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Thread: Expansion tanks

  1. #1
    DIY Member mariner's Avatar
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    Default Expansion tanks

    Hi,

    Please bear with me on this as I am not quite clear about the expansion tank issue.

    First, my water supply is from a well, it comes into the house through a check valve and then into a pressure tank at a tee in the line. The water also goes through filter and softener and then to the house via the hot and cold lines. There is no other expansion tank fitted anywhere.

    I find there is a noticeable change in pressure when in the shower, when water is turned on somewhere else in the house.

    I am thinking of putting in an expansion tank to hopefully level off the pressure changes when the shower is being used and water is used elsewhere. The extra "cushion" if you like, would hopefully reduce pressure changes.

    Would an expansion tank work ok with the connection at the bottom - with the tank verticle. Would the tank do it's intended work if above the floor boards but below sink level. I ask this as I am pushed for suitable space under the floor but could use a small closet to put the expansion tank in.

    I don't know if this makes any sense - I hope it does.

    Thanks for any and all input.

    mariner

    http://www.watts.com/pdf/1915356.pdf
    Last edited by Terry; 10-27-2008 at 11:29 AM.

  2. #2
    Master Plumber nhmaster's Avatar
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    An expansion tank will not solve your problem nor will it have any effect at all. What you have is inadequatly sized piping causing your problem.

  3. #3
    In the Trades Gary Swart's Avatar
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    As nhmaster points out, an expansion tank will not solve your problem. A thermal expansion tank is used to absorb the expansion caused by a water heater when the system is closed. It does not equalize pressure in the system. When there is a closed system without an expansion tank, when the water heats, pressure will rise in the heater resulting in the T/P valve tripping.

  4. #4
    Like an engineer alternety's Avatar
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    Do you check you filter regularly. If it is clogged it will cause what you are talking about. If the resin bed in the softener clogs, same problem.

    If either of these two devices are undersized they could cause excessive pressure drop. Was it always like this or is it something that has developed over time? If always, it is probably a design issue somewhere. If it developed, a clog or deposits inside pipes.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Assuming you have a typical well pump system (for the USA anyways), your pressure tank for the house would perform the same function as one used with a WH and a PRV.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Member mariner's Avatar
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    Default Expansion tanks

    Hi Guys,

    Thanks for the comments thus far. The inlet piping is going to be increased in size - that was already on the books. What I was interested in is using another expansion tank ($40) making two in the system, as opposed to putting a larger pressure tank ($$$'s)in the system - to achieve some cushioning or pressure damping if you like. The pressure variation/difference isn't a lot, but can be felt. The present pressure tank is 33galls (Well Rite WR120R) and I suspect a larger size would accomplish two things - reduce number of pump starts and allow better pressure delivery. The expansion tank I was looking at is around 15" dia and about 20" long (my guess) and would help to achive less starts and better fluctuations.

    If my reasoning is wrong please let me know.

    I know installing expansion tanks in rv's does reduce pump starts and evens out pressure variation better. Carrying this across to the house/home says similar improvements should be accomplished.

    Thx

    mariner

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Storing more water under pressure will slow the pressure drop, but basically, that's the way those systems work. Check on the pumps and wells forum. Cycle stop valve or (much more expensive) a variable speed pump could even the pressure out. Make sure to see if you really have the 20+ differential between the pump on/off settings. If it is misadjusted, you won't store much water or, if it is too big of a range, it stresses the bladder on the tank. Also, make sure the static pressure of the tank is proper.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default tank

    If you place a second tank at the end of the line, it will perform the work of an accumulator tank, and WILL give a bit more balanced pressure, but only because it will have the dynamics to overcome the pressure drop you are experiencing.

  9. #9
    Radon Contractor and Water Treatment 99k's Avatar
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    As suggested by alternety, is the filter clean and maintained regularly? If not, it will cause a pressure drop.
    Second. Remove the pressure switch cover and look to see the "cutin and cutout" pressure rating. You ideally should have a 40/60 switch (as long as your well can support the water useage), however, you may presently only have a 30/50 or even worse a 20/40 switch. This could be an opportunity to improve your pressure.

  10. #10
    Master Plumber nhmaster's Avatar
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    It's going to do nothing except slow down the pump cycle time, but not by much.

  11. #11
    Radon Contractor and Water Treatment 99k's Avatar
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    Quote Originally Posted by nhmaster View Post
    It's going to do nothing except slow down the pump cycle time, but not by much.
    Is this comment directed at my posting? If so, I do not agree with you and believe the pressure has an important part in this unless the piping is way undersized/clogged etc.
    Last edited by 99k; 10-13-2008 at 04:44 AM. Reason: correction

  12. #12
    Master Plumber nhmaster's Avatar
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    Adding the tank is going to do nothing for the pressure. Besides it's not pressure that is his problem, it's volume. His pipes are undersized. You could crank the pressure switch up as far as it will go and he would still have the same problem.

  13. #13
    Like an engineer alternety's Avatar
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    Pressure drop is indeed related to volume (flow) through a given resistive device (pipe, filter, etc.). But pressure is the complaint. First you should set the pressure control to 40/60 if it is not. Follow the procedure at the top of the pumps and wells forum to set tank pressure first. If the pipe to the tank from the well is too small it will make pressure fluctuation worse at higher demand rates. If your pump, under your benchmark load, runs for a real long time, and/or the pressure continues to drop while the pump is running, you are using water faster than the well can supply it. Could be the pump or the pipe; or both.

    If you could do some actual pressure measurements you can find out where the drop is occurring. The tank probably has a gauge. If you could put a pressure gauge after the filter and softener that would identify what they are contributing (while the problem water loads are running). If you are a bit handy at plumbing you could put a second gauge in there permanently. It would tell you when the filter needs to be changed.

    If it is in the house pipes, you would need a gauge at the shower to see it happen. A second tank (after the filter and softener) will provide more pressure support if the drop is in the filter and softener. The usefulness will be a function of demand flow, duration, flow rate from the source, and the size of the tank. I would not go buy a tank until I had figured this all out.

    You really ought to test pressure so you know what is reasonable. A few bucks for a gauge and a fitting is cost effective for diagnostics and has long term use.

  14. #14
    DIY Member mariner's Avatar
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    Default Expansion tanks

    Just a quick note to say thanks to all that have taken the trouble to answer my question. It is great that the forum members are so quick to help out where possible.

    Much appreciated - thank you

    mariner

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