# Expansion Tank Pressure?



## eddiecalder (Jul 15, 2008)

This is still site unseen for me so bear with me......

When charging an expansion tank (non-diaphragm) I always thought all you have to do is drain it completely and refill it so there is a cushion of air? A tech at my work ( an HVAC guy, but really smart ) says he has to pressurize it with a bike pump. I have never heard of doing this but wanted to check here before I put a stop to this. I told him that for a diaphragm tank but he said you can do it with a non-diaphragm as well??? 

Its on a closed loop water tower if that matters at all. 

The tank has no rating plat or anything on it.


----------



## Greenguy (Jan 22, 2011)

You can use a bike pump or the simple method is the hose you used to drain the tank, blow into it until you can't blow anymore close the drain and open up the lines.


----------



## eddiecalder (Jul 15, 2008)

Greenguy said:


> You can use a bike pump or the simple method is the hose you used to drain the tank, blow into it until you can't blow anymore close the drain and open up the lines.


Thanks


----------



## TX MECH PLUMBER (May 27, 2011)

I understand the idea of air in the tank to compress during expansion but isn't a tank with out a bladder just a storage tank ??? Won't it just get water logged with out having a bladder in it ??? All expansion tanks I've install always had a bladder with a valve stem on top


----------



## skitian (Apr 5, 2011)

Yes you have to charge the tank with air pressure equal to the pressure of the incoming water pressure. If you notice all, properly installed, non-diaphragm style tank have the inlet on the bottom. The air will stay in the to of the tank as the water pushes against. Also on any non-diaphragm tank, old pump tanks or old expansion tanks, the air will slowly work it's way out and become water logged. It takes much longer to do so, years longer, if they are pressurized properly. Keep in mind if you don't pressurize the tank, you're adding pressurized water to atmospheric air pressure, leaving you with a tiny air cushion that is insufficient for absorbing expansion. I hope that helps.


----------



## eddiecalder (Jul 15, 2008)

skitian said:


> Yes you have to charge the tank with air pressure equal to the pressure of the incoming water pressure. If you notice all, properly installed, non-diaphragm style tank have the inlet on the bottom. The air will stay in the to of the tank as the water pushes against. Also on any non-diaphragm tank, old pump tanks or old expansion tanks, the air will slowly work it's way out and become water logged. It takes much longer to do so, years longer, if they are pressurized properly. Keep in mind if you don't pressurize the tank, you're adding pressurized water to atmospheric air pressure, leaving you with a tiny air cushion that is insufficient for absorbing expansion. I hope that helps.


thanks


----------



## cityplumbing (Jun 12, 2010)

I know in a boiler system, I used to see older systems that had non diaphragm type expansion tanks that would have to be drained and refilled in order for you to apply that cushion of air.


----------



## BROOKLYN\PLUMB (May 21, 2010)

skitian said:


> Yes you have to charge the tank with air pressure equal to the pressure of the incoming water pressure. If you notice all, properly installed, non-diaphragm style tank have the inlet on the bottom. The air will stay in the to of the tank as the water pushes against. Also on any non-diaphragm tank, old pump tanks or old expansion tanks, the air will slowly work it's way out and become water logged. It takes much longer to do so, years longer, if they are pressurized properly. Keep in mind if you don't pressurize the tank, you're adding pressurized water to atmospheric air pressure, leaving you with a tiny air cushion that is insufficient for absorbing expansion. I hope that helps.


I disagree they do not need to be pressurized they are not designed to be pressurized they are sized for this and will work for many years


----------



## RealLivePlumber (Jun 22, 2008)

BROOKLYN\PLUMB said:


> I disagree they do not need to be pressurized they are not designed to be pressurized they are sized for this and will work for many years


:yes:


----------



## cityplumbing (Jun 12, 2010)

I'm going to assume if you pressurize a non diaphragm expansion tank you just end up pressurizing the entire system it's connected to. In a heating system you just defeated the purpose of a expansion tank, if it's a potable water system that pressure will just escape when you open up a faucet..


