Rexroth direct acting pressure reducing valve ZDR6DB2-4X/75YM

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Rexroth ZDR6DB2-4X/75YM (R900431771) Mechanical actuation stacked pressure reducing valve product full dimensional detailed explanation

In the modern industrial hydraulic system automation operation system, pressure control components are the core basic components that ensure the smooth operation of the entire equipment, accurate load adaptation, and extended component life. The main oil circuit of hydraulic systems often maintains a high working pressure to meet the high load power requirements of the main actuator, while numerous auxiliary circuits, precision actuators, and small power units only need to adapt to low-pressure stable working conditions. Directly connecting high pressure can easily cause a series of problems such as component wear, structural damage, deviation of action accuracy, and ineffective energy loss. As the core valve class in the field of hydraulic pressure regulation, pressure reducing valves play a key role in high-pressure pressure reduction, secondary stabilization, and circuit pressure classification protection. They are the basic components of modular hydraulic valve group integration and multi branch differentiated pressure supply systems. As a globally renowned brand in the field of industrial hydraulics, Bosch ReXROTH has always adhered to the core principles of precision structural design, stable working condition adaptation, long-term reliable operation, and standardized universal integration in the research and development and manufacturing of pressure valves, directional valves, and flow valves. Its ZDR6D series direct acting stacked pressure reducing valves have undergone multiple generations of technological optimization and iteration, becoming a classic series of products for precise pressure reduction and stabilization in small and medium-sized industrial hydraulic circuits. This article provides a detailed analysis of the Rexroth model ZDR6DB2-4X/75YM, material number R900431771, a mechanically actuated pressure reducing valve. From multiple dimensions such as product basic overview, model code analysis, core structure design, working and operating principles, complete technical parameters, material and medium adaptation, advantages of regulating structure, spare parts matching system, installation integration specifications, industry application scenarios, operational advantages, daily operation and maintenance management, and comparison with the same series of products, a comprehensive and detailed product introduction is carried out to fully present the comprehensive value and application advantages of this valve in industrial hydraulic systems. The full text conforms to the popular science display style of the industry website, with rigorous expression and avoids various marketing prohibited and exaggerated vocabulary. The content is detailed and rich.

1、 Overview of Product Fundamentals

Rexroth ZDR6DB2-4X/75YM (material code R900431771) belongs to the REXROTH original ZDR6D product series. It is an industrial hydraulic pressure reducing valve with a nominal size of 6, a direct acting slide valve structure, mechanical external actuation regulation, and a stacked valve plate installation form. It is classified as a hydraulic system pressure control valve. This product focuses on the pressure regulation of secondary circuits in industrial hydraulic systems. It can stably reduce the high-pressure medium in the upstream main oil circuit to a preset pressure value and maintain a constant output pressure, without interference from pressure fluctuations, flow changes, and load condition fluctuations in the main system. With mature structural design, wide adaptability to various working conditions, precision pressure control accuracy, and convenient installation integration characteristics, it is widely applicable to many industrial scenarios such as general machine tools, automated hydraulic equipment, light industrial machinery, fixtures, small hydraulic stations, and precision transmission circuits. It belongs to the high-performance category of general industrial hydraulic pressure valves and is the preferred basic component for secondary pressure zoning regulation in small and medium-sized modular hydraulic valve groups.

From the perspective of product positioning, this valve component is different from ordinary simple pressure regulating valves. It relies on the precision machining technology and mature valve design system of Lishile's original factory, taking into account structural durability, pressure control stability, universal installation, and convenient maintenance. At the same time, it strictly follows the international hydraulic component universal installation standards and can seamlessly integrate into various standardized stacked valve group systems without the need for additional modification of oil pipelines, reducing system integration design costs and on-site construction difficulties. The product is native to the continuous and normalized operation conditions of industrial sites, and can achieve long-term stable operation under conventional industrial environmental temperature and medium conditions. At the same time, it is equipped with original replacement parts to ensure the convenience of equipment maintenance and component replacement in the later stage, fully covering the full life cycle of equipment use needs.

