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  1. #1
    Join Date
    May 2007
    Posts
    730

    Should I put a balancing valve in the bypass of this three way valve?

    I found a three way valve installed backwards on an air handling unit heating water coil; should have been installed with AB to piping Return but AB is connected to coil. I had already determined that the actuator needs to be replaced; the valve is about 15 years old (probably backwards since originally installed); and isolation valves are questionable about closing tightly. So I want to replace the valve when I do the actuator and be done with it instead of turn the valve around and test it. There are unions at the valve so it's a straightforward
    part-for-part changeout.

    But... There's no balancing valve in the bypass line, I don't think it needs one but I'm not sure. There is a balancing valve in the Return. The valve is a Honeywell V5013N1089, 1 1/2" globe, 29.3 Cv. Design flow is 45.0 GPM. At design, PSID through the valve is about 5.4 Feet and through the heating coil is 0.56 Feet. The valve will be AB-Return, A-Coil, B-Bypass; the valve is A-AB Equal Percentage, B-AB Linear.

    It seems to me that since the valve will have almost all of the pressure drop regardless of position that installing a balancing valve in the bypass might be straining at a gnat. I found out the hard way that three-way ball valves have greater B-AB resistance so I resolved to always install them with B as bypass. Is the B-AB resistance of this three-way globe valve, or globe valves in general, also greater than A-AB? If so, is there a way to calculate or find out the difference? I can't tell from the Product Data but wonder if the Equal Percentage versus Linear characteristic is a clue?

  2. #2
    Join Date
    Jul 2008
    Location
    Southern California
    Posts
    137
    The balancing valve should be installed in the return line on the system side of the by-pass line. That way the coil or its by-pass line will never use more water than its designed for.
    Effort is the 1st step towards failure.

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