What Are the Advantages of Directional Control Valve？

A directional control valve is used in hydraulic systems to precisely control the flow of hydraulic fluid. The valves allow directional control of the fluid by diverting the flow in different directions.

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Detour from a source to an actuator or from an actuator to the return line are possible. This allows hydraulic cylinders or hydraulic motors to be controlled to perform movements in different directions.

In this article, we take a closer look at the functions, features and designs of directional control valves. Be sure to read on and learn more about ARGO-HYTOS solutions for hydraulics.

How do directional control valves actually work?

Directional control valves provide precise control of flow in hydraulic lines. They provide several functions that are critical to the efficient operation of a hydraulic system.

The first function of a directional control valve is to control the direction of flow. It can divert flow from a source to an actuator or from an actuator to the return line. This allows movement in different directions, such as forward and reverse movement of a hydraulic cylinder or rotation of a hydraulic motor.

Another important function of the directional control valve is to block the flow. In certain situations, it is necessary to stop the flow. This applies, for example, when a certain function is not needed or when maintenance work is being performed on a part of the system.

The directional control valve can block the flow and prevent the hydraulic fluid from entering a certain area. This allows maintenance work to be carried out without paralyzing the entire system.

What are the characteristics of directional control valves?

A characteristic feature of directional control valves is the number of connections and switching positions. Depending on the application and requirements, directional control valves with different connections and switching positions can be selected.

The number of connections indicates how many hydraulic lines can be connected to the valve. The number of switching positions indicates how many different positions the valve can take to control the flow accordingly.

By combining different connections and switching positions, directional control valves can be used in a variety of ways and allow for complex hydraulic control systems.

Another aspect is the different spool shapes of directional control valves and their functions. ARGO-HYTOS offers a variety of spool shapes for directional control valves, including:

• 4/3 directional control valve with Y spool for unpressurized float position
• Hydraulically releasable check valves
• Overcenter valves

Each spool shape has its specific function and is suitable for certain applications. Choosing the right spool shape enables optimal control of the hydraulic system and ensures reliable and precise operation.

Directional control valves with different characteristics from ARGO-HYTOS

Directional control valves are available from ARGO-HYTOS in a wide range of designs and variants. The range includes over 30 different spool shapes as standard, which are suitable for different applications and functions. In addition, we always offer our customers the option of having special spools developed and manufactured by our experts.

When selecting a directional control valve, various options are available to customize the function and actuation of the valve. We have developed ten different manual overrides to allow manual control of the valve in an emergency.

Furthermore, seven different nominal voltages of the solenoids at the coil connection are available for selection. They ensure optimum adaptation to electrical systems. Five different solenoid coils are also available for electromagnetic actuation.

The plug variants also play an important role in the installation and connection of the directional control valves. We offer nine different plug variants to enable easy and safe connection with other components of the hydraulic system.

We place great emphasis on the quality and durability of our products. Therefore, directional control valves from ARGO-HYTOS are subjected to a salt spray test according to DIN EN ISO . This ensures reliable surface protection for up to 1,000 hours.

Types of directional control valves

A common design of directional control valves are the screw-in cartridge valves. These valves are characterized by their simple assembly, as they can be screwed directly into the corresponding threaded connections. The screw-in cartridge valves allow a flexible design of the hydraulic system and can be easily adapted and extended.

Spool type design with housing

Another design of directional control valves is the spool design with housing, also known as a surface mounted valve with uniform hole patterns according to ISO 440. In this design, a spool made of hardened steel is used as a control element.

The spool is slid as a whole in the cast iron body. It can connect or close ports to change the function of the valve. The spool design allows precise control of flow. It is often used in applications where extremely precise control is required.

Modular design: Directional control valves RPEK

The modular design with directional control valves is also known as RPEK valve design. In this design, the spool is integrated into the module plates for horizontal interlinking. The valve consists of an inlet section with pressure relief valve and/or switchable pressureless circulation as well as one to eight flangeable directional control valves. The P (pressure) and T (tank) connections are looped through all sections.

The modular design offers the advantage of small dimensions, flexibility and compactness. It is particularly suitable for applications where limited installation space is available. By integrating several valves into one module, efficient and reliable control of the flow is made possible.

More designs

Another type of directional control valve is the screw-in cartridge valve in spool design. Here, a spool in a steel sleeve opens or closes radial bores. Also widely used are screw-in cartridge valves with a poppet seat, in which the spool is replaced by a hardened poppet. These designs each offer specific advantages such as simple assembly or technical leakage-free operation.

Significance of the operation and control of directional control valves

Depending on the requirements and application areas, various actuation and control options of directional control valves are available.