2、 Detailed analysis of model code and material number

Accurate interpretation of valve model codes is the primary prerequisite for hydraulic system selection, valve group matching, spare parts procurement, and working condition adaptation. The complete identification of this product includes two parts: the original factory model and the exclusive material code. Each character and number corresponds to the exclusive structure, function, pressure, adjustment method, and series version information. The disassembly and analysis are as follows:

（1） Complete model: ZDR6DB2-4X/75YM

ZDR: Product category prefix, representing direct acting stacked pressure reducing valve, is the exclusive series code for this series of pressure reducing valves from Rexroth, covering all 6-specification stacked plate direct acting pressure reducing valve products, uniformly belonging to the ZDR product family, with a unified basic structure, installation size, and internal control oil circuit design foundation.

6: The nominal size is DN6, which is the valve diameter specification and corresponds to the ISO international installation standard size system. It is compatible with the universal installation valve plate of the 6th specification stacked valve group and belongs to the small and medium-sized universal diameter, suitable for small and medium flow hydraulic circuit scenarios.

DB: Internal functional structure code, representing the flow direction function of valve P2 inlet side high pressure and P1 outlet side pressure reduction output, that is, the medium flow direction is P2 → P1 pressure reduction regulation. At the same time, it defines the internal pilot oil circuit oil intake position and valve core control logic, which is different from the same series of DA and DP valves with different oil circuit function versions. It is the core functional differentiation identification of this model.

2: Representing the version number of the valve adjustment component, corresponding to the original factory exclusive adjustment part model, matching the specifications of the exclusive adjustment structure and the hexagonal adjustment structure, and designing differentiated adjustment mechanisms for different numbers in the same series.

4X: Product structure series version number, representing the fourth generation structural optimization version of the valve component. This version has been comprehensively optimized in terms of internal valve core accuracy, spring fatigue performance, sealing adaptability, and oil flow design. The structural dimensions, installation hole positions, and external dimensions remain compatible with the series and can be replaced by cross version basic replacements within the same series.

75: The rated preset upper limit pressure value of the valve, in bar, represents the maximum set pressure of 75 bar that the valve is adapted to from the factory benchmark. At the same time, the product supports adjustable pressure ranges within intervals, not a single fixed pressure value.

YM: Exclusive suffix for adjustment method, representing a hexagonal mechanical adjustment structure with a protective cap. The external structure adopts mechanical actuation adjustment, equipped with a dedicated protective cap and an internal hexagonal adjustment screw. After adjustment, the structure protection can be achieved by relying on the protective cap to avoid external force collision, accidental adjustment, dust and impurities entering the adjustment part, ensuring long-term stability and non deviation of the pressure setting value. It is a highly reliable adjustment structure type for industrial sites.

（2） Exclusive Material Number: R900431771

This code is the exclusive material code of Bosch Rexroth, which is used for factory production, factory quality inspection, warehousing and stocking, factory procurement, genuine product traceability, and spare parts matching. Each ZDR6DB2-4X/75YM valve component corresponds to this material code, and the model appearance identification, internal structure, and accessory matching are unified. Procurement, replacement, and stocking are all based on this material number accurately, effectively avoiding the problem of selection mismatch caused by similar appearance and functional version differences of the same model.

3、 Core structure composition and design features

This pressure reducing valve adopts a classic direct acting slide valve integral structure, which is compact in overall structure and highly integrated in parts. It relies on precision machining technology to complete the assembly of various components. The overall structure mainly consists of seven core parts: valve body shell, control slide valve core, compression elastic component, mechanical adjustment mechanism, sealing component, internal control oil circuit, and leakage oil channel. Each structural component plays its own role and cooperates to complete the entire process of pressure reduction, stabilization, and pressure feedback regulation. The structural design takes into account durability, responsiveness, sealing, and maintenance convenience.

Valve body shell: Made of high-strength alloy structural material through integral forging processing, the valve body structure has sufficient rigidity, can withstand long-term impact of internal high-pressure media, and has excellent resistance to deformation and stress fatigue; The surface of the valve body is treated with anti-corrosion protection to adapt to the normal working conditions of industrial sites with high dust and slight moisture; The valve body strictly follows standardized external dimension design, with 4 reserved medium flow oil ports and 2 working switch positions. The internal oil passage is polished smooth to reduce pressure loss along the medium flow path and improve flow efficiency. At the same time, the bottom surface of the valve body installation is matched with ISO universal installation standards, and the valve face position is precise, meeting the requirements of stacked valve plate installation. When multiple valves are stacked, the oil circuit is interconnected without the need for additional external pipelines.

