Valves have a unique ability to control fluid within a hydraulic system.
Directional Control Valves (DCVs) do so by directing the path of hydraulic fluid (flow) through a circuit. They are used to start, stop, slow, accelerate, and change the direction of motion in a cylinder.
The internal control element of a DCV (sliding spool, rotary spool, or ball) is designed for all these applications.
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One of the most common valve types are Sliding Spool Valves. They have different flow path configurations depending on the sliding spool design. All these sliding spool flow paths are found within the same body. Externally they look the same, internally they are different.
It is this construction that allows them to stop or shift flow suddenly, and are sometimes referred to as either &#;switching&#; or &#;bang-bang&#; valves for the sound they make when doing so.
DCVs are also more formally called discrete valves, referring to how the valves shift from one discrete position to another.
It is this construction that allows them to stop or shift flow suddenly, and are sometimes referred to as either &#;switching&#; or &#;bang-bang&#; valves for the sound they make when doing so.DCVs are also more formally called discrete valves, referring to how the valves shift from one discrete position to another.
When Are Directional Control Valves Used?
DCVs are essential with any hydraulic circuits to create bi-directional motion for a hydraulic actuator, or anything with a motor is going to benefit from their use, as they can be actuated into a variety of discrete positions for many functions.
Their usefulness derives from this process of actuation, or the movement of the valve from one position to another. Actuation makes DCVs vital instruments in controlling flow within complex hydraulic systems.
They work to actuate using these four methods:
DCVs are essential with any hydraulic circuits to create bi-directional motion for a hydraulic actuator, or anything with a motor is going to benefit from their use, as they can be actuated into a variety of discrete positions for many functions.Their usefulness derives from this process of actuation, or the movement of the valve from one position to another. Actuation makes DCVs vital instruments in controlling flow within complex hydraulic systems.They work to actuate using these four methods:
- Manual
- Mechanical
- Solenoid-Operated
- Pilot-Operated
The main function of a DCV is to start, stop, accelerate, decelerate, and change the direction of motion of a hydraulic actuator.
Some other examples of DCV usage include:
- To isolate a branch of the circuit
- To vent the relief valve
- To allow free flow from the pump to the reservoir
- How Does a DCV Work?
Broadly, DCVs have a general order of operations once called into action by hydraulic fluid flow.
The valve will shift to perform the operation and then shift back to the neutral position when completed. This action occurs instantaneously, causing fluid to accelerate and decelerate.
How the operation plays out specifically depends on variations in spool-type, spool positioning, and method of control.
Check valves, for example, are binary directional control valves that allow fluid to flow in one direction while preventing it to flow in the opposite direction.
Spring-loaded check valves work like this:
- The flow enters the input port and the pressure pushes the disc open (A-B)
- The spring closes the disc after enough back pressure is reached (C-D)
Source:
The main function of a DCV is to start, stop, accelerate, decelerate, and change the direction of motion of a hydraulic actuator.Some other examples of DCV usage include:Broadly, DCVs have a general order of operations once called into action by hydraulic fluid flow.The valve will shift to perform the operation and then shift back to the neutral position when completed. This action occurs instantaneously, causing fluid to accelerate and decelerate.How the operation plays out specifically depends on variations in spool-type, spool positioning, and method of control.Check valves, for example, are binary directional control valves that allow fluid to flow in one direction while preventing it to flow in the opposite direction.Spring-loaded check valves work like this:Source: tameson.com
As the name indicates, the directional control valve is used to control the direction of fluids. Fluids are liquids or gases.
Directional control valves are extensively used in industries for the passage of fluid in the system. It is difficult to adjust manually every control valve at the right time.
It controls the fluid flow in a hydraulic or pneumatic system by changing the position of its internal components. It permits or restricts fluid flow to the actuator by opening and closing its ports.
There is a difference between the directional control valve used for liquids and gases. The liquids exert high pressure, so the directional control valve is heavier and strong in construction, while DCV used for gases is generally aluminum.
Classification of Directional Control Valves
The below are the types of directional control valves as follows.
Based on the type of construction.
Based on the number of ports.
Based on the number of switching positions.
Based on actuating mechanism.
Based on the Type of Construction
The most basic configuration of the directional control valve is a spool inside a cylinder where the movement of the spool allows and stops the flow of the fluids through it.
Other types include a ball, spool (sliding spool or rotating spool), or poppet.
Based on Number of Ports
Two-way, three-way, four-way valves. Denoted in capital letters P (pump port), T (Tank port), A, B (supply ports), or numerals 1, 2, 3, 4 are shown on the boxes that indicate connections.
Based on a number of switching positions:
The square box represents position. The symbol of the directional control valve is made of a number of square boxes which are adjacent to each other depending on the number of positions. One, two, or three positions.
