Directional control valves (DCVs) are among the most critical parts of any pneumatic or hydraulic system. This is because they allow the fluid (hydraulic oil, water, or air) to flow into different channels from one or more sources. Hydraulic DCVs are typically composed of a spool inside a cylinder that is electrically or mechanically actuated. The positioning of the spool will permit or restrict the flow of the fluid, thus, dictating the fluid flow inside the system.
How Do Hydraulic Directional Valves Work?
The spool, also known as the sliding type, has lands and grooves. The lands work to inhibit the oil flow past the valve body. On the other hand, the grooves give way for gas and oil to flow around the spool and past the valve body. The standard directional control valve in a hydraulic or pneumatic system has two primary positions: the normal and working positions. The latter position is where the valve sits after the actuating force has been removed, while the former position is where the valve sits after the actuating force has been applied. However, you should keep in mind that valve classes exist with three or more positions that the valve can sit in. Commonly, this is two or more working positions and one normal position.
How Are Directional Control Valves Classified?
Directional control valves can be classified based on;
- Number of positions
- Number of ports
- Type of spool
- Actuating methods
Operation Methods
Hydraulic directional valves are usually operated in manual, mechanical, hydraulic, or solenoid methods.
- Manual DCVs: These are common on simple paddles and levers where an operator directly inputs force to work the valve. A spring force is utilized in some instances to recover the valve position. Other manual valves use either an external hydraulic or pneumatic signal or a lever to return the spool.
- Mechanical DCVs: These are used to operate valves by leveraging forces applied through wheels, cams, and rollers; thus, the valves wear out over time.
- Hydraulic DCVs: These valves work at significantly higher pressures compared to their pneumatic equivalent. Additionally, they are precision made from higher quality materials as they are required to be outstandingly robust.
- Solenoid DCVs: These are the most advanced, and they are heavily used in industrial applications. They work by taking advantage of electromagnetic solenoids to slide the spool. The simple application of electric power provides precise control of these valves. They must supply large electrical forces to apply a matching amount of immense force. Additionally, solenoid DCVs generate heat, which can compromise the long-term reliability of the valves. As a result, most of them have a limited use cycle; thus, they are typically limited to low actuating forces.
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