Sliding valve type control valve core: The core pressure regulating moving parts are processed with high-precision wear-resistant alloy material, and the surface of the valve core is subjected to high-precision grinding treatment. With precise clearance control, the action is smooth without jamming, and the pressure feedback response speed is fast. The valve core relies on the bidirectional force balance between internal medium pressure and spring elasticity to achieve displacement control. By changing the internal throttling opening area through its own axial movement, the cross-sectional area of the medium flow is regulated to achieve high pressure reduction and stable output pressure control; Compared to the cone valve structure, the slide valve structure has better flow capacity, operates smoothly under low-speed flow conditions, and has no frequent impact shaking. It is suitable for continuous operation scenarios with small and medium flow rates, and has excellent internal leakage control.

Compression spring component: Built in high-precision constant force compression spring, made of high fatigue special spring steel. It undergoes long-term repeated force deformation without plastic deformation and has minimal attenuation of elastic force. It can provide stable reference elastic force for a long time, corresponding to the pressure setting reference value, and is the core load-bearing component of pressure balance control. The accuracy of spring elasticity directly determines the stability accuracy of secondary output pressure. The original spring of Lishile has undergone fatigue life testing and can meet tens of thousands of pressure cycles to maintain stable elasticity.

Mechanical actuation adjustment mechanism: The core external adjustment structure of the product, corresponding to the model suffix YM, is a hexagonal adjustment structure with a protective cap. Externally equipped with a closed protective cap, it can isolate the influence of external dust, oil stains, and mechanical collisions on the internal adjustment screw, preventing on-site personnel from accidentally changing the pressure setting value; Internally, there is a dedicated hexagonal adjustment screw, which can be rotated and adjusted using a specialized hexagonal tool to precisely adjust the pre tension force of the internal compression spring, thereby setting the target pressure value of the secondary circuit. The adjustment scale corresponds to clear pressure values, and the adjustment process is linear and smooth. Precise pressure adjustment can be achieved with small adjustments. After the adjustment is completed, it is locked and protected, and the pressure value remains stable for a long time. This mechanical actuation method is different from electronic control adjustment and knob adjustment. The structure has no electronic components and does not rely on electrical signals. The pure mechanical structure runs stably without electrical faults and is suitable for working conditions without electronic control matching and pure hydraulic independent circuits.

Sealing system components: The all valve seals are uniformly made of NBR nitrile rubber sealing material, which is compatible with conventional mineral based hydraulic oil and synthetic hydraulic media, and has good elasticity, sealing performance, oil aging resistance, and temperature adaptability. The sealing performance is stable within the conventional working temperature range. The oil ports, valve core clearances, and regulating parts of the valve are tightly sealed, effectively reducing internal and external leakage problems, ensuring system pressure utilization, and avoiding medium leakage and pollution of equipment and on-site environment Bosch Rexroth.

Internal control feedback oil circuit: Built in integrated internal pilot control oil circuit, all pressure feedback signals are taken from the secondary output side oil circuit internally, without the need for external pilot control oil circuit. The integrated design of internal oil taking and pressure feedback simplifies the external oil circuit connection and reduces the need for additional system components; The internal oil channel layout is reasonable, the pressure signal transmission is fast, and the valve core regulation feedback is timely, which can quickly respond to pressure fluctuations on the output side and adjust the valve core opening in real time to complete pressure correction.

Special oil leakage channel: The spring chamber area adopts an independent external oil return design for oil leakage, with a dedicated Y-shaped oil leakage interface. The internal leakage medium is independently led out and returned to the oil tank through a dedicated channel, without mixing into the main working oil circuit, avoiding the interference of back pressure superposition on pressure control accuracy. Structurally, it ensures that the secondary pressure regulation accuracy is not affected by the system return oil back pressure, and improves the pressure stability under all operating conditions.

