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MDP Hydraulics
The threaded cartridge-type directional control valve is a modular hydraulic control component that is directly installed in the hydraulic integrated valve block through standard threaded insertion. It is specifically designed to control the flow direction, on-off, and direction change of the oil in the hydraulic system. It is the core component for constructing compact, efficient, and highly integrated hydraulic systems. This valve decomposes the functions of traditional directional valves into a modular combination of "cartridge (power level) + control cover plate (primary level)". By replacing different functional valve cores or primary control methods, it can flexibly achieve various control logic from simple single-direction cutoff to complex multi-position direction change, especially suitable for industrial and mobile equipment hydraulic systems with strict requirements for space, weight, response speed, and reliability.
A complete threaded cartridge type directional control valve unit is usually composed of the following four parts:
Valve Core: The core moving part, which is divided into two main structures: slide valve type and cone valve type. The slide valve type has strong flow capacity and fast response; the cone valve type has excellent sealing performance, extremely low leakage, and strong anti-contamination ability.
Valve sleeve: A precisely machined valve core guide and sealing seat, forming a precise friction pair that cooperates with the valve core.
Spring: Provides the repositioning or pre-tightening force for the valve core, determining the valve's open/closed state and the opening pressure.
Sealing element: Usually an O-ring, it is used to isolate the various oil ports of the valve and prevent external leakage.
Function: Fixing the insert component, installing the pilot control valve, and communicating the control oil path within the valve block.
Structure: The cover body integrates the pilot oil passage, damping holes (for improving dynamic performance), pressure measurement ports, etc. It serves as a bridge connecting the main stage (plug-in component) and the pilot stage.
Function: A small-diameter valve that controls the movement of the valve core of the cartridge valve. It receives external signals (electric, hydraulic, manual), alters the pressure in the control chamber of the cartridge, and thereby drives the main valve core to move.
Type: Includes electromagnetic directional valves (DC/AC), hydraulic directional valves, manual directional valves, proportional valves, etc.
◦ Function: Acts as the installation base and oil circuit carrier for the entire valve. It is equipped with threaded insertion holes, main oil circuit channels, and control oil circuit channels in accordance with international standards (such as ISO 7368). It integrates multiple cartridge valves and other components together, completely replacing the complex tubular connections.
Its working principle is based on the statics principle of force balance of the valve core. Taking a typical two-way cartridge valve as an example:
• The valve core is mainly subjected to three oil port pressures: the pressure pA of the main oil port A, the pressure pB of the main oil port B, and the pressure pX of the control chamber X. The corresponding effective areas are AA, AB, and AX respectively. At the upper end of the valve core, there is also the action of the spring force Fs.
• Closing condition: When pX * AX + Fs > pA * AA + pB * AB, the valve core is pressed against the valve seat, and the A and B ports are blocked.
• Activation condition: When pX * AX + Fs ≤ pA * AA + pB * AB, the valve core is lifted and the A and B ports are conductive.
By adjusting the pressure pX of the control chamber X through the pilot control valve (such as by connecting it to the oil tank for pressure relief, or to the pressure oil), the opening and closing of the main valve core can be precisely controlled, enabling the switching of the oil circuit's connection and direction. The combination of multiple plug-in valves can form complex three-way, four-way, or even multi-way multi-port directional valves.
| Classification dimension | Main type | Explanation and characteristics |
| According to its core function | check valve | allows the oil to flow freely in one direction and strictly blocks it in the opposite direction. It is commonly used in pressure retention and anti-backflow circuits. |
| hydraulic directional control valve | under the influence of the control oil pressure, allows the oil to flow in the reverse direction. It is used for locking and releasing of the oil cylinder. | |
| Directional valve | controls the switching of the oil circuit connection relationship. Through the combination of multiple plug-in valves, various forms such as two-position two-way, two-position three-way, three-position four-way, and four-position four-way can be achieved, and the selection of neutral functions (such as O, Y, P, M, H types, etc.) is also diverse. | |
| According to the valve core structure | slide valve type | cylindrical valve core that changes the oil circuit connection state through axial sliding. Advantages: Large flow capacity, low pressure loss, and fast response speed. Disadvantages: There is a certain internal leakage. |
| Pilot-operated (including ball valve) | valve cores are conical or steel balls, and they are sealed through conical/spherical surfaces. Advantages: Excellent sealing performance, capable of achieving zero leakage or extremely low leakage, strong anti-pollution ability. Disadvantage: The hydraulic force during opening is relatively large. | |
| According to the number of oil ports | two-way cartridge valve | the two-way cartridge valve is the most basic form, featuring two main oil ports A and B and one control port X. The basic directional function is achieved by controlling the opening and closing of this valve. |
| Three-way/four-way cartridge valves | Three-way/four-way cartridge valves are composed of two or four two-way cartridge valves integrated within a valve block, forming a complete reversing valve with P (pressure), T (return oil), A, and B working oil ports. |
Throughway | NG6 | Traffic | 40L/min |
Rated pressure | 315bar（4570psi） | Valve core type | Two-way two-port (normally closed) |
Control method | Electromagnetic direct-acting type | Response Time | ≤50ms (on), ≤30ms (off) |
Pollution resistance capability | NAS Level 7 (ISO 4406:19/17/14) | Temperature range | -20°C to 80°C (NBR seal) |
• Compact structure, high integration: Directly embedded in the valve block, without the need for additional valve bodies or complex external pipelines, significantly reducing space and weight, and allowing for flexible system layout.
