any time needs to be 'collected' and routed back to the tank. The only way to do that is to have an 'air scoop' in the main line and pipe the tank off the top of that.

The way the system is currently piped up any air that is in the water is going to go rushing right past that tank connection and back out into the system.

In order for air to be collected, it has to enter a place where the water slows, and the pressure drops. Air scoops provide that place by increasing the size of the pipe at that point. Along with that there are 'baffles' in the scoop that directs the air upward.

So, even if you did remove the 'trap' going to the tank, there is nothing under it to collect the air and you would not gain much of anything, IF anything...
 
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Old 04-20-11, 07:55 PM
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would it be possible to install a b/g inline air separator below the flow check valve? on the b/g web site it says you can use it with both types of expansion tanks.
 
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Old 04-20-11, 08:10 PM
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It needs to be installed horizontally...
 
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Old 04-24-11, 03:41 PM
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i have posted a diagram of what i think i need to do to install a b/g air separator.
furnace diagram2 | Flickr - Photo Sharing!
please let me know if anyone can see a problem with this set up.
thanks again
 
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Old 04-24-11, 04:41 PM
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The air problem

The air cushion and the air seperator are usually two seperate functions. Example; if you change that tank on the ceiling to a blader tank, as in your photo sample, you will be collecting air in the water side of the blader. You need to put an air valve on top of the air seperator, and just pipe directly from your circulation to ethier of your chosen air cushion tanks. I hope that makes sense.
Sid
 
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Old 04-24-11, 05:56 PM
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Sid, I think he's trying to keep the old tank... but,

You don't install the IAS in that fasion. The port on the bottom is only 1/2", and isn't intended as an inlet. You need IN on one end, and OUT on the other, IN-LINE... there may be recommendations from B&G that a certain length of straight pipe exist ahead of the IAS. You don't want a turbulent flow coming straight out of an elbow.

And when/if you do repipe, unless you have a strong sentimental attachment to that gate valve, replace it with a full port ball valve.
 
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Old 04-26-11, 06:45 PM
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thanks, i don't know why i didn't see that. i uploaded a new diagram
furnace diagram3 | Flickr - Photo Sharing!
i found on pex supply web site they said the minimum straight length of pipe before the air separator is 18"( it did not say anything about the outlet side)
i did some measurements and i think i have enough room to do it this way. also just a typo, i would only use full port ball valve in place of the gate valve.
let me know if anyone can see a problem with this setup.
 

Last edited by mech1; 04-26-11 at 06:47 PM. Reason: missed a word
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