Expansion tank issues


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Old 02-03-21, 02:18 PM
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Expansion tank issues

Hi all

I just installed an expansion tank and I'm wondering if its working properly. I'm not sure I entirely trust my water pressure gauge and air gauge. I set the air to 60 psi and my water pressure is 61 PSI (according to my gauges). I turned everything on and there is no water in the expansion tank at all from what I can feel. I connected it with a flexible braided steel hose so I can pick it up. Doesn't feel cold on inlet side from water and just as light as out of the box. How much water should be in there at regular house pressure without hot water expansion happening? I guessed a third or half but I've got none.


Thanks!
 
  #2  
Old 02-06-21, 08:27 AM
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Well nobody replied so.......

Anyhow I got it figured out and thought I would share. I'm not sure if my air pressure or water pressure gauge is bad but one is for sure. I have a good quality hook scale. I put that on the expansion tank and it was right at 5lbs which is the empty weight. I kept draining a little water from the plumbing system to make sure I was at or close to the constant set pressure and let a little air out for the expansion tank a bunch of times over a couple days. With the piping system at or close to PRV set pressure I'm now weighing a constant 8 lbs on the expansion tank minus its 5 lb original weight = 3lbs of water = 1.36 liters in a 2 gallon tank. I could probably add a little air to the tank so its sit around half a liter but at least I know its got pressurized water in it and quite a bit of space to expand when required. Obviously this is not the normal way to get this sorted but since I had it attached on braided steel flex hos I was able to do this.

Cheers
 
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Old 02-06-21, 08:52 AM
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Look at this link, table in middle of page. Looks like 2 gallon may be too small for 60 psi.

https://www.waterheaterleakinginfo.com/expansion-tanks/

(forgot to say I think that would explain why you don't get much water in the tank at 60psi - but probably something you already thought of.)
 

Last edited by zoesdad; 02-06-21 at 11:32 AM. Reason: added "forgot ...
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Old 02-07-21, 06:49 AM
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It is not necessary for the expansion tank to have water in it all the time.

The expansion tank just needs to have air space that can be occupied by water when needed, without raising the pressure of the air cushion inside (and the pressure everywhere else in the plumbing system to match) too much and trip the water heater relief valve anyway.

It is a good idea for the expansion tank to be tethered or braced just in case a malfunction (such as bladder bursting) should result in a large amount of water (which is heavy) accumulating inside.
 
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Old 02-07-21, 06:57 AM
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Just to be clear though. You are not suggesting that he use that 2 gallon tank at 60 psi are you?
 
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Old 02-07-21, 11:11 AM
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The optimum preset pressure for an expansion tank is the water system pressure just after water usage has finished and all faucets turned off (and the pump for a well system has just finished its cycle). This is the static system pressure.

At that time there will be little or no water in the expansion tank.

Fine tuning the expansion tank with one or two PSI does not produce a noticeable change in performance

The size of the expansion tank should be at least four times the expected worst case of water expansion due to being heated The calculations are complex enough that all the consumer is given is the chart of water heater size versus expansion tank size.. It might be noted that if the air cushion in the expansion tank, with or without a bladder,were compressed to half it \s size its pressure will be doubled which means it won't happen until the pressure everywhere else in the system has also doubled. The pressure & temperature relief valve on the water heater may well trip before this pressure is reached.
 
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Old 02-15-21, 07:13 AM
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I know my expansion tank is on the smaller side of things. I've got a 40 gallon HW tank at maybe 60 psi (remember either my air gauge or water pressure gauge is not correct). With both matching at 60 PSI I never got any water weight in the expansion tank. I watched the system pressure rise after a big HW usage and still no water in the expansion tank. I'm going to buy a new water pressure gauge and plan on lowering the static pressure a little at a time till I get to 50 or it becomes an issue of pressure being too low.

The catalyst for this addition was I've had pipes bust/leak a couple times in the last few years. Whomever plumbed my house originally though bending hard copper was the fix when you measured wrong. 40 years later those bends are failing. I cut all the visible bends out when I finished the basement but some were hidden already. Easy to find when water is leaking from the ceiling right below though
 
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Old 02-16-21, 09:06 AM
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If you water tank is only 40 gallons, then it looks like according to some charts a 2 gallon expansion tank would be OK. (Here is one example: https://delcowater.org/thermal-expansion-tanks/

But if it were me I wouldnt play on the margin, the tanks arent that expensive. I think its the case you can never go wrong with a larger tank.

I dont have a hot water heater but I know sometimes (or maybe a lot of times) they are plumbed in with a flexible hose as you have done. But your installation sounds funny in that you are able to pick up the tank and weigh it while it is connected to the system. I thought those tanks were supposed to be fastened and supported and you shouldnt be able to move it without undoing something (well Im probably picturing things wrong and you loosened something in order to weigh the tank.) But I guess thats neither here nor there.

I think 40 gals will expand by 1/2 gal when heated to 70F. Sounds like you weighing method might have produced a reasonable result and actually there is nothing wrong with your setup.
 
 

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