Directional control valve plays a vital role in managing the flow direction and interruption of compressed air within piping systems. This valve type is the most prevalent across pneumatic applications. Based on the airflow direction handled, directional control valves can be categorized into two main groups: single-directional valves and reversing direction valves. The valves that permit airflow exclusively in one direction are known as single-directional valves, which include types such as one-way valves, shuttle valves, and dual-pressure valves. Conversely, reversing directional valves are capable of altering the airflow direction.

I. Reversing Directional Control Valves

1. Classification Methods

(1) Based on Control Method

The classification of valves can occur through various control methods, including air pressure control, electromagnetic control, manual control, and mechanical control.

(2) By Working Position

The work position of a valve is referred to as its "position," and valves with multiple positions are known as "position" valves. Examples include "two-position" and "three-position" valves. The state of the valve when no control signal is applied is termed the zero position.

(3) Valves by Number of Interfaces

Valves can also be categorized by the number of interfaces, which refers to the inlet, outlet, exhaust port—excluding control ports. Common variations include two-way, three-way, four-way, and five-way valves. This categorization results in names such as two-position two-way valve or three-position five-way valve.

(4) Core Structure Classification

Valves can be differentiated by core structure, with prevalent types being cutoff type and sliding column type.

(5) Control Signal Numbers

By the number of control signals, directional valves can be categorized as single or double control types. Single control means that one position of the valve is controlled by a signal, with the other being a reset mode through external forces. The spring return indicates a spring reset, air pressure return represents air pressure reset, while combined methods yield a mixed reset. Double control valves operate under two control signals for dual-position systems and can maintain the valve's position without changing when one signal disappears.

(6) Connection Methods

Furthermore, classification can be done based on installation connections, such as pipe connections, plate connections, flange connections, and integrated methods.

2. Notable Reversing Directional Valves

(1) Air Pressure Control Reversing Valves

These valves employ external air pressure to control circuit reversal or to open and close the valve. This external air pressure is referred to as control pressure and is ideal for use in potentially hazardous environments.

(2) Solenoid-Controlled Reversing Valves

Crucially important to pneumatic systems, solenoid reversing valves are categorized by their operating mechanisms, including direct-acting valves and those reliant on external air pressure.

1. Direct-Acting Solenoid Valves

A direct-acting solenoid valve changes direction through electromagnetic force, featuring either single or double coil configurations for control.

2. Pilot-Operated Solenoid Valves

These valves consist of small direct-acting solenoid valves and are paired with larger pneumatic reversing valves for efficient control.

3. Mechanically Controlled Valves

These valves operate by utilizing external mechanical forces, implementing various physical mechanisms to influence the valve core.

4. Manually Controlled Valves

Valves classified as manually controlled depend on human action to switch the flow direction, typically resulting in lower operational frequencies.

II. Single Direction Control

(1) One-Way Valve

These valves solely permit airflow in one direction, frequently combined with throttling mechanisms to manage actuator speeds effectively.

(2) Shuttle Valves

A shuttle valve functions akin to two one-way valves, effectively simulating an "OR" logic gate for fluid control.

(3) Double-Pressure Valves

This type of valve exhibits behavior comparable to an "AND" logic gate, reinforcing simultaneous flow control methods.

(4) Quick Exhaust Valves

To expedite the exhaust process of cylinders or pressure vessels, quick exhaust valves are strategically installed, bypassing standard reversing valves to enhance operational efficiency.