Directional Control Valve

Directional Control Valve

A directional control valve is a mechanical device you can use to control fluid flow in the hydraulic system.

These valves serve as gatekeepers in determining the allocation of pressurized fluid to designated hydraulic cylinders and controlling the direction of its flow.

Function of Direction Control Valves

Directional control valves form the backbone of the hydraulic system, they can be used to start, stop, or divert the flow of fluid within the system.

Primarily, you can use these types of valves to control flow direction in a hydraulic system by diverting the fluid flow in different directions.

Moreover, they can be employed for venting the relief valve through either electrical or mechanical control and for isolating a specific branch of the circuit.

Function of Direction Control Valves
Applications of Direction Control Valves

Applications of Direction Control Valves

Directional control valves play a pivotal role in various industries, impacting the efficiency and functionality of machinery and systems.

Some of the areas where directional control valves can be used include;

  • In a hydraulic vehicle braking system where a 3/2 valve manages the engagement and disengagement of the brakes.
  • Pneumatic systems to control fluid flow.
  • Industrial conveyor system where a 3/2 valve manages the motion of a single-acting cylinder responsible for moving a diverter arm.
  • Railway systems.
  • Mobile hydraulic machinery
  • Marine and shipment systems.
  • Manufacturing and automation i.e. a 4/2 valve controlling operations of a double-acting cylinder.
  • Aviation and aerospace systems to control landing gears.
  • Hydraulic system of equipment used in gas and oil exploration.

Directional control valves allow precise fluid flow control in hydraulic systems, offering directional regulation or blocking flow for specific maintenance or functions. Their optimal application ensures efficient operation and dependable control.

Types of Direction Control Valves

Various directional control valves have been designed to serve specific roles within the hydraulic system and they include;

Check Valves
Check Valves

· Check Valves

They are the simplest form of hydraulic devices that work by allowing fluid flow in one direction and impeding flow in the opposite direction.

Check valves distinguish themselves as entirely self-automated, they do not need manual intervention for cycling. Besides, the design of a check valve is typically straightforward, consisting of components such as a body, disc, cover, and seat.

These valves are sensitive to flow and rely on the fluid to open and close the seat. The internal disk facilitates the forward flow of fluid, leading to valve opening. When the flow is reversed, the valve closes.

However, these valves also have limitations in hydraulic systems i.e.

  • The closing element might abruptly shut, leading to potential damage and excessive wear.
  • Not suitable to be used in pulsating systems.
Pilot Operated Check Valve
Pilot Operated Check Valve

· Pilot Operated Check Valve

These valves enable unidirectional flow and only permit reverse flow when provided with a suitable pilot signal. Pilot-operated check valves work by facilitating unrestricted fluid flow from the inlet to the outlet port. Introducing pilot pressure to the designated port enables flow in the opposite direction.

Additionally, these valves provide accurate control, significant capacity, and find diverse applications making them a vital option for various industries.

However, these valves possess some limitations such as

  • The components within the pilot valve are responsive to particles, making them susceptible to contamination.
  • The soft components commonly installed in pilot valves are not resilient to fluids with raised temperatures.
  • More expensive and displays increased complexity resulting in diverse fail-open failure modes.
Three-way Valves
Three-way Valves

· Three-way Valves

A 3-way valve system contains three ports that manage and regulate fluid flow within the hydraulic system. With one inlet port connecting to two outlets in a T-shape, the valve manipulates pathways to divert fluid flow in different directions by opening or closing specific routes within its body.

These valves are frequently employed in applications requiring redirection of fluid flow between two distinct outputs or mixing of liquids. The configuration of 3-way valves renders them well-suited for low-medium-pressure tasks.

However, they are prone to wear in environments with high pressure. Moreover, their design limitations may restrict usage in applications demanding a broader range of pressure or flows.

Four-way Valves
Four-way Valves

· Four-way Valves

A 4-way valve system consists of four ports for fluid flow regulation. Unlike the 3-way valve, this system adopts an L-shaped design with two inlets and two outlets. This valve can redirect flow in two distinct directions allowing rapid changes in the fluid flow direction to reroute it to various areas.

This feature renders it a suitable system for applications requiring alternating fluid flow between outputs or diverting flow from one area to another. Additionally, these valves are also suitable for high pressure applications since they possess a more robust and durable construction.

However, they are more expensive and more complex than the 3-way valves.

Pilot Actuated Valve

· Pilot Actuated Valve

This valve comprises a body with inlet and outlet ports and also poppet biased against a spring, allowing unidirectional flow.

To enable flow in the opposite direction, pilot pressure is applied to the designated port. If the poppet’s spring force is exceeded by system pressure, it moves facilitating flow.

Some of the main advantages include:

  • Highly reliable
  • Consumes less power
  • Has high flow capability

However, the only disadvantage is that it requires a minimum pilot pressure to initiate the movement of the valve plunger.

Solenoid Actuated Valve

· Solenoid Actuated Valve

A solenoid valve is an electronically operated valve that either permits or obstructs the flow of media.

Its basic principle of operation involves a plunger moving up and down in response to the magnetic field produced by the electrical solenoid. This plunger is responsible for either opening or closing an orifice through which the media flows.

These valves can be used in various areas such as irrigation systems, air conditioning systems, dishwashers and washing machines, and medical equipment among others.