• Large flow capacity with low pressure loss: The flow channel design is simple and direct, capable of handling a large flow rate while maintaining a very low pressure drop, resulting in high system efficiency.
• Quick response, reliable operation: The valve core is lightweight and has a short stroke. Combined with the pilot control, it can change direction rapidly and has excellent dynamic performance.
• Excellent sealing performance: Especially with the conical valve structure, it can achieve nearly zero leakage, making it highly suitable for applications involving pressure retention, locking, and those with strict environmental protection requirements.
• Strong anti-pollution capability: The design of the clearance between the valve core and the valve sleeve, as well as the conical surface sealing method, allows for a relatively high tolerance for the cleanliness of the oil.
• Modularization and Flexibility: The same specification mounting holes can accommodate different functional inserts, facilitating changes, upgrades and maintenance of system functions.
• Maintenance is simple and cost-effective: In case of a malfunction, usually only a single insert component needs to be replaced, without the need to dismantle the entire valve block or system piping. The maintenance downtime is short.
• Construction machinery: Control systems for the working devices (booms and buckets) of excavators, loaders, and cranes, as well as the traveling and steering systems.
• Industrial equipment: Molding, injection and ejection circuits for injection molding machines and hydraulic presses; Hydraulic control systems for metallurgical rolling mills and continuous casting machines.
• Agriculture and material handling machinery: Hydraulic lifting and steering systems for tractors, harvesters, and forklifts.
• Ship and Marine Engineering: Deck machinery (rudder gear, anchor gear, crane), marine platform hydraulic systems.
• Special vehicles and equipment: fire engines, municipal vehicles, mining machinery, stage lifting equipment, etc.
Clearly define whether it is a one-way cutoff, a hydraulic-controlled one-way, or a multi-position directional change. Based on this, select the type of valve core and the combination method.
Pressure: The maximum working pressure of the system must be lower than the rated pressure of the valve, and safety margins should also be considered.
Flow rate: Select the pipe diameter based on the maximum system demand flow rate, and reserve a certain margin (such as 10-20%) to avoid throttling losses.
Choose the type of pilot control valve based on the degree of automation (electromagnetic, hydraulic, manual, proportional control).
The thread specifications and installation dimensions of the valve must perfectly match the standard holes (Cavity) machined on the valve block (such as in accordance with ISO standards).
Select appropriate sealing materials based on the type of hydraulic oil (mineral oil, water ethylene glycol, etc.) and temperature range.
• Before installation: The valve block socket and all oil passages must be thoroughly cleaned, removing any burrs, chips and contaminants. It is recommended that the cleanliness of the oil meet NAS 1638 Grade 8 (or ISO 4406 20/18/15) or higher.
• During installation: Apply clean hydraulic oil on the O-ring for lubrication. Use a torque wrench and tighten the screws crosswise and evenly according to the specified values in the product. Do not exceed the torque limit to avoid deformation of the valve body or damage to the seals. Pay attention to the oil port markings and correctly connect the P, T, A, B and pilot control oil circuits.
• System debugging: Before the first startup, perform a system flushing. Gradually increase the pressure and check for any leaks at all connections. For adjustable models, make the settings adjustments under no pressure or low pressure conditions.
• Daily maintenance: Regularly monitor the oil temperature, quality and cleanliness of the system. Check for any leakage signs on the exterior of the valve body. Replace the hydraulic oil and filter elements according to the maintenance schedule.
• Fault Handling: Common faults include leakage (check the seals and installation torque), sticking (check the cleanliness of the oil and the wear of the valve core), and sluggish response (check the pilot control pressure and the oil circuit). During maintenance, it is essential to carry out the work after completely depressurizing the system and maintaining a clean environment.
