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Thread: expansion tank questions

  1. #1

    Default expansion tank questions

    I know this has been somewhat addressed in recent posts but I wasn't able to get everything I needed from them. I just had a new house built with a 66 gallon elec water heater. The county has a dual check valve at the meter therefore it's a closed system. Right after moving in we noticed water in the catch pan and called the plumber back out and he determined it to be a faulty water heater. After 3 months he finally came out to replace it. He hadn't been gone long when i looked in the pan and found more water. I drained off all the hot water and put a bucket under the pressure relief valve on the water heater and turned it back on. Sure enough it popped off again shortly which meant there was somewhere in the neighborhood of 150 psi in the entire system. I put a 100 psi gauge on a outside spigot and it pegged it. So I now know I need a expansion tank but not sure how big it should be or what type. Does the regular water pump tanks hold up to the pressure and hot water? Installation wise we were looking at putting it directly above the water heater so if it leaks the pan will catch it. Any advice would be great. I have pex plumbing and it's only rated to 165 so I'm cutting it real close. Help please.

    Here's info on sizing expansion tanks ...

    http://www.watts.com/pro/divisions/watersafety_flowcontrol/support/support_DETsizing.htm

    And here's info on expansion tank products from Watts ...

    http://www.wattsreg.com/scripts/pro-products.watts?_cfg=./db/pro-products.cfg&_fil=cat2%3d'Expansion_Tanks'.and.cat 1%3d'Water_Heater_Installation_Products'.and.div%3 d'_watersafety-flowcontrol'&_sn=pro-products&_tar=_view5_watersafety-flowcontrol
    Last edited by Terry; 01-12-2009 at 10:22 AM.

  2. #2
    Master Plumber master plumber mark's Avatar
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    Talking instal la prv valve first....

    does not sound like your plumber has a clue.....


    Install a prv valve for the whole house

    and kick it all down to about 60 lbs...


    or install it going into your water softener
    leaving the hard lines going to the outside hose bibs at high pressure

    -- whichever works for you


    then get the larger therm exp tank......(.or get two for extra overkill.).


    set it to about 80lbs...anything above that will go into the bladder.


    that should do the trick...
    Last edited by master plumber mark; 04-25-2006 at 05:59 PM.

  3. #3
    In the Trades Gary Swart's Avatar
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    Without an expansion tank in a closed system, the pressure rises beyond the limits of an 200 psi gauge, and it does it almost instantly when the heater kicks in. The Watts expansion tanks come in two sizes for residences, there is a guide on the box to help decide, but the larger one isn't much more money. You do need to regulate the pressure coming in, so a PRV would be in order. Installation is very straight forward, if you can sweat a joint (not smoke a joint) you can do this. While you are at it, I suggest you install a pressure gauge between the PRV and the expansion tank. The air pressure in the expansion tank has to be set the same as the PRV, and this gauge makes that super easy as well as giving you a visual check on your pressure. The expansion tank is charged with air just like a car or bike tire. Use a bicycle pump or compressor to do this. If you use a compressor be very careful not to over inflate the tank.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default tank

    Size is almost insignificant, since it only has to compensate for about a cup of water. It should be on the cold water side of the heater, and as long as the heater's supply valve is open, it can be anywhere in the house system.

  5. #5

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    What's the point of the prv on city water that's stable at 60 psi? Is a 4 gallon tank too much to be mounted right on top of the water heater? I cut the water heater off tonight and my daughter ran up a tub then I turned it back on and within 15 minutes the prv popped on the water heater and a temporary gauge I had on a outside faucet read 155 after the valve popped. None of the local plumbers have seen this before. I think it's the new check valves the water company is using so it's not allowing the water to expand back into the system. I'm tempted to take the check valve apart and jam it open with a screw or something. 155 psi is mighty close to the limits on the pex. I'm thinking the heat over the water heater may not be good for the expansion tank.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    The city will be very upset with you! The check valve is to prevent any potentially contaminated water YOU might create from getting others sick. Plumber never heard of this happening? I'd question his experience level! Some check valves are better than others...but it is doing exactly what it is designed to do...prevent any liquid from going back from where it came.

    Put in an expansion tank...it will solve the problem, that's exactly what it is designed to do. T off the cold water wherever it is convenient after the prv/check valve. If you are really worried in case the tank fails, you could put in a second tank, and or a PRV that releases at a lower pressure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades Bob NH's Avatar
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    If the city water system uses water towers, the water pressure is pretty stable and you don't need a PRV. If the pressure is only 60 psi, you will lose some pressure and get poorer service. Skip the PRV.

    Put in an expansion tank. If you operate as most people do, put in a 2 or 3 gallon tank and set the pressure at your normal water pressure. If you want to do science experiments to see how much pressure you can generate with the well known thermal expansion properties of water, then get a larger tank.

  8. #8

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    Quote Originally Posted by Bob NH
    If the city water system uses water towers, the water pressure is pretty stable and you don't need a PRV. If the pressure is only 60 psi, you will lose some pressure and get poorer service. Skip the PRV.

    Put in an expansion tank. If you operate as most people do, put in a 2 or 3 gallon tank and set the pressure at your normal water pressure. If you want to do science experiments to see how much pressure you can generate with the well known thermal expansion properties of water, then get a larger tank.
    It's not a matter of doing science experiments. We take showers and go out to eat and come back to 150 psi. With a 65 gallon water heater the earlier posts indicate at least a 4 gallon tank. Problem is where I'm going to put it. I live at the beach and the water heater is in a small closet. On top of it all we have very aggressive R/O water so the life expectancy will be short.

  9. #9
    Master Plumber Dunbar Plumbing's Avatar
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    Here is what you do, I don't understand why you are not following the logic given here.

