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BASICS:
Back to
BASICS:
SOLENOID
VALVES
BY BILL REESON
Solenoid valves are usually consid- ered an accessory in the process
valve industry; however, while there is
some truth to this, these accessories
are crucial to the proper operation of
any system that uses them.
The solenoid valve has many fea-
tures that need to be considered when
creating a specification. Eight specifi-
cation points should be addressed to
correctly choose the right solenoid
valve for an application. These speci-
fication points are:
those that have three ports—a
pressure or inlet port (port 1),
a cylinder port (port 2) and an
exhaust port (port 3). A 3-way
valve’s most common applica-
tion is for process valve
automation. The solenoid valve
sends air to a spring return
actuator or cylinder, which cre-
ates rotational or linear move-
ment to open or close a process valve. In this case, the media is usually compressed
air or gas that is creating work, which is where the term “fluid power” is derived.
The power of a compressed gas or pressurized liquid is controlled to create mechani-
cal work. Three-way valves are usually referred to as 3/2 valves—they have three
ports and two positions.
; In cases where the valve is de-energized or off: The pressure port to cylinder
port 2 is open while cylinder port 4 to exhaust is open.
; In cases where the valve is energized or on: The pressure port to cylinder port
4 is open while cylinder port 2 to the exhaust is open.
; Type
; Operation
; Media
; Size
; Pressure
; Atmosphere
; Voltage
; Extras
Since the actuator or cylinder does not have a spring on one side, it must rely on
fluid power from a 4-way valve to open and close. Four-way valves can be referred to
as 4/2 or 5/2 valves, and they can have four or five ports and two positions.
More information on these eight
points is included in this article.
TYPE
The type of solenoid valve refers to
whether that valve is a 2-way, 3-way
or 4-way. A 2-way valve (Figure 1)
has two port connections—a pressure
or input port (port 1) and an outlet
port (port 2). These valves are used to
stop the flow of a fluid or start the
flow of a fluid in a piping configuration. Usually, a 2-way valve is referred
to as a 2/2 valve, which means the
valve has two ports and two positions.
The positions are: 1) on or energized
and 2) off or de-energized.
Three-way valves (Figure 2) are
OPERATION
Operation is a word used to describe if a valve is normally open (NO), normally
closed (NC) or universal (U). NO and NC refers to the state of a 2-way solenoid
valve when de-energized or off. NO, NC or U is used to describe the state of a 3-way
valve when it is de-energized or off. Below is a table that describes operation modes
of 2-way and 3-way valves.
These operational modes do not apply to 4-way valves since a 4-way functions the
Valve Type
2-Way Solenoid Valve
De-Energized
2-Way Solenoid Valve
Energized
3-Way Solenoid Valve
De-Energized
NC Operation
1 to 2 Closed
NO Operation
1 to 2 Open
U Operation
Not Applicable
1 to 2 Open
1 to 2 Closed
Not Applicable
1 to 2 Closed,
2 to 3 Open
1 to 2 Open,
2 to 3 Closed
3-Way Solenoid Valve
Energized
1 to 2 Open,
2 to 3 Closed
1 to 2 Closed,
2 to 3 Open
Enter pressure at any
port. Can be used as NO,
NC or diverter valve*.
Enter pressure at any
port. Can be used as NO,
NC or diverter valve*.
1 = Pressure Port, 2 = Cylinder or Outlet Port, 3 = Exhaust Port
*A diverter valve is used to divert media from 1 port and toggle the flow bet ween the 2 other ports.