The overall structural design has significant advantages: high integration of parts, compact overall volume, and stacked installation that saves equipment space; The pure mechanical slide valve structure operates reliably and has no vulnerable or consumable precision weak electrical components; Adjust structural protection *, pressure setting is not easily offset; Internal oil circuit integrated design, with few external pipelines; The machining accuracy of each component is high, and the overall ability to resist wear and interference from working conditions is strong, which is suitable for the continuous operation needs of industry.

4、 Detailed explanation of the entire process of working principle

As a direct acting pressure reducing valve, this valve relies on the principle of bidirectional force balance between the pressure of the medium itself and the spring elasticity to achieve autonomous pressure reduction and stabilization, without the need for external additional power drive. The entire process relies on the energy of the hydraulic medium itself to complete pressure regulation. The medium flows in a fixed direction to P2 high-pressure inlet → valve pressure reduction regulation → P1 low-pressure stable outlet. The complete working process is divided into four stages: initial conduction, pressure stabilization regulation, overpressure relief protection, and steady-state maintenance. The operating logic is clear, and the control action is coherent and precise.

Initial conduction stage

When the equipment is started and the medium is just introduced into the valve, and the pressure on the outlet side of secondary P1 is lower than the preset set pressure value, the internal compression spring is in the initial pre tension and extension state, and the spring force pushes the control slide valve core to the initial fully open position. At this time, the main flow throttling channel inside the valve is open, and the high-pressure hydraulic medium on the upstream P2 side flows directly to the downstream P1 side load circuit through the internal channel of the valve body. The medium flows smoothly without additional throttling pressure loss, meeting the rapid supply demand of the medium in the initial stage of the circuit. At the same time, the real-time pressure on the secondary P1 side is continuously applied to the force bearing end face on the opposite side of the valve core and spring through an internal dedicated control feedback oil circuit, and real-time output pressure data is collected to form a closed-loop pressure feedback system.

Conventional voltage regulation stage

As the downstream circuit medium is filled and the load is gradually established, the pressure on the outlet side of P1 continues to rise. When the output pressure gradually approaches the preset pressure value corresponding to the spring pre tension force, the hydraulic pressure generated by the medium gradually opposes the spring elastic force. When the pressure on the P1 side reaches the preset reference pressure value, the hydraulic pressure at both ends of the valve core and the spring force reach a precise force balance state, and the valve core automatically moves to the stable control working position, automatically reducing the internal flow throttling opening area. By relying on the change in cross-sectional area of the throttling opening, the high-pressure medium on the upstream P2 side is throttled and depressurized, so that the pressure of the medium passing through the valve remains stable at the preset value. No matter how the pressure on the P2 side of the upstream main system fluctuates within the working range or how the internal flow rate changes, the valve core will adjust the size of the throttling opening in real-time with small displacement, dynamically balance the force, and always maintain the constant pressure on the P1 outlet side, achieving precise pressure stabilization function.

Overpressure relief protection stage

If the downstream actuator is affected by external load reaction force, sudden working condition impact and other factors, resulting in an abnormal increase in pressure on the outlet side of P1, exceeding the preset pressure upper limit, the hydraulic pressure on the outlet side will be greater than the reference elastic force of the internal compression spring, continuously pushing the valve core to further displace towards the compression side of the spring. The valve core continues to contract the throttling channel, and at the same time, the edge control port of the valve core opens the pressure relief passage from the inside of the valve body to the oil tank, releasing excess high-pressure medium into the oil tank through a dedicated channel and quickly releasing excess pressure. Until the pressure on the P1 side drops back to the initial set pressure value, the two ends of the valve core regain force balance, the pressure relief path is closed, and the automatic overpressure protection is completed, which not only avoids downstream components from being damaged by overpressure, but also ensures the overall pressure safety of the circuit.

Steady state maintenance phase

Under normal stable operating conditions, the valve core is always in a dynamic equilibrium working position, and the throttle opening maintains an adaptive opening, continuously completing high-pressure pressure reduction and constant pressure output. The internal feedback oil circuit continuously monitors the pressure, adjusts the valve core position in real time, and finely offsets the effects of flow fluctuations and upstream pressure fluctuations. The entire process is autonomously closed-loop controlled without the need for real-time manual intervention, continuously providing stable and compliant pressure medium for downstream low-pressure circuits.