Actuation options for directional control valves

• Electromagnetic: Directional control valves can be operated electromagnetically. Here, the force is generated by an actuating element such as a pole tube, coil, armature or plunger. This method of actuation provides precise and reliable control of the valve.
• Manual: Manual actuation methods such as hand force or foot force are used in certain applications. They provide simple and direct control over the directional control valve.
• Mechanical: In mechanical actuation, the directional control valve is controlled by mechanical forces, for example, levers or push buttons.
• Pneumatic: Directional valves can be pneumatically actuated, using compressed air to control flow. This allows for quick and efficient control of the valve.
• Hydraulic: Hydraulic actuation uses hydraulic control pressure to move the spool of the directional control valve. This method provides precise and reliable control of the valve.

Meaning of spring return or pulse control with detent

Spring return or pulse control with detent is an important function in the actuation of directional control valves. It allows the valve to return to a specific position when the actuating force is removed. This ensures defined control of the flow and safe operation of the valve.

The detent ensures that the valve remains in the desired position even when no actuating force is applied. This is particularly important in applications where the position of the valve must remain stable over a long period of time to ensure reliable operation of the system.

Conclusion: The importance of directional control valves

Directional control valves enable precise control of flow in hydraulic systems. The valves provide directional control or block flow for specific functions or maintenance. They can be optimally used to ensure efficient operation and reliable control.

Would you like to learn more about our product portfolio? Or are you interested in an individual solution for your application? Then do not hesitate to contact the experts at ARGO-HYTOS. We offer comprehensive advice and support in selecting and implementing the most suitable valve technology for your needs.

Advantages and Disadvantages Directional Control Valves

Directional control valves are essential components of hydraulic systems. They are designed to control fluid flow direction in a hydraulic system. They manage the flow of hydraulic fluid, which, in turn, regulates the actuation and direction of hydraulic cylinders and motors. Directional control valves play a critical role in industrial machinery, and this blog will dive into their advantages and disadvantages.

Advantages of Directional Control Valves

One significant advantage of directional control valves is that they precisely control hydraulic systems’ flow direction, pressure, and fluid volume. This attribute is essential in applications such as aircraft landing gear, where accuracy is critical. Another pro is the ability to design customized hydraulic systems to meet specific application requirements, from flow direction to load pressure and control speed. Additionally, directional control valves are durable, have high-pressure ratings, and can maintain a steady flow even under high-pressure conditions.

A directional control valve is a type of valve used to control fluid flow’s direction.

Directional control valves are used in various applications, including hydraulic and pneumatic systems.

Directional control valves can be manually or automatically operated.

The main advantage of a directional control valve is that it allows for precise fluid flow control.

Another advantage of a directional control valve is that it can isolate a system from fluid loss.

Additionally, directional control valves can be used to regulate the speed of fluid flow.

Directional control valves are also relatively simple and inexpensive to maintain.

Finally, directional control valves are available in various sizes and configurations to meet the needs of different applications.

Disadvantages of Directional Control Valves

One major drawback of directional control valves is the high initial cost and the complexity of designing and installing the valve. For instance, some valves require complicated circuitry, leading to higher installation costs. A second disadvantage is the wear and tear of valve components over time, which reduces efficiency and could cause system downtime. Further, some directional control valves may be more prone to leaks or require frequent maintenance, which adds to operational costs.

Directional control valves are used to control the direction of fluid flow in a hydraulic system.

One of the main disadvantages of directional control valves is that they can leak. A directional control valve can develop leaks if not properly installed or maintained. These leaks can allow hydraulic fluid to escape from the system, leading to a loss of pressure and decreased performance.

Another disadvantage of directional control valves is that they can be expensive. Directional control valves are often one of the most expensive components in a hydraulic system.

Directional control valves can also be difficult to install. If a directional control valve is not installed correctly, it can cause problems with the hydraulic system.

Additionally, directional control valves can be difficult to repair if damaged. Because directional control valves are often located in hard-to-reach places, repairing them can take time and effort.

Another disadvantage of directional control valves is that they can restrict flow. If a directional control valve is not sized correctly, it can restrict fluid flow through the system, leading to decreased performance.

Additionally, directional control valves can cause noise in a hydraulic system. If a directional control valve is not installed correctly, it can create turbulence in the fluid, which can cause noise.

Types of Directional Control Valves

There are different types of directional control valves, each with its advantages and disadvantages. The most common types are the spool valve and the poppet valve. The spool valve is the most versatile, providing many flow path options, while the poppet valve is more robust and durable but is limited to fewer flow path options.

Applications of Directional Control Valves

Directional control valves are used in various industries, including agriculture, aviation, construction, and manufacturing. They are critical in controlling the flow of hydraulic fluid in equipment for farming, excavation, construction, and transportation. Hydraulic systems that require precise directional control are common in aviation applications, such as landing gear and flight control systems. Another application of directional control valves is in manufacturing industrial machinery, where the valves control precise flow direction and pressure in hydraulic cylinders.

