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Zone Valve Orifice

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by jimdeq, Sep 23, 2010.

  1. jimdeq

    jimdeq Member

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    I just opened my caleffi 1-1/4" sweat zone valves and the opening in the center is probably only a 1/2". Is this normal? My valves are located at the control panel, but would it make more sense to have them right before the load (exchanger) for flow reasons? Is reduced openings common in zone valves?

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  2. Chris S

    Chris S New Member

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    It is common in zone valves for the opening to be smaller than the pipe size. Even a "full port" zone valve will have a larger opening, but still smaller than the pipe size.
    A reduction in pipe size- a bottleneck if you will does not necessarily limit, or dictate the flow for your system. Basically, at this point the velocity of the fluid is increased, and pressure decreased . - Bernoulis equation-- this is also why wings create lift, and airplanes & helicopters fly. I had to get that in. :)
    I have never seen a Caleffi ZV in person, I'm sure HR will chime on on this as it is really his expertise what is really important is the CV- look at that.
    Install a length of 1'2" pipe into your system, in a run of 1 1/4" and then you'll see problems.
  3. jimdeq

    jimdeq Member

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    OK, I can accept that,but what about a mixing valve. If all the pipeing is 1-1/4" to the exchanger and to the DHW and adequete flow is what we all want ,how come most mixing valves on DHW heaters are done with 3/4"? Is it because most water heaters are piped with 3/4" anyway or should a person use a one inch mixing valve if possible?
  4. Chris S

    Chris S New Member

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    The mixing valves are also rated (cv) determine the flow you need, and then get the appropriate valve. In many cases 3/4 is adequate.
  5. jimdeq

    jimdeq Member

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    Let me restate, If I have 1-1/4" running accross my basement to a heat plate with a mixing valve on the opposite side and then off to 150' of 1-1/4" pex to a outbuilding. If the mixing valve was 3/4" is that a big no no.
  6. in hot water

    in hot water New Member

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    Cv is the number you want to look at for control valves. That valve has a Cv of 7.5. So 7.5 gpm will flow through with a 1 psi pressure drop. You can flow 10- 12 gpm through that valve, at 12 gpm you have about 2.5 psi drop.

    The issue is being able to close off the valve against the flow. At 7.5 Cv it has a 20 psi shut off. Valves with smaller ports will have a lower Cv, but higher shut off. The smaller hole is easier to shut off against, basically.

    We offer a valve with a Cv of 2.5, for example and a 50 psi shut off pressure.

    So you need to look at the flow you want to move through the valve and the pressure differential the pump will create, to select the correct valve. Smaller pipe size valves are available with a 1, 2.5, 3.5, 5 & 7 Cv.

    hr

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