Do you know the principle of directional control valve?

Directional control valve serves as a vital component for controlling the flow direction and air flow interruption in compressed air pipelines. This type of valve is predominant in pneumatic systems due to its functionality. Depending on airflow direction, directional control valves fall into two major categories: one-way directional control valves and reversing directional control valves. One-way directional control valves permit airflow in a singular direction and include one-way valves, shuttle valves, and dual-pressure valves. Conversely, reversing directional control valves are capable of changing airflow directions, often referred to as reversing valves.

I. Reversing Directional Control Valves

1. Classification

(1) Classifying by valve control methods allows for categories such as air pressure control, electromagnetic control, manual control, and mechanical control.

(2) The working position of a valve, referred to as a “position”, allows for further classification into “position” valves with multiple switching working positions. Examples include “two-position” valves and “three-position” valves. The state of the valve without a control signal is termed the zero position.

(3) Valves can also be categorized based on the number of valve interfaces, termed “through” interfaces. Existing valves may include two-way, three-way, four-way, and five-way varieties. The valve name typically reflects its switching position and the number of interfaces, such as two-position two-way valves or three-position five-way valves.

(4) Valves can be classified by their core structure into cut-off type and sliding column type.

(5) The control number classification divides valves into single control types and double control types. A single control type allows one valve position through a control signal while a different force determines another position. For example, a spring reset denotes that control comes from spring force, whereas air pressure reset indicates the use of air pressure for reset. Mixed reset optimizes the valve core reset piston diameter, leading to enhanced switching reliability and operation stability. A double control type indicates that two control signals are employed. For two-position valves, this allows the maintenance of the original position despite the disappearance of one control signal, offering a memory function.

(6) Finally, valves can be classified based on their connection installation methods, which may involve pipe connections, plate connections, flange connections, or integrated connections.

2. Notable Reversing Directional Valves

(1) Air pressure control reversing valves rely on external air pressure signals to switch the main valve and control circuit operations. Safety makes air pressure control suitable for flammable, explosive, humid, and dusty environments. These valves can be categorized into three types based on their functioning: pressure control, pressure relief control, and differential pressure control.

(2) Solenoid-controlled reversing valves rank among the key components in pneumatic systems. There are direct-acting solenoid valves and those defined by their power supply, whether DC or AC.

1. Direct-acting solenoid reversing valves utilize electromagnetic force for direct core movement. They can have single or double coils, classifying them into single solenoid control or double solenoid control, respectively. While their structure is compact and offers high reversing frequency, an AC electromagnet can burn coils if the valve stem becomes stuck. Thus, these valves are suitable for smaller applications.

2. Pilot-operated solenoid reversing valves integrate smaller direct-acting solenoid valves with larger pneumatic reversing valves.

3. Mechanically controlled reversing valves activate through the mechanical force of an actuator or similar mechanism, using means such as cams or levers for directional changes.

4. Finally, human-controlled reversing valves rely on manual operation via hand or foot, but they exhibit limited operating frequency.

II. One-Way Direction Control

(1) One-way valves permit airflow exclusively in one direction and are commonly used in tandem with throttle valves to regulate actuator speed.

(2) Shuttle valves function as a composite of two one-way valves, demonstrating the logical capabilities of an "OR" gate.

(3) The double-pressure valve mimics the function of an "AND" gate logical operation.

(4) Quick exhaust valves are crucial for discharging air rapidly from cylinders or pressure containers. When positioned between the reversing valve and the cylinder, these valves expedite cylinder movement by facilitating direct gas evacuation, especially advantageous for distant setups.