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Thread: Check Valves in Recirc System and Mixing Valve Cause Hammer

  1. #1
    DIY Junior Member dwheels's Avatar
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    Default Check Valves in Recirc System and Mixing Valve Cause Hammer

    I've read through the thread on Submersible Pumpbs and Multiple Check Valves. Let me describe my system before I ask my question.

    My home’s hot water system consists of:
    -2hp submersible pump at 65 ft. with a check valve near the surface. Well is 125’ from the house.
    -A 32 gal. Polaris WH that feeds both domestic HW and the home’s hot water forced air heating system.
    -A Proportional thermostatic mixing (flow control) valve to reduce water temp for the domestic side.
    -A HW recirculation system to supply the master bath 50 ft. away.

    The cold supply splits and feeds the mixing valve and the cold-in side of the WH. The original installation had two check valves. One between the cold supply and the water heater and one between the cold supply and the mixing valve. The recirc system draws hot water through the house and returns re-circulated water to the cold water supply side of the WH at a tee between the check valve and the WH cold-in.

    Problem: When the well pump cycles, the check valves slam (hammer). So, soon after installation I removed the check valves to prevent hammer and subsequent damage. No surprise--now I get backflow and uneven temperatures on the domestic supply, especially when the recirc pump is on.

    Will a cycle stop valve solve my problem and allow me to reinstall the check valves? Or, is there a better way to do this altogether? The installer removed the plastic check valves from both sides of the mixing valve. Should they be replaced?

    Also, there’s no expansion tank on the WH. Should there be?

    (Diagram Attached)

  2. #2
    Moderator valveman's Avatar
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    If the water hammer is happening on pump start up, I think the check valve being near the surface is the problem. That check should be right on the pump. Anytime there is a check valve in the line, you need an expansion tank on the WH.

  3. #3
    DIY Junior Member dwheels's Avatar
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    Valveman.
    The check valve at the well head seems to be standard around here. The driller is the biggest company in the area and it's the way they do it. The hammering stopped when I removed the two check valves at the WH mentioned without doing anything about the one at the well. (My diagram should be attached this time)
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    General Engineering Contractor ballvalve's Avatar
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    You need a check valve before the recirc pump, thats for sure. Dont think any before the mixing valve is important. But neither one is going to have anything to do with water hammer from the well. Your Installer shows some lack of experience by removing the check at the recir pump, and especially if he used PLASTIC check valves, notoriously trash [and near a water heater!] unless schedule 80, rated for temperature, and costing over 50$.

    I would put in a good spring ball check valve, SS or brass by the recirc pump. A 2 HP pump at 65 feet is massive overkill unless this is a hotel. You might have a problem with your well pump area checks [plastic again?] and a reduction in flow from the pump at shut off would likely rid you of hammer.

    I have almost the same system without the mix valve, but the well is far away. I have a pressure reducing valve on the house inlet, and do not have an expansion tank, and do not have any problems.

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    Moderator valveman's Avatar
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    I agree! Don't use the plastic checks on hot water. A pressure reducing valve probably has a thermal by-pass and doesn't need an expansion tank. Still need an expansion tank after a check valve.

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    DIY Junior Member dwheels's Avatar
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    Thanks for the info from both of you. I need to spend some time reviewing it. But, here's one more question: I've already purchased a replacement mix valve because the previous one is shot: Honeywell AM101, which has the plastic check valves installed. I would think that if it is certified for up to 212 degrees F., they would be okay(?). My system runs at about 160 degrees.

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    DIY Junior Member dwheels's Avatar
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    One more note of clarification. The two check valves in the drawing are brass. It's the check valves installed in the new mix valve and at the well that are plastic.

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    Moderator & Master Plumber hj's Avatar
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    Your mixing valve is shot because of your system, and the next one will also fail. A mixing valve can ONLY reduce temperature if a faucet is open and cold water can flow through the mixing valve. Your circulating pump is moving HOT water through it so it closes the hot side and opens the cold to lower the temperature, but there is no "flow" so the cold water is blocked. The mixing valve will then close the hot side as far as possible in a hopeless attempt to lower the temperature. At that point the pump is forcing the water through the valve damaging the seating surfaces which will then prevent it from operating properly WHEN THERE IS cold water flow available. DO NOT put any valve ahead of the pump, except one for servicing the pump. ALL operating valves, i.e., check valves, or flow modualting ones, MUST go between the pump and the water heater or you will also damage the pump. The mixing valve was designed for use with both HOT and COLD water and the integral check valves were also designed for hot water. Put the back into the valve. The check valves on the cold water lines to the heater and mixing valves are mostly cosmetic and do nothing to a properly operating system.

  9. #9
    General Engineering Contractor ballvalve's Avatar
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    Yes, with a better look at the schematic, it is plumbed incorrectly. The honeywell valve can be used but the "cold" flow must come from the recirc pump.

    http://www.forwardthinking.honeywell...62_3075efs.pdf

    There is the schematic that will show your "installer" - hopefully- to gt it right. The cold outlet from the recirc pump tee's into the cold of the mixer valve and then to the cold return from the Polaris. You have not been doing much mixing at all.

    Honeywells valve is fine with plastic integral checks, but you MUST use the schematic shown on the link.

    So hold onto your valve and buy a hacksaw and some tee's and pipe.

    OKAY; another look at your schematic- I see that mix system is for the fixtures, not radiant. {I believe} but my point still stands, and HJ can review it, that you need to get flow to the cold inlet from the recirc pumps outlet for those times when a faucet is NOT open AND the recirc is running.

    Notice where Honeywell places the incoming check valve on the cold line.
    Last edited by ballvalve; 05-12-2010 at 10:52 AM.

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    DIY Junior Member dwheels's Avatar
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    Ballvalve.
    I can see that according to the Honeywell schematic I need to move the check valve to the high pressure side of the recirc pump. However, I'm still confused about whether or not the plastic valves at the output sides of the mix valve should be kept. Especially when the two check valves in line to the cold side of the mixer accomplish the same thing. Also, I'm concerned about the slamming (hammer) I get when the well cycles with the brass valves installed. (Remember, removing the valves stopped the hammer but messed up the mixing operation.)

    Sorry, I'm probably making this more difficult than it needs to be.

  11. #11
    General Engineering Contractor ballvalve's Avatar
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    You need to repipe the outlet flow from the recirc pump. with a tee that goes to the inlet [cold side][ of the mixer and the the other leg to the cold return on the Polaris. Honeywell designed the valves for high temps.

    They show a check valve on the inlet cold from the pump only.

    Water hammer at the well is not a product of check valves at a water heater. You need to state if you have hammer on pump start or pump stop. You probably need to restrict the output from your oversized pump. Hammer is caused by a fast flow of water shut off quickly. Look into dole valves and the CSV.

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    DIY Junior Member dwheels's Avatar
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    Many thanks to all for you input.

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