Advantages of overall regulation principle: The direct acting structure has a direct and fast pressure response, no intermediate transmission link of the pilot valve, and minimal pressure regulation lag; Internally closed-loop autonomous regulation, fully automated operation throughout the process; Having dual functions of pressure reduction and secondary overpressure protection, one valve achieves multiple functions of pressure grading, stabilization, and safety protection; Internal control pressure feedback, simple external oil circuit, and strong system adaptability.

5、 Complete technical parameter summary

Based on the original factory data and product specification information of Lishile, integrate all core technical parameters of the ZDR6DB2-4X/75YM (R900431771) valve component, including specifications, pressure, flow rate, installation, medium, structure, weight, interface and other comprehensive data. The parameters are complete and detailed, and can be directly used for system design, selection calculation, valve group matching, and drawing annotation reference:

Product series: ZDR6D series stacked direct acting pressure reducing valve

Original material number: R900431771

Complete model: ZDR6DB2-4X/75YM

Nominal size: DN6

Medium flow function: P2 (high-pressure inlet) → P1 (pressure reducing outlet)

Drive actuation method: pure mechanical external actuation adjustment

Valve structure types: direct acting, slide valve structure pressure reducing valve

Pressure regulation range: 3bar~75bar (range continuously adjustable, rated upper limit set pressure of 75bar, can be accurately regulated to the 3bar low-pressure range, covering the full pressure requirements of industrial conventional low-pressure circuits)

Maximum tolerable working pressure: 350 bar (the maximum accessible pressure of the upstream P2 inlet side main system, the internal structure of the valve body can stably withstand the high-pressure impact, and the structural safety redundancy is sufficient)

Rated maximum flow rate: 50L/min, suitable for conventional flow supply of small and medium-sized hydraulic circuits, can stably cover most small and medium-sized flow conditions such as fixtures, small oil cylinders, precision transmissions, auxiliary oil circuits, etc.

Installation and connection standards: Strictly follow the ISO 4401-03-02-0-05 international hydraulic valve universal installation and connection standards, with a stacked valve plate installation form. It belongs to the CETOP 03 specification universal stacked valve and can be combined with other brands of stacked valves, directional valves, and flow valves to form an integrated valve group.

Number of oil ports: 4 independent working oil ports

Number of job switching positions: 2 valve core job positions (initial fully open position, stable control position)

Sealing material: NBR nitrile rubber seal

Compatible with hydraulic media: With a wide range of media adaptation, it is compatible with HFC flame retardant hydraulic fluid, HL, HLP mineral based hydraulic oil, HLPD, HVLP, HVLPD series of conventional industrial hydraulic oils, as well as conventional biodegradable hydraulic media, covering various media usage scenarios such as general industrial, special fire protection conditions, and precision equipment Bosch Rexroth.

The overall weight of the product is 1.44kg, which is moderate in weight. After stacking and installation, the overall load of the valve group is balanced, and there is no need for additional load-bearing reinforcement design when installing the valve plate.

Adjustment structure: hexagonal mechanical adjustment with protective cap (YM type), mechanical adjustment without electrical components, protective structure*

Oil leakage method: Spring chamber leaks oil, and external independent oil return (Y-shaped oil return) is used to isolate back pressure interference and ensure pressure regulation accuracy

Structure version: 4X generation optimized structure version, compatible with universal dimensions

6、 Original factory supporting spare parts system

Rexroth has established a standardized and exclusive original spare parts matching system for all models of ZDR6 series valves. Vulnerable parts, regulating components, and sealing kits have independent and exclusive material numbers, which can be purchased separately for replacement without the need for overall valve replacement. This significantly reduces the later operation and maintenance costs of the equipment and extends the overall service life of the valves. The corresponding exclusive spare parts for this product are as follows:

Sealing kit: Material number R961000695

This sealing kit is universally compatible with all valve components of the ZDR 6 DA/DB/DP full series -4X version, including all internal and external sealing rings, gaskets, and gap sealing components of the valve components, covering all sealing positions of the valve body oil port, valve core shaft end, regulating mechanism, and oil circuit interface. When the valve operates for a long time with aging seals, slight leakage, and weakened sealing performance, only the entire original sealing kit needs to be replaced to restore the sealing performance. There is no need to replace the entire valve, and it is suitable for universal replacement of the same version in the entire series, with strong universality.