The main advantages include:

  • Has a high-cycle life
  • Capable of functioning with either DC or AC power
  • Operates with rapid response

However, these valves have some limitations such as:

  • Swift closing may result in water hammer effects.
  • Some types of media have the potential to cause clogs.
  • Flow rates may be less than those observed in certain alternative valve types.
Shuttle Valve
Shuttle Valve

· Shuttle Valve

Commonly referred to as a double-check valve, it enables pressure in a line to be sourced from alternate outlets.

During normal operations, the shuttle valve allows unrestricted hydraulic supply flow from the primary inlet port. Following this, the fluid is guided outward via the exit port towards the hydraulic cylinder.

Some of the main advantages include:

  • Allows for direct linkage to operational components
  • The shuttle valve functions to separate the compromised supply line in the event of a rupture or leakage in either of the dual supplies.

Other limitations include:

  • In the absence of an effective seal in the shuttle (to prevent blockage), leakage occurs.

However, this type can be in various applications such as hydraulic excavators or cranes, as part of braking systems, or in sub-sea applications as a hot standby.

Classification of Direction Control Valve in Hydraulic Systems

Directional control valves can be classified based on factors such as the method of actuation, the number of ports or ways,  the number of positions, the structure of the inlet control element, and the flow pattern in the center position.

Based on the Method of Actuation

Actuation is a process by which a valve’s elements transition from one point to another.

This process can be done through various methods, such as;

  • Mechanical actuation method where a ball or spring is employed to activate the directional control valve.
  • Manual actuation method which involves the use of a pedal, lever, or push button to actuate the directional control valve.
  • Actuation using an electrical solenoid method
  • Pilot pressure method.

Based on the Type of Port

There are three major types of valves under this classification technique, for example;

· Four-way Valves

A 4-way valve system consists of four ports for fluid flow regulation. This valve can redirect flow in two distinct directions allowing quick changes in the fluid flow direction to reroute it to various areas.

This feature renders it a suitable system for applications requiring alternating fluid flow between outputs or diverting flow from one area to another.

·  Three-way Valves

This particular category comprises three ports, typically featuring a spool design rather than a poppet design. These valves can either permit or block the flow of fluid from the inlet to the outlet. The three inlets include an outlet connected to the system, a return path leading to the tank and a pressure inlet.

· Two-way Valves

This valve category can channel the pump’s flow into either of the two paths within the circuit. The spool utilized in this valve configuration is typically a two-way, two-position design, and these valves are mostly in an open state.

According to the Internal Configuration of Moving Components

This mechanism comprises of three major types of directional control valves, i.e.

  • Rotary type– In this category, the spool undergoes rotational movement around its axis.
  • Sliding spool type– These are made to cater to various control systems, including those designed for optimal flow rates and pressures.

They are mainly of two types i.e. closed center and open center spools with both having their spool moving within a bore. The closed center spool blocks all valve ports from each other by default while the open center spool enables all valve ports to stay interconnected in their default position.

  • Poppet type– this is a directional control valve installed in housing bores through threaded connections. They are designed in a way that allows for enhanced sealing of the valve as operational pressure increases.

According to the Type of Construction

The basic structure of the directional control valve involves a spool positioned within a cylinder, where the movement of the spool regulates the initiation and cessation of fluid flow.

Additional designs include a spool (either rotating or sliding), poppet or ball designs.

According to the Course of the Fluid

Categorized into shuttle valves and check valves

Shuttle Valves

Also referred to as double check valves, it allows pressure in a line to be sourced from alternate outlets.

In their normal operations, the shuttle valve permits unrestricted hydraulic supply flow from the main inlet port. Following this, the fluid is directed outward via the exit port towards the hydraulic cylinder.

Check Valves

These are the simplest form of hydraulic devices that work by allowing fluid flow in one direction and impeding flow in the opposite direction.

The design of a check valve is typically straightforward, consisting of components such as a body, disc, cover, and seat. Besides, these valves are sensitive to flow and rely on the fluid to open and close the seat

How to Choose Direction Control Valves

Choosing the appropriate valve to manage system pressure, flow rate and the direction of flow is vital when designing your hydraulic system.

How to Choose Direction Control Valves

These valves are always selected based on;

Application Requirement

Different applications might require valves with distinct features, materials, or actuation methods to guarantee optimal performance and dependability.

For example, check valves only allow the unidirectional flow of fluid and block the backflow.

However, you can find other valves that allow the connection of two different flow sources to a single branch circuit. Therefore, depending on your application requirement, a suitable valve can be selected.

Operating Temperature

Fluctuations in temperature may result in the expansion and contraction of the sealing material. Consequently, the selection of valves can be influenced by both the ambient temperature of the system and the temperature of the media flowing through the valves.

Media Compatibility

When choosing directional control valves, you should ensure that the flowing fluid matches/compatible with the internal components of the system. Incompatibilities may result in leaks, corrosion, and additional problems that pose risks to the effectiveness and safety of the system.

Operating Pressure

When selecting valves, it’s important to keep in mind that the operational pressure must not exceed the design pressure, and maximum pressure capacity of the valve for the fluid component.

The chosen valve should be capable of maintaining pressure and functioning reliably across a wide range of pressures as required.

Size of the Valve

The flow capacity of the valve is determined by its size which should correspond to the required flow rate of the system. Measurement for flow rate is done in standard cubic feet per minute.

Actuator Style

There are various methods available that can be used to actuate directional control valves and the choice depends on the specific application requirement.

The methods include;

  • Mechanical actuation method where a ball or spring is employed to activate the directional control valve.
  • Manual actuation method which involves the use of a pedal, lever, or push button to actuate the directional control valve.
  • Actuation using electrical solenoid and pilot pressure method.
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