Choosing the Right Directional Control Valves

Choosing the right directional control valve is essential for correctly functioning hydraulic systems. Factors such as flow rate, flow direction, pressure rating, temperature rating, and durability should be considered when selecting directional control valves. It is also vital to choose valves that fit the available workspace, meet the specific application requirements, and are compatible with other hydraulic system components.

Conclusion:

Directional control valves are essential components in hydraulic systems, providing precise control over fluid flow direction and rate in hydraulic cylinders and motors. While they offer several advantages, such as durability and accuracy, they also have drawbacks, such as high initial costs and the complexity of installation. Understanding the different types of directional control valves, applications, and factors to consider when selecting valves is essential to ensure the proper functioning of hydraulic systems. Operators must carefully evaluate their technical requirements and these valves’ compatibility and performance efficiency for optimum results.

Hydraulic fluid

Medium to transfer power in hydraulic machinery

Hydraulic fluid being poured into a storage container

A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water.[1] Examples of equipment that might use hydraulic fluids are excavators and backhoes, hydraulic brakes, power steering systems, automatic transmissions, garbage trucks, aircraft flight control systems, lifts, and industrial machinery.

Hydraulic systems like the ones mentioned above will work most efficiently if the hydraulic fluid used has zero compressibility.

Functions and properties

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The primary function of a hydraulic fluid is to convey power. In use, however, there are other important functions of hydraulic fluid such as protection of the hydraulic machine components. The table below lists the major functions of a hydraulic fluid and the properties of a fluid that affect its ability to perform that function:[2]

Function Property Power transmission and control medium

Non compressible (high bulk modulus)

Fast air release

Low foaming tendency

Low volatility

Medium for heat transfer

Good thermal capacity and conductivity

Sealing medium

Adequate viscosity and viscosity index

Shear stability

Lubricant

Viscosity for film maintenance

Low temperature fluidity

Thermal and oxidative stability

Hydrolytic stability / water tolerance

Cleanliness and filterability

Demulsibility

Antiwear characteristics

Corrosion control

Pump efficiency

Proper viscosity to minimize internal leakage

High viscosity index

Special function

Fire resistance

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Friction modifications

Radiation resistance

Environmental impact

Low toxicity when new or decomposed

Biodegradability

Functioning life

Material compatibility

Composition

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Base stock

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The original hydraulics fluid, dating back to the time of ancient Egypt, was water. Beginning in the s, mineral oil began to be used more than water as a base stock due to its inherent lubrication properties and ability to be used at temperatures above the boiling point of water. Today most hydraulic fluids are based on mineral oil base stocks.

Natural oils such as rapeseed are used as base stocks for fluids where biodegradability and renewable sources are considered important.

Other base stocks are used for specialty applications, such as for fire resistance and extreme temperature applications. Some examples include: glycol ethers, organophosphate ester, polyalphaolefin, propylene glycol, and silicone oils.

NaK-77, a eutectic alloy of sodium and potassium, can be used as a hydraulic fluid in high-temperature and high-radiation environments, for temperature ranges of 10 to  °F (-12 to 760 °C). Its bulk modulus at  °F (538 °C) is 310,000 psi (2.14 GPa), higher than of a hydraulic oil at room temperature. Its lubricity is poor, so positive-displacement pumps are unsuitable and centrifugal pumps have to be used. The addition of caesium shifts the useful temperature range to -95 to  °F (−70 to 704 °C). The NaK-77 alloy was tested in hydraulic and fluidic systems for the Supersonic Low Altitude Missile.[3]

Other components

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Hydraulic fluids can contain a wide range of chemical compounds, including: oils, butanol, esters (e.g. phthalates, like DEHP, and adipates, like bis(2-ethylhexyl) adipate), polyalkylene glycols (PAG), organophosphate (e.g. tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes), corrosion inhibitors (incl acid scavengers), anti-erosion additives, etc.

Biodegradable hydraulic fluids

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Environmentally sensitive applications (e.g. farm tractors and marine dredging) may benefit from using biodegradable hydraulic fluids based upon rapeseed vegetable oil when there is the risk of an oil spill from a ruptured oil line. Typically these oils are available as ISO 32, ISO 46, and ISO 68 specification oils. ASTM standards ASTM-D-, Guide for Assessing Biodegradability of Hydraulic Fluids and ASTM-D-, Standard Classification of Hydraulic Fluids for Environmental Impact are relevant.

