Brochure

6
Number of openings in a valve
• 2-way for water/steam
• 3-way for water only
Valve Action is whether the valve is NO or NC upon power
failure. The normal position, is the flow position that the
valve will be positioned when a fail-safe actuator is
connected to the valve or the position of the valve when
zero volts is applied to a modulating actuator.
A 2-way valve body can be either stem-up-to open, which
is NO, or stem-up-to-close, which is NC. For example, for
steam, you’d always want the valve to be NC or to fail
closed, not open.
In the image above on the left, a normally open valve stem
up is open, and on the right in the stem up position is
normally closed. This also is where the valve will fail, if it’s
on power failure with a fail safe actuator.
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How valves work
NC: Normally closed
NO: Normally open
COM: Common port
For mixing the stem up position will close the bypass
port (AB-B).
For diverting the stem up position will close the
through port (A-AB).
Position of valve upon power failure when using a fail-safe actuator
There are two types of 3-way valves: Mixing and Diverting.
The internal design of the 3-way valve classifies it as a
mixing or diverting valve.
Diverting Valves – Diverting means there is one input and
two outputs, diverting the input to one or both of the
outputs. In this example on the left, the plugs are on the top
and the bottom, closing off against the direction of the flow.
Mixing Valves – Mixing means there are two inputs and one
output, mixing the two inputs into the single output. Again,
the plug closes against the flow, either against A or against B.
Although mixing and diverting valves look similar from the
outside, they have very different trim assemblies and their
applications are not interchangeable by re-piping in the field.
Normally Open (NO): Stem up to open
Normally Closed (NC): Stem up to close
A two-way valve can be either normally open, or normally closed. Three-way valves can be mixing, or diverting.
Normally Open Normally Closed Diverting Mixing