BOOK 2, CHAPTER 8: Directional Control Valves
BOOK 2, CHAPTER 8: Directional Control Valves
Directional Control Valves
Directional control valves perform three primary functions:
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- stop fluid flow
- allow fluid flow, and
- change the direction of fluid flow.
These three functions usually operate in combination.
The simplest directional control valve is the 2-way valve, which either stops or allows fluid flow. A common example is a water faucet, manually controlled to regulate flow.
A single-acting cylinder requires both supply to and exhaust from its port for operation, which necessitates a 3-way valve. A 3-way valve allows fluid flow to an actuator in one position and exhausts it in another. Some 3-way valves have a third position that blocks flow at all ports.
A double-acting actuator requires a 4-way valve. A 4-way valve pressurizes and exhausts two ports interdependently. A 3-position, 4-way valve can stop an actuator or allow it to float. This type is common in both air and hydraulic circuits, with a 3-position, 4-way valve more common in hydraulic circuits.
The 5-way valve is most common in air circuits, and performs the same functions as a 4-way valve with the addition of an extra tank or exhaust port. This configuration is versatile for applications such as speed-control mufflers or dual-pressure inlets. Below are schematic symbols for commonly used directional control valves.
2-way Directional Control Valves
A 2-way directional valve has two ports typically called inlet and outlet. When the inlet is blocked in its at-rest condition, it is referred to as "normally closed" (NC). The boxes or enclosures represent the valve’s positions. When an operator shifts the valve, it allows flow from the inlet to the outlet. Releasing the palm button allows the valve spring to return to the normal stop-flow condition. A 2-way valve can be used for simple on/off applications but is not suitable for cycling even a single-acting cylinder.
Directional Valves: Top 5 Things You Need to Know
When selecting directional valves, there are five essential considerations:
- 2 Way, 2 Position Valves: These valves act as fluid diverters, allowing entrance and exit through two ports. "2 position" refers to "open" or "closed." They can be Normally Open (NO) or Normally Closed (NC), making them versatile for various piping systems.
- Actuation: Actuation involves an external force, like a solenoid or internal pilot, to command internal valve movements. The key aspect is the speed of fluid direction change.
- Configuration: Different 2-way, 2-position valves have varied characteristics. The configuration depends on process mediums, valve actuation, and required functions
- Size Selection: This goes beyond fitting; port size, bore, and diameter affect fluid speed and pressure, crucial for piping system integrity, especially in pneumatics and hydraulics.
- Installation and Mounting: Common 2-way, 2-position valves have threaded connections and are typically mounted in-line. Flanged valves and manifolds offer advantages for applications needing periodic maintenance.
Directional Valve Considerations
Various configurations and constructions provide different advantages, such as actuation characteristics, internal sizing, and mounting capabilities. Cost, efficiency, and location-specific considerations, like explosion-proof actuators for hazardous locations, are also essential.
Where to Buy Directional Valves
When seeking industrial-grade valves, especially complex ones, it's best to consult experts. We're the ValveMan.com store, with over 50 years in the valve business. We offer extensive knowledge and a wide range of industrial-grade directional valves, ensuring the right choice for your needs.
The company is the world’s best electro hydraulic proportional valves supplier. We are your one-stop shop for all needs. Our staff are highly specialized and will help you find the product you need.
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