3/2-Way Pneumatic Valve
The 3/2-way pneumatic valve has three connection ports and two states. The three ports are:
- inlet (P, 1),
- outlet (A, 2)
- exhaust (R, 3)
The two states of the valve are open and closed. When the valve is open, air flows from the inlet (P, 1) to the outlet (A, 2). When the valve is closed, air flows from the outlet (A, 2) to the exhaust (R, 3).
A valve that is closed in
Circuit function of a Normally Closed 3/2-way valve
Most valves are mono-stable and return to their default position when not actuated, this is achieved
- 3/2-way mono-stable NC (Have a look in the
- 3/2-way mono-stable NO (Have a look in the
- 3/2-way bi-stable
The circuit functions can be shown with valve symbols. For the three
Symbols of 3/2-way pneumatic solenoid valves
3/2-way valves can be actuated by different means such as:
- electrically (solenoid valve)
Furthermore, the valves can be
3/2-way valves are available in several designs. The sealing mechanism of the valves can be a poppet or a spool. The valve’s main parts are the following: housing, seals, poppet (or spool) and an actuator
With direct operated valves, the spool or poppet is moved directly by the actuator. Several types of actuators are possible:
- Solenoid (coil)
- Push button
- Foot pedal, etc.
The valve closes or opens by moving the spool or poppet. Mono-stable valves return to their default position, which is accomplished by spring force. In case of indirect operation, the spool is not directly actuated by the solenoid.The valve uses the system pressure to move the spool. In order to do this an additional pilot valve is used. This pilot valve is a small direct operated 3/2-way valve. The pilot valve delivers compressed air to a small air cylinder inside the valve. The compressed air in this cylinder pushes against the piston and actuates the solenoid to switch the valve. This way, a relatively small solenoid can be used to switch the valve.Mono-stable valves are built with one coil, bi-stable valves with two coils. With a NAMUR housing (housing with standardized footprint), the valve can be fixed directly to an actuator which also meets the NAMUR standard. Manifolds can be used to save space and to group valves. Not only can several 3/2-way valves be built up into one manifold, there is a possibility to mix valves. For example, you can mount a 5/2-way valve next to a 3/2-way valve. The possible combinations
You always have to keep the environment of a pneumatic system in mind. When there are aggressive substances in the environment, the valve body and the seals have to be resistant
A 5/2-way valve can be used as a 3/2-way valve by only using only one inlet and the corresponding outlet port. With two 2/2-way
3/2-Way valves are suitable for several tasks: driving pneumatic actuators, blow-off, pressure release and vacuum applications.
Controlling a single acting cylinder
Operating a single acting cylinder is a typical application of 3/2-way valves. A single acting cylinder has one pneumatic port to fill and empty the air chamber. The cylinder moves in one direction by filling the air chamber, and returns by spring force. The 3/2-way valve either fills the air chamber or vents the chamber to the atmosphere. A basic pneumatic circuit for a single acting cylinder can found on the picture below.
Schematic representation of a single-acting cylinder drive with a 3/2-way valve
Controlling a double acting cylinder
A double acting cylinder has two air chambers. The cylinder is moved by filling one air chamber while venting the other. Each chamber has its own connection port, so in most
To drive the piston with two NC valves from position a0 to a1, one valve needs to be energized (switched on, 1) while the other needs to be de-energized (switched off, 0). The valve that is switched off lets compressed air exhaust at the port (R,3). Therefore, the piston moves
At least one of the two valves should be in the "exhaust" position, to not pressurize both cylinder ports at the same time. When both cylinder ports are pressurized, the piston movement depends on the previous state of the piston, the amount of pressure, the cylinder type, etc.
One NC and one NO pneumatic solenoid valve controlling a double acting cylinder
|NC Valve ’left’||NO Valve ’right’||Piston position|
|1||0||No stable state|
|0||1||Free movement between a0-a1|
Two NC pneumatic solenoid valves controlling a double acting cylinder
|NC valve ’left’||NC valve ’right’||Piston position|
|1||1||No stable state|
In the tables above the figures mean the following:
- 0 = valve not actuated
- 1 = valve actuated
Blow off, pressure release, and vacuum applications.
3/2-way valves are suitable for
Valve symbols of 3/2-way valves used for blow-off and pressure relief applications
Valve symbol of a 3/2-way valve used for a vacuum application
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