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Pumps and Water Distribution 185: Three-Way Valves

The document discusses three-way valves and flow meters used in water distribution systems. It describes three-way valves as having either a single-seated mixing valve design with two inlets and one outlet, or a double-seated diverting valve design with one inlet and two outlets. The document also discusses installing flow meters, such as annular, orifice plate, and venturi meters, far enough away from disturbances with sufficient straight pipe lengths upstream and downstream to ensure accurate readings.

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Rohit Shrestha
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32 views2 pages

Pumps and Water Distribution 185: Three-Way Valves

The document discusses three-way valves and flow meters used in water distribution systems. It describes three-way valves as having either a single-seated mixing valve design with two inlets and one outlet, or a double-seated diverting valve design with one inlet and two outlets. The document also discusses installing flow meters, such as annular, orifice plate, and venturi meters, far enough away from disturbances with sufficient straight pipe lengths upstream and downstream to ensure accurate readings.

Uploaded by

Rohit Shrestha
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Pumps and Water Distribution 185

Figure 10-9. Two-way valve controlling water flow through a chilled


water coil. The coil is piped counter flow. There is a flow meter and
(manual) balancing valve in the return pipe.

Three-way Valves
Three-way control valves may be either single-seated (mix-
ing valve) or double-seated (diverting valve). The single-seated,
mixing valve is the most common. A mixing valve has two inlets
and one outlet. A double-seated, diverting valve has one inlet and
two outlets. The terms “mixing” or “diverting” do not indicate
the valve application, but refer to the internal construction of the
valve. The determination of which valve to use is based on where
the valve will be installed so that the plug will seat against flow.
Substituting one type of valve for the other in a system (or install-
ing either design incorrectly) will tend to cause chatter. Depend-
ing on its location in the system, either valve may be installed for
a temperature control action (mixing application) or flow control
action (bypassing application).
186 HVAC Fundamentals

Figure 10-10. Three-way mixing valve in a bypass application. The coil


is piped counter flow. There are flow meters and (manual) balancing
valves installed in the return pipe and the bypass pipe.

FLOW METERS

Flow meters such as annular, orifice plate, venturi, and cali-


brated balancing valve are permanently installed devices used for
flow measurements of pumps, primary heat exchange equipment,
distribution pipes and terminals. For flow meters to give accurate,
reliable readings they should be installed far enough away from
any source of flow disturbance to allow the turbulence to subside
and the water flow to regain uniformity. The manufacturers of
flow meters usually specify the lengths of straight pipe upstream
and downstream of the meter needed to get good readings.
Straight pipe lengths vary with the type and size of flow meter
but typical specifications are between 5 to 25 pipe diameters up-
stream and 2 to 5 pipe diameters downstream of the flow meter.

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