What is a directional control valve
The directional control valves can be used to start, stop, and to change the fluid flow in a hydraulic system. The major function of a directional control valve is to control the direction of flow in hydraulic systems. They are capable to determine the path through which the fluid should flow in a circuit. We can use the directional control valve to direct the inlet flow to a specific outlet port. Directional control valves are classified according to certain factors like inlet control element structure, number of ports or ways, number of position, method of actuation, and center position flow pattern. In a directional control valve, the internal control element would be a sliding spool, rotary spool or ball. The construction and design of the directional control valves make it suitable for different applications.
Why do we need directional control valves and for what purpose do we use a DCV
- It can be used to isolate a certain branch of the circuit
- It can vent the relief valve by either mechanical or electrical control
- It can allow free flow from the pump to the reservoir at low pressure during the time in which the delivery of the pump is not needed in the system
- It can also start, stop, accelerate, decelerate, and change the direction of motion of a hydraulic actuator.
What is the function of a directional control valve
The major function of a DCV is to control the flow or direction of the fluid in any hydraulic system. It can also choose the fluid flow path in a circuit.
What are the types of directional control valves
- Check valve
- Pilot operated check valve
- Three-way and four-way valves
- Manually actuated valve
- Pilot actuated valve
- Solenoid actuated valve
- Shuttle valve
How to actuate the directional control valves
Directional control valves can be actuated in many ways. Actuation is the process of moving the valve element from one position to another. So in a directional control valve, there are four methods of actuation they are manual, mechanical, solenoid-operated, and pilot-operated.
How does a directional control valve work
The operation of the directional control valves is determined by certain factors they are spool-type, spool positioning, method of control, and special features. If all of these are selected properly then the proper flow regulation can be achieved. The operation method of the control valve is described in the following sections.
Directional control valves are operated in two method
- Solenoid operated valve
- Pilot operated valve
How directional control valves are classified
According to the port type
Two-way valves
This type of valve can direct the flow of the pump to either of two paths of the circuit. The spool that is used in this valve would be two-way two-position valves and these valves are normally open.
Three-way valves
This type has three ports and they are mostly spool designed rather than poppet designed. These valves may block or allow the fluid flow from the inlet to the outlet. These valves have three inlets and they are pressure inlet, an outlet to the system, and return to the tank.
Four-way valves
These valves are capable to control double-acting hydraulic cylinder and it can also control bidirectional motors. Four-way DCV valves has four ports in which two of them would be outlet ports and the other two would be pressure inlet and return to the tank.
According to the method of actuation
Actuation is the process in which the element of the valve will be moved from one position to another.
Manually
In the manual actuation method, DCV valves are either actuated by push button, lever or by a pedal
Mechanically
In mechanical actuation type, spring or ball is used to actuate the DCV
DCV can also be actuated by pilot pressure or by using an electrical solenoid
According to the internal moving part construction
Poppet type – in which a piston or ball moves on and off the seats
Rotary type – in this type the spool rotates about its axis
Sliding spool – in this type the spool will slide in a bore axially, and the spool is also classified as two types as the closed center and open center spool. The closed center spool blocks all valve ports from each other in a normal position while the open center pool all valve ports are open to each other when the valve is in normal position.
According to the fluid path
Check valve
The check valve is a type of directional control valve, this valve would allow the flow of fluid in one direction but blocks in other direction. It is called a two-way valve because it has two ports.
Shuttle valve
Shuttle valves can connect two alternate flow source to one branch circuit. These valves have two inlets and one outlet. The flow reaches from the inlet to the outlet so in this valve, there are two inlets so the inlet that has high-pressure flow will reach the outlet. If the flow pressure of one of the inlet is high then the ball will move to the other side and the flow will reach the outlet.
According to the construction type
- Spool
- poppet
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