Based on Actuating Mechanism
The directional control valves are actuated by a variety of methods includes manual, mechanical, electrical, pneumatic, and hydraulic and as shown in the table below.
When the actuator has pressed the spool inside the directional control valve changes its position and controls the fluid flow.
Various Types of Directional Control Valves
2/2 way valves are for ON/OFF function for fluid supply. It can be normally open or closed.
3/2 way valves are generally used to control single-acting actuators. It can be normally open or closed.
4/2, 4/3, 5/2, 5/3 way valves are normally used for double-acting actuators.
Example:
Find below a hydraulic circuit that describes how a directional control valve works. In a 4/2 directional control valve, 4 ports, 2 positions.
When the lever is pressed, the directional control valve changes its position and controls the fluid flow.
DCV and Fluid Pressure Control Valves
Directional control valves provide a flow path to the cylinder actuation and also a return path to the tank.
Fluid pressure is controlled to perform different functions like pressure relief, sequence valve, and counterbalance valve as discussed below.
Pressure Relief valve
Pressure relief valve is used to limit the pressure in the whole system called pressure relief valve, also Safety valve. It prevents system pressure from building up and causing damage to equipment or serious hazards.
Pressure relief valves are two types, direct operated and pilot operated. Pressure relief valves are normally closed-type valves.
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The pressure relief valve is located between the pump and the direction control valve.
Sequence Valve
A sequence valve is used to ensure that a certain pressure level is attained in one branch line with the first consumer of the circuit.
Later supplied to the second consumer in a sequence manner.
Counterbalance valve
Counterbalance valve is used to avoid the uncontrolled speedy movement of the cylinder. It resists rapid changeover.
A counterbalance valve is used in earth-moving equipment. It holds the load for some time like lifting the trolley of the tractor or the trucks.
Directional Control Valves:
A Directional Control Valve controls the direction of a fluid in the hydraulic system pass through. The device redirects or stops the fluid flow with the help of internal mechanism in the valve. Valves contain ports that are external openings for fluid to enter and leave via connecting pipelines, The number of ports on a directional control valve (DCV ) is usually identified by the term &#; way&#;.
There are different types of DCVs that are classified based on the fluid path:
Check valves
Shuttle Valves
Two-way valves
Three-way valves
Four-way valves
Check Valves:
Type of DCV allows fluid flow only in one direction.
Fluid flows through the inlet, a small pressure is needed to open the valve seat in this direction. The valve opens when there is a flow through the inlet. Here in the figure above shown a ball type check valve.
Whenever there is a flow opposite to this direction the valve shuts. The pressure in the opposite direction press the ball against the valve seat, thus close the path.
Shuttle valve:
A shuttle valve allows the flow in two different directions.
Two positions of the shuttle valve are shown here. When the pressure of the flow on one side increases the valve closes the other path. The closing/opening condition for both paths are illustrated in the above figure.
Shuttle valves are used where there are two pumps which are used in a way if one fails to maintain the outlet pressure the other pump supply the flow as a backup.
Spool type valve:
Spool-type valves are commonly used as they can be transferred to two, three or more routing fluid locations between various inlet and outlet ports combinations. These are commonly used for steering control of actuators because a single valve can produce extension, retraction and neutrality:
There are three variants of spool type valve Two-way, three-way and Four-way valves:
Two-way Valves:
Two-way valves are also simple two positions ON/OFF valves but actuated by actuators such as solenoid actuators, hydraulic actuators etc.
There is normally closed and normally opened two-way valves, external actuation is needed to do the position change of the valve actuator.
A flow path is established or closed when the actuator is moved. These valves are also called as on-off valves
Three-way valves:
These valves have three nodes that&#;s why named three-way valve and three-way valves allows two positions of actuation in ON condition.
A three-way valve has two plug actuators each plug controls the flow in two different ways. The two plug positions are shown in the above figure. When one of the plugs closes a node other one opens the other node.
This normally closed valve neutralize the position of the actuator closing both the node to close the valve.
Three-way directional valves are available for manual, mechanical, pilot, solenoid actuation.
Four-way Valve:
Four-way valve or three position valves which got three working positions for the actuators to control the flow direction.
These valves are generally used to operate cylinders and fluid motors in both directions hydraulically.
These valves are available with a choice of actuation, manual, mechanical, solenoid, pilot & pneumatic. Four-way valve comes with two or three positions. One should note that the graphical symbol of the valve shows only one tank port even though the physical design may have two as it is only concerned with the function.
Three- position, four-way DCV have different varieties of centre configurations. The common varieties are the open centre, closed centre, tandem centre, floating centre, & regenerative centre with open, closed and tandem are the three basic types
If you have any additional questions or need help choosing hydraulic equipment for replacement, do not hesitate to contact Magister Hydraulics customer support.
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