Adjusted part: Material number R900325215

Exclusive adjustment mechanism core accessories, compatible with all models of DR6D series adjustment components, including internal adjustment screws, transmission connectors, and internal elastic connection structural parts. For scenarios such as wear and tear of the adjustment mechanism, deviation of adjustment accuracy, and damage to the internal transmission structure, replacing this adjustment part alone can repair the adjustment function and restore the ability to accurately adjust pressure. The original factory parts have high dimensional matching and assembly does not require secondary processing.

*The original factory spare parts system enables valve maintenance to no longer be limited to overall replacement, with modular spare parts design that balances economy and convenience, meeting the maintenance needs of industrial equipment for long-term continuous operation.

7、 Core comprehensive advantages of the product

Combining structural design, working principle, technical parameters, working condition adaptation, integration characteristics, and operation and maintenance characteristics, comprehensively sorting out the comprehensive advantages of this valve component compared to the same specification and similar universal pressure reducing valves, all based on objective performance statements of the product itself, without exaggerated marketing statements:

Accurate and stable pressure control, adaptive voltage stabilization across the entire area

Relying on the precision force balancing structure of the direct acting slide valve, the full pressure range of 3-75 bar is continuously adjustable, and the pressure setting accuracy is high; Internal closed-loop pressure feedback regulation can autonomously counteract pressure interference caused by upstream main system pressure fluctuations, loop flow changes, and downstream load condition fluctuations, and continuously and stably output preset pressure; At the same time, it comes with an automatic overpressure relief protection function, which automatically releases the secondary circuit pressure when it exceeds the limit, protecting downstream low-pressure precision components and avoiding overpressure wear and structural damage problems.

The pure mechanical structure operates reliably and has a wide range of adaptability to working conditions

The entire process adopts pure mechanical actuation regulation and pure mechanical valve core regulation, without electronic control components, line connections, or dependence on electrical control signals. There are no electrical faults, signal interference, or circuit damage issues, and it can operate stably in industrial environments with high dust, humidity, no power supply, and complex site conditions; At the same time, the medium has a wide range of adaptability, compatible with multiple types of industrial hydraulic oils and flame-retardant hydraulic fluids. The NBR seal has strong adaptability, and the valve body structure has excellent resistance to high-pressure impact and fatigue, with excellent continuous operation stability.

Stacked modular integration, easy installation and space saving

Standard ISO international installation dimensions, exclusive installation form for stacked valve plates, can be directly stacked and installed on hydraulic integrated valve groups. It can be directly stacked and combined with directional valves, throttle valves, check valves and other components of the same specifications. The oil circuit is naturally connected internally, without the need for additional connecting pipelines, welding pipelines, external adapter joints, simplifying the overall pipeline design of the hydraulic system, reducing the space occupied by equipment valve group installation, and lowering the comprehensive cost of system design, processing and assembly. At the same time, on-site installation and disassembly operations are simple, and the construction difficulty is low.

Adjust structural protection *, set pressure for long-term stability

Exclusive YM type protective cap with hexagonal adjustment structure, external protective cap effectively isolates dust, oil stains, and external force collisions, while preventing non personnel from accidentally touching and changing pressure parameters on site; The internal hexagonal screw adjusts linearly and finely, with precise pressure adjustment. After adjustment, the protective structure is closed and locked, and the pressure setting value is not easily offset during long-term operation. There is no need for frequent on-site re inspection and fine adjustment, and it is suitable for low maintenance and long-term fixed pressure working conditions.