    You need a high pressure PRV < Pressure Reducing Valve, you are dealing with pressure that might be spiking from use from other establishments in the area.

    Install the PRV after the dual check valve. Install a 4 gallon expansion tank between the shutoff on the cold water inlet and the top of the tank. Jog that tee perpendicular to the pipe entering the tank, turn up a 90 and then a 3/4 FIP to allow better support of the tank. If you have PEX running straight into the tank you will have to hard pipe at least a foot out of the tank to get stability for the tank, reconnect to PEX. They make all the connections to do this. Set your pressure of the expansion tank to the working pressure you set the PRV at, Watts dictates this procedure on their website and the paperwork that comes with the tank.

    *** Do not remove the dual check, it is required for a reason***

    You are flirting with disaster with the high pressure you are dealing with. The only reason I am mentioning the high pressure PRV is because they are only $35 more than the regular ones and your range can accept surges a great deal better. It's worth the money.

    If you have your water heater temp set up higher than 120 degrees this may definitely cause the high pressure along with the absence of an expansion tank.

    DO IT NOW, YOU ARE ENDANGERING YOUR LIFE
    Last edited by Dunbar Plumbing; 04-25-2006 at 08:48 PM.
    Read what the end of this sentence means.

  10. #10
    Engineer jk60's Avatar
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    If it helps, here is a picture of my installation of an expansion tank. It's right next to the water heater. Space constraints required that I install it horizontally so a proper support in a form of a 2x6 and a metal strap was added to this installation.
    Attached Images Attached Images  

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    Master Plumber master plumber mark's Avatar
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    Talking jk60 ---thats pretty!!

    I like the silver duct tape on the crooked chimmney....

    it gives it all a christmas kinda feeling.....


    but the expansion tank looks pretty solid....

  12. #12
    In the Trades Bob NH's Avatar
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    "You need a high pressure PRV < Pressure Reducing Valve, you are dealing with pressure that might be spiking from use from other establishments in the area. "

    I have no idea how other establishments in the area are going to cause spiking pressure. They would have to add enough water to the system to supply water to hundreds of other users on the system. Does anyone else here understand the logic of how that could happen? And presumably, those "other establishments" also have back flow preventers. And it is NOT a safety issue; that is taken care of by the pressure relief valve on your water heater.

    The bladder tank sees only the cold water coming into the house. Is the supplier supplying "agressive RO water"? If so, they are probably in violation of EPA regulations that require water that won't add copper corrosion products to your water.

    You can support the expansion tank about anywhere and run a piece of PEX to it if there is no way to hang it from a cold water pipe. It should be connected anywhere between the back flow preventer and the cold water inlet of the water heater.

  13. #13

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    Quote Originally Posted by jk60
    If it helps, here is a picture of my installation of an expansion tank. It's right next to the water heater. Space constraints required that I install it horizontally so a proper support in a form of a 2x6 and a metal strap was added to this installation.
    That answers my question about distance from water heater. What size tank is that? My suggestion to the plumber was to come up on the cold water side with hard copper then a tee. Take the horizonal line back to towards the wall where the cold water supply comes through and put the tank on top. That way if it does leak it should run into the water heater pan although it may cause problems dripping on the heater but I'd rather have that than water running on the adjacent hardwood floors. The only expansion tanks available locally are for water pumps and they are rated for 125psi and don't mention temperature. Obviously when the pressure goes up hot water travels backwards a little ways in the cold water line so the two concerns I have left is the weight of the tank and if they are a specialty tank versus the standard water pump tank. Thanks for the pic.

  14. #14

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    Quote Originally Posted by RUGGED
    Here is what you do, I don't understand why you are not following the logic given here.

    You need a high pressure PRV < Pressure Reducing Valve, you are dealing with pressure that might be spiking from use from other establishments in the area.

    Install the PRV after the dual check valve. Install a 4 gallon expansion tank between the shutoff on the cold water inlet and the top of the tank. Jog that tee perpendicular to the pipe entering the tank, turn up a 90 and then a 3/4 FIP to allow better support of the tank. If you have PEX running straight into the tank you will have to hard pipe at least a foot out of the tank to get stability for the tank, reconnect to PEX. They make all the connections to do this. Set your pressure of the expansion tank to the working pressure you set the PRV at, Watts dictates this procedure on their website and the paperwork that comes with the tank.

    *** Do not remove the dual check, it is required for a reason***

    You are flirting with disaster with the high pressure you are dealing with. The only reason I am mentioning the high pressure PRV is because they are only $35 more than the regular ones and your range can accept surges a great deal better. It's worth the money.

    If you have your water heater temp set up higher than 120 degrees this may definitely cause the high pressure along with the absence of an expansion tank.

    DO IT NOW, YOU ARE ENDANGERING YOUR LIFE
    The general principal I understand. However I've lived in this area for 30 years and never had these issues until I built my new house. It's not a incoming pressure problem therefore the prv is not required. The entire system is on elevated tanks. The high pressure is NOT coming from outside sources. It's all from my water heater. The water company has never heard of anyone else with this problem either. The temp is factory set at 120 and the plumber has plumbed probably 100 houses or more and never ran into this and some of them had heaters as big as 100 gallon in the large rental houses. TThe issue as I see it is the new check valves the water company is now putting in versus the old ones that were not as effective.

  15. #15
    Moderator & Master Plumber hj's Avatar
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    Default pressure

    if your pressure valves have a pipe to the outdoors, which is the right way to do it, then maybe the reason they have "never seen it before" is because no one looks at the pipe's discharge, or sees damp ground under it. If there is a leaky faucet or toilet in the house the pressure will not spike, but otherwise there is no way for it not to happen if you don't have an expansion tank installed. Pressure is equal everywhere in the house, so the exact location of the tank is not too important.

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