Understanding 5/2 and 4/2-Way Pneumatic Valves

Figure 1: 5/2-way pneumatic solenoid valve

5/2-way and 4/2-way pneumatic solenoid valves are used for industrial automation and control systems. They are an integral component in supplying compressed air to various types of pneumatic equipment, like pneumatic cylinders. The difference in these valves is their number of ports and position states:

• A 5/2-way pneumatic solenoid valve has five ports and two position states.
• A 4/2-way pneumatic solenoid valve has four ports and two position states.

Both valve types operate similarly to control pneumatic devices, such as double-acting pneumatic cylinders. The primary difference is how the exhaust air is handled.

• A 5/2-way valve controls airflow into one port of the cylinder and controls exhaust from the other port. Due to the fifth port, this valve can precisely control exhaust coming from both cylinder ports.
• A 4/2-way valve also controls input and exhaust air to and from the cylinder. However, exhaust from either cylinder port is controlled by the same valve port, meaning exhaust rates must be identical in both directions.

Port designations

Different manufacturers use different designations for the ports. However, two primary standards are widely used throughout the industry: numbers (ISO 11727) and letters.

• 5/2-way numbers (A): Supply air port (1), outlet ports (2, 4), and exhaust ports (3, 5)
• 5/2-way letters (B): Supply air port (P), outlet ports (A, B), and exhaust ports (EA, EB).
• 4/2-way numbers (C): Supply air port (1), outlet ports (2, 4), and exhaust port (3).
• 4/2-way letters (D): Supply air port (P), outlet ports (A, B), and exhaust port (R).

Figure 2: Pneumatic solenoid valve ports are typically designated with either numbers or letters.

Circuit function

The valve's circuit function describes which ports are connected in each of the valve's states. When energized, the valve moves between one state to another, and in the case of mono-stable valves (see below), a spring returns the valve to its original position when de-energized.

• 5/2 State 1: The supply pressure port (1, P) connects to port 2 (A). Port 4 (B) exhausts through port 5 (EB).
• 5/2 State 2: The supply pressure port (1, P) connects to port 4 (B). Port 2 (A) exhausts through port 3 (EA).
• 4/2 State 1: The supply pressure port (1, P) connects to port 2 (A). Port 4 (B) exhausts through port 3 (R).
• 4/2 State 2: The supply pressure port (1, P) connects to port 4 (B). Port 2 (A) exhausts through port 3 (R).

Mono-stable vs bi-stable

Both 5 and 4 way air valves can be mono-stable or bi-stable.

• Mono-stable: A mono-stable valve's (Figure 3 labeled A & C) spool moves away from its resting position when the valve's single coil is energized. The resting position is the normal position the valve maintains when it is not energized. When de-energized, a spring moves the spool back to its resting position. Mono-stable valves require constant power to maintain the energized position.
• Bi-stable: Bi-stable valves (Figure 3 labeled B & D) have two solenoid coils. The spool moves between states depending on which coil is energized. When de-energized, the spool remains in its current state. The opposite coil must be energized to move the spool to the other position.

Figure 3: 4/2-way mono-stable (A), 4/2-way bi-stable (B), 5/2-way mono-stable (C), and 5/2-way bi-stable (D).

Design

5/2 and 4/2-way pneumatic solenoid valves are available in numerous design variations in regards to size, material, color, connection interfaces, and more. This variety is necessary to meet various requirements, such as medical use, food processing, and dusty and explosive environments.

Most of these valves have a movable spool with seals along its length, all within a central cylinder. The valve ports connect to this central cylinder. The seals block or connect to the valve ports when the spool moves through the cylinder.

Direct and pilot operated

Pneumatic solenoid valves can be direct or pilot (indirect) operated:

• Direct: The magnetic actuator directly moves the spool.
• Pilot: The valve uses inlet pressure to help move the spool. A small internal pneumatic cylinder actuates the spool. The filling and emptying of the cylinder is controlled by the valve's magnetic actuator.

Manual override

A 5/2 or 4/2 way pneumatic solenoid valve can have a manual override or lock mechanism. A lock mechanism is beneficial during maintenance; the valve does not change position until the lock is released. The actuated elements (e.g., cylinder or grippers) also retain their position. With a manual override, the system can be tested without actuating the valve. Furthermore, the valve can be manually switched by pushing the override button.

Connector types

Various connector types and designs are available that serve different purposes depending on the solenoid valve's requirements. For example, connectors can protect solenoid valves against power surges and have LED lights that indicate the valve's power status. Learn more about connectors in our DIN connector overview article.

Applications

4/2 and 5/2-way pneumatic solenoid valves can both operate double acting pneumatic cylinders and pneumatic actuators that require control in both directions. A 5 2 valve, however, with its extra exhaust port, can independently control the exhaust rate in both directions, whereas a 4/2-way valve requires both directions to share the same exhaust rate.

Controlled exhaust in both directions

• High-speed applications:In high-speed applications, such as packaging, sorting systems, or assembly lines, the speed of actuation is crucial. A 5 2 way solenoid valve with separate exhaust paths can allow for quicker exhaust of the air pressure, resulting in faster actuation times.
• Precision applications: In applications that require precise control of movement, like in robotics or precision machining, separate exhaust paths can provide better control of the speed of actuation in both directions.
• Safety-critical applications: In safety-critical applications where the failure of one part could have serious consequences, separate exhaust paths can provide redundancy. If one exhaust path fails, the other can still function.

Same exhaust in both directions

• Single-acting cylinder applications: In applications using single-acting cylinders where spring return is used, a common exhaust path (4 way valve) is sufficient since the return action is not dependent on the exhaust air.
• Less critical speed applications: In applications where speed of actuation is not critical, a common exhaust path can be used. This might include general purpose pneumatic systems, door openers, or simple mechanical movements.
• Cost-sensitive applications: 4/2-way valves can be less expensive than 5/2-way valves. If the application doesn't require high speed or precision, a 4/2-way valve might be more cost-effective.

FAQs

What is a 5/2 way solenoid valve?

A 5 2 solenoid valve has five ports and two states. It can switch between two different states to control airflow to and exhaust from both air ports of a pneumatic cylinder or actuator.

What is a 4 way solenoid valve?

A 4/2-way solenoid valve has four ports and two positions. Two ports supply air to either side of a double acting solenoid valve and the remaining port handles exhaust from the cylinder.