Excellent flow performance with low internal losses

Sliding valve type internal flow structure, smooth channel polishing, low medium flow resistance, smooth flow within the rated 50L/min flow range, and low pressure loss along the way; The independent spring chamber leakage oil external return oil design effectively avoids the negative impact of return oil back pressure on pressure regulation accuracy, further improves the pressure stability accuracy under all operating conditions, and enhances the energy utilization efficiency of the hydraulic system.

Original factory quality, mature craftsmanship, and matching spare parts*

Belonging to the mature mass-produced products of the Rexroth ZDR6D series, it has undergone multiple generations of structural optimization, high precision in component processing, strict assembly processes, and comprehensive performance testing before leaving the factory; Equipped with exclusive sealing and original factory spare parts, modular and individual replacement and maintenance, low maintenance costs and short maintenance cycles in the later stage, simple traceability of parts procurement, and a service life higher than that of industry standard valves.

Universal size compatibility, strong replacement adaptability

The 4X version maintains the series universal standards for external dimensions, installation hole positions, and oil interface, and can directly replace old versions of valves with the same specifications and series without the need to modify valve plates and pipelines. It is also compatible with third-party brand overlay valves that meet the same ISO standards in the industry, and has good compatibility for system upgrades and component replacements.

8、 Installation, debugging and usage specifications

（1） Installation foundation requirements

Priority should be given to selecting a dry, dust-free, non corrosive medium, and non violent mechanical vibration installation area for equipment valve groups. The bottom surface of the valve body installation should be kept flat and clean, and impurities, iron filings, and oil residue on the valve plate installation surface should be cleaned before installation to avoid hard impurities entering the interior of the valve body and causing valve core jamming and wear problems.

Strictly follow the installation specifications for stacked valve groups, align the installation holes according to ISO 4401 standard, ensure even and moderate tightening of bolts, and avoid deformation of the valve body under stress; Confirm that the flow direction of the medium corresponds to the direction of the P2 inlet and P1 outlet oil lines, and that the oil line interface is correctly connected to avoid reverse connection that may cause the valve components to fail to regulate pressure properly.

The independent leakage oil Y interface must be separately connected to the hydraulic oil tank through an external pipeline, and cannot be combined with the main return oil pipeline to prevent the interference of internal pressure feedback caused by the accumulation of return oil back pressure, which affects the accuracy of pressure regulation. After all pipeline connections are completed, check the sealing fit to ensure no medium leakage.

（2） Pressure debugging process

The equipment starts without load and the main system runs under low pressure without load. First, empty the air inside the pipeline. After the hydraulic medium circulates stably and there are no bubbles in the pipeline, carry out pressure regulation operations.

Open the external protective cap of the valve adjustment part, use the corresponding hexagonal special adjustment tool, insert the internal adjustment screw, and slowly rotate for adjustment. Rotate clockwise to increase the spring preload and increase the output pressure; Rotate counterclockwise to reduce the preload force, decrease the output pressure, slowly adjust the entire process, and cooperate with the pressure gauge to observe the actual pressure value on the P1 outlet side in real time.

Gradually adjust to the desired target pressure value of the downstream circuit, stop adjusting when the pressure stabilizes without fluctuations, reset the external protective cap, and complete pressure locking. The protective cap can fix the position of the adjustment screw to prevent external force deviation.

After completing the initial debugging, conduct a load test run and observe the stability of the outlet pressure under full load conditions. If there is a slight deviation, adjust and calibrate again until the pressure remains constant under full load conditions.

（3） Basic usage precautions

During operation, the cleanliness of the medium needs to meet the general requirements of industrial hydraulic components. It is recommended that the hydraulic oil filtration accuracy meet the standard, reduce metal debris and impurity particles in the medium, and avoid valve core wear and jamming faults.

The working pressure should not exceed the rated range of the valve component from 3 to 75 bar, the upstream inlet pressure should not exceed 350 bar, the maximum withstand pressure, the flow rate should not exceed 50 L/min, and it should not operate beyond the working conditions and overload.

Daily operation does not require frequent changes to the pressure setting value, and the adjustment protective cap should not be disassembled unless necessary to reduce the risk of impurities entering the adjustment area.

