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Mixing Valve Location

Johnny6Johnny6 Member Posts: 7
I am working on a project for an anodizing plant and have specific water temperatures required in five separate tanks. Each tank will recieve the temperature needs from a line drawn off of a seconadry loop. Each Supply and Return for the tanks will have a heat exchanger installed to separate the system water and the liquid in the tanks. Supply tempertures will be controlled by a three-way mixing valve on each line.

I am leaning towards installing it on the boiler side of the exchanger to protect the valve (some of the tanks will have H2SO4 in them) and have the contractor account for the temp. drop across the heat exchanger. I have never set things up this way before and am wondering if there are any potential issues by having a pump pulling through the mixing valve and then pushing into a small heat exchanger (3x8-20 plates).

I will try to add a drawing tonight to explain thing a little better. It is a bit of a backyard operation that the contractor is aware that pumps will be wrecked continuously on the tank side.


  • icesailoricesailor Member Posts: 7,265
    Mix Valve Locarion:

    Is this Potable water you are starting with? How are you protecting this? They make pumps that can take corrosive abuse but I'm not understanding how you are going to control corrosive liquids. This sounds like a very complicated job that could have code issues.

    Some here may ask for more information on how or what you want to do.
  • Johnny6Johnny6 Member Posts: 7
    More Info

    It is a unusual application for sure. We are starting with boiler water in a closed system on one side of the exchanger and a low concentration of sulfuric acid mixed with water on the other. The whole system will not have any exposure to potable water.

    I am used to putting the mixing most commonly on the transfer side of the heat exchanger not so much on the source of heat side.

    Stainless steel pumps will have some resistance to the chemicals but I have no idea what is going to happen to the impeller. We looked at using immersion heaters but to get the heat needed they took up half the space of the tank.

    This will be similar to a pool application except with low concentration sulfuric acid instead of chlorine.

    I will try to get my drawing program running tonight and add a piping schematic to the post.

    I am just curious if anyone has had issues installing mixing valves on a secondary line before the heat exchanger as opposed to installing it afterwards?
  • Mark EathertonMark Eatherton Member Posts: 5,843
    It can be done, but....

    You will experience a lag in heat transfer on initial start up. If it is a continuous run process, then it won't be a big deal. If it is a start/stop operation, due to the heat transfer characteristics of all components in the thermal stream, there will most probably be some lagging. I suspect that your 3 way valve will be wide open most of the time until the fluid temepratures start coming up, and it will then cycle in and limit source fluid temperatures.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mac_RMac_R Member Posts: 117
    Mixing Valve

    I don't know if you have started the project.  You might want to think about using a delta T control like a Tekmar that will take advantage of your secondary piping.  with that you can use a Taco or Wilo circulator on the heating side of the system and have better control over the heat you send to the exchanger.  you can then adjust your delta t to produce the proper heat on the other side of the exchanger.  A little more wiring and some programing but I think you will have better results.  I don't know what you are doing with the liquid you are heating.  But by using the Tekmar you can incorporate outdoor reset and room reset.  If it matters.
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