Anti-wear hydraulic fluids

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Anti-wear (AW) hydraulic oils are made from a petroleum base fluid and commonly contain the anti-wear additive Zinc dialkyldithiophosphate (ZDDP). This additive works to protect the hydraulic pump. They come in multiple viscosity grades that have varying applications. For example, AW 46 hydraulic oils can be used to operate the hydraulic systems in off-road equipment such as dump trucks, excavators, and backhoes, while AW 32 hydraulic oils may be more suitable for colder weather applications like in a snow plow's pump.[4]

Safety

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Because industrial hydraulic systems operate at hundreds to thousands of PSI and temperatures reaching hundreds of degrees Celsius, severe injuries and death can result from component failures and care must always be taken when performing maintenance on hydraulic systems.[5]

Fire resistance is a property available with specialized fluids. Water-glycol and polyol-ester are some of these specialized fluids that contain excellent thermal and hydrolitic properties, which aid in fire resistance.[6]

Brake fluid

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Brake fluid is a subtype of hydraulic fluid with high boiling point, both when new (specified by the equilibrium boiling point) and after absorption of water vapor (specified by wet boiling point). Under the heat of braking, both free water and water vapor in a braking system can boil into a compressible vapor, resulting in brake failure.[7] Glycol-ether based fluids are hygroscopic, and absorbed moisture will greatly reduce the boiling point over time. Mineral oil and silicone based fluids are not hygroscopic.

Power steering fluid

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Power steering fluid is a sub type of hydraulic fluid. Most are mineral oil or silicone based fluids, while some use automatic transmission fluid, made from synthetic base oil.[8][9] Automatic transmissions use fluids for their lubrication, cooling and hydraulic properties for viscous couplings.

Use of the wrong type of fluid can lead to failure of the power steering pump.[8]

Aircraft hydraulic systems

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As aircraft performance increased in the mid-20th century, the amount of force required to operate mechanical flight controls became excessive, and hydraulic systems were introduced to reduce pilot effort. The hydraulic actuators are controlled by valves; these in turn are operated directly by input from the aircrew (hydro-mechanical) or by computers obeying control laws (fly by wire).

Hydraulic power is used for other purposes. It can be stored in accumulators to start an auxiliary power unit (APU) for self-starting the aircraft's main engines. Many aircraft equipped with the M61 family of cannon use hydraulic power to drive the gun system, permitting reliable high rates of fire.

The hydraulic power itself comes from pumps driven by the engines directly, or by electrically-driven pumps. In modern commercial aircraft these are electrically-driven pumps; should all the engines fail in flight the pilot will deploy a propeller-driven electric generator called a Ram-Air Turbine (RAT) which is concealed under the fuselage.[10] This provides electrical power for the hydraulic pumps and control systems as power is no longer available from the engines. In that system and others, electric pumps can provide both redundancy and the means of operating hydraulic systems without the engines operating, which can be very useful during maintenance.

Specifications

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Mineral oil base:

Mil-PRF- (originally Mil-H-): Mineral base, flammable, fairly low flashpoint, usable from −65 °F (−54 °C) to 275 °F (135 °C), red color, developed in the s[11]

MIL-PRF-: Usable from −54 °C to 135 °C "where corrosion protection is required and a determination has been made that MIL-PRF- (FRH) hydraulic fluid cannot be used. This includes use in recoil mechanisms and hydraulic systems for rotating weapons or aiming devices of tactical and support ordnance equipment, except combat armored vehicles/equipment which require FRH. The hydraulic fluid is also used as a preservative fluid for aircraft hydraulic systems and components where MIL-H- (OHA) or MIL-PRF- is used as an operational fluid."[12]

Synthetic hydrocarbon base: These synthetic fluids are compatible with mineral-base hydraulic fluids and were developed to address the low flash point draw back of mineral based hydraulic fluids.[11]

Mil-H-: Synthetic hydrocarbon base, higher flashpoint, self-extinguishing, backward compatible to -, red color, rated to −40 °F (−40 °C) degrees.

Mil-H-: A development of - fluid to improve its low temperature viscosity.

Phosphate-ester base:

US/NATO Military specification - MIL-H-

Boeing Seattle - BMS3-11

Boeing Long Beach - DMS

Boeing Long Island - CDS

Lockheed - LAC C-34-

Airbus Industrie - NSA

British Aerospace - BAC M.333.B

Bombardier - BAMS 564-003

SAE - Ac974

SAE - AS

Skydrol

Contamination

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Special, stringent care is required when handling aircraft hydraulic fluid, as it is critical to flight safety that it stay free from contamination. It is also necessary to strictly adhere to authorized references when servicing or repairing any aircraft system. Samples from aircraft hydraulic systems are taken during heavy aircraft maintenance checks (primarily C and D checks) to check contamination.[13]

Military Spec C is one fluid contamination specification.

The ISO fluid contamination scale assigns a contamination category based on particle size count and distribution.[14]

Other uses

The properties of HLP 32 hydraulic oil make it ideal for lubricating machine tools.[15][16]