----------



## TX MECH PLUMBER (May 27, 2011)

cityplumbing said:


> I'm going to assume if you pressurize a non diaphragm expansion tank you just end up pressurizing the entire system it's connected to. In a heating system you just defeated the purpose of a expansion tank, if it's a potable water system that pressure will just escape when you open up a faucet..


Yes!!!!


----------



## skitian (Apr 5, 2011)

cityplumbing said:


> I'm going to assume if you pressurize a non diaphragm expansion tank you just end up pressurizing the entire system it's connected to. In a heating system you just defeated the purpose of a expansion tank, if it's a potable water system that pressure will just escape when you open up a faucet..


In a heating system, the non diaphragm tank is isolated with a valve and the drain is between the valve and tank. You close the valve, drain the tank, pressurize through the drain, if there isn't a snifter valve on the tank, then open the valve. The inlets on the tank are on the bottom of the tank. The air will stay in the top of the tank as the water pushes against it.


----------



## skitian (Apr 5, 2011)

Have any of you ever worked on non diaphragm pump tanks?


----------



## RealLivePlumber (Jun 22, 2008)

skitian said:


> Have any of you ever worked on non diaphragm pump tanks?


Non diaphram pump tank? No. 

Expansion tank. Yes. Hundreds. 

You put 15 p.s.i. of air pressure in it, you will be venting radiators all winter long, to get the air out. Or purging baseboard convectors forever and a day.


----------



## cityplumbing (Jun 12, 2010)

Expansion tanks, yes. Both diaphragm and non-diaphragm type. For hydronic boiler systems..


----------



## Plumberman (Jul 7, 2008)

I have put many into service and have never pressurized expansion tanks on heating water systems. 

WTH are we talking about??


----------



## cityplumbing (Jun 12, 2010)

skitian said:


> In a heating system, the non diaphragm tank is isolated with a valve and the drain is between the valve and tank. You close the valve, drain the tank, pressurize through the drain, if there isn't a snifter valve on the tank, then open the valve. The inlets on the tank are on the bottom of the tank. The air will stay in the top of the tank as the water pushes against it.


What happens after you just pressurized the tank with no diaphram and turn your valve back on?


----------



## cityplumbing (Jun 12, 2010)

Plumberman said:


> I have put many into service and have never pressurized expansion tanks on heating water systems.
> 
> WTH are we talking about??


Non diaphragm and diaphragm type expansion tanks and pressurizing them..


----------



## cityplumbing (Jun 12, 2010)

This is what I'm talking abut when I say non diaphragm type expansion tank..


----------



## Plumber Jim (Jun 19, 2008)

My understanding has been that you only drain the non diaphram type tanks and refill. they are sized larger so when you fill the system it will compress the air in the tank till it is equal. the larger tank will have more available volume to make up for what is lost due to the water compressing the air. the diaphram types are smaller and are compressed before you charge the system with water so you won't loose the volume of the tank from compression at filling.


----------



## cityplumbing (Jun 12, 2010)

Plumber Jim said:


> My understanding has been that you only drain the non diaphram type tanks and refill. they are sized larger so when you fill the system it will compress the air in the tank till it is equal. the larger tank will have more available volume to make up for what is lost due to the water compressing the air. the diaphram types are smaller and are compressed before you charge the system with water so you won't loose the volume of the tank from compression at filling.


 
Sounds right to me..


----------



## sigshooter71 (Dec 8, 2010)

You don't put air in non diaphragm tanks just drain them and refill that's your air cushion I deal with them all the time. Your better off replacing them with the right size diaphragm tank

Sent from my SCH-I500 using Plumbing Zone


----------



## eddiecalder (Jul 15, 2008)

sigshooter71 said:


> You don't put air in non diaphragm tanks just drain them and refill that's your air cushion I deal with them all the time. Your better off replacing them with the right size diaphragm tank
> 
> Sent from my SCH-I500 using Plumbing Zone


That is exactly what I thought and did. The other techs (hvac/r) insist on add pressure through a schrader valve. They were saying that they like the water level to only be about a 1/3 or the tank and use the nitrogen pressure to control the water level. 

I just drained it, broke the vacuum and refilled it. I did not add the nitrogen like they do. I think they do this so it wont water-log as quickly.


----------