9、 Widely applicable scenarios across multiple industries

Based on the comprehensive performance of precise voltage stabilization, superposition integration, mechanical reliability, and wide adaptability, the ZDR6DB2-4X/75YM pressure reducing valve is suitable for many industrial hydraulic system secondary circuits. It meets the differential pressure supply needs of the main system high pressure and branch circuit low pressure, completes zone pressure regulation, and covers various general industrial equipment scenarios. The specific typical application areas are as follows:

General metal cutting machine equipment

Various types of CNC lathes, machining centers, grinders, milling machines, drilling machines, hydraulic systems, internal hydraulic fixtures, hydraulic clamping mechanisms, auxiliary feeding cylinders, and guide rail lubrication auxiliary circuits are all operating under low-pressure conditions. There is a significant difference in pressure requirements between the high-pressure power oil circuit of the main system and the auxiliary branch. This valve is connected to the hydraulic valve group of the machine tool, which reduces the high pressure of the main system to the low pressure suitable for the fixture, stabilizes the clamping pressure, avoids workpiece damage and fixture damage caused by excessive pressure, and ensures stable clamping force of the fixture, adapting to the continuous processing and production conditions of the machine tool.

Light Industry Automation Machinery Equipment

Packaging machinery, printing machinery, rubber and plastic auxiliary equipment, and automated conveying hydraulic mechanisms require low load and high action accuracy for their actuators. The auxiliary action circuit only requires low-pressure stable power. Valve components can achieve modular embedding integration, streamline valve group structure, stabilize circuit pressure, ensure smooth and accurate equipment clamping, pushing, pressing and other actions, and adapt to the continuous operation needs of automated production lines.

Hydraulic fixtures and specialized jigs

Industrial flexible fixtures, combination fixtures, hydraulic quick fixtures, and fixture clamping systems have moderate flow requirements and stable pressure requirements in the medium and low pressure range. The adjustable range of this valve is 3-75 bar, covering the commonly used pressure range of the fixture, accurately stabilizing the pressure to ensure uniform clamping force. At the same time, the stacked structure is adapted to small integrated hydraulic stations, and the on-site layout is flexible.

Small independent hydraulic station system

The single machine is equipped with a small hydraulic station, and the equipment comes with a micro power unit. The main pump output pressure is high, while the pressure requirements of the end effector small oil cylinder, buffer mechanism, and fine-tuning mechanism are low. Installing this valve component can achieve graded pressure supply in the station, optimize the internal pressure distribution of the hydraulic station, reduce unnecessary energy loss, and protect small actuator components to extend their service life.

Metallurgical light industry auxiliary hydraulic circuit

Metallurgical equipment auxiliary transmission, small press fit machinery, stamping equipment auxiliary buffer circuit, equipment main working mechanism high pressure and high load, side auxiliary buffer, limit, and fine adjustment mechanism low pressure requirements. Through this valve, pressure zoning regulation is completed to avoid the impact of high pressure on auxiliary components in the main system and improve the smooth operation of the entire equipment.

Universal hydraulic mechanical precision transmission circuit

Various types of small hydraulic cylinder drive circuits, damping control circuits, and low-pressure buffer systems are designed for precision transmission scenarios that require stable low-pressure power and resistance to pressure fluctuations. With fast pressure response and constant pressure output characteristics, they ensure smooth transmission actions and no pressure impact shaking.

10、 Daily maintenance and lifespan management

Scientific and standardized daily maintenance can fully utilize the original design service life of valve components, reduce the occurrence of failures, and develop basic operation and maintenance points based on the structural characteristics of valve components. The operations are all routine industrial equipment maintenance operations, without special complex processes:

routine inspection

During the operation of the equipment, conduct regular visual inspections to check for any medium leakage, oil leakage in the sealing parts, or abnormal temperature rise in the valve body; Check if the protective cap of the adjustment part is intact and not loose or damaged; Observe the pressure gauge value of the circuit and confirm whether the output pressure is stable at the set value, without any abnormal high or low fluctuations.

Media maintenance management

Maintain the cleanliness of the hydraulic medium to meet the standard, regularly replace the hydraulic oil and pipeline filter elements, and reduce impurities in the medium; Strictly use hydraulic media within the range of valve fittings, do not mix unconventional hydraulic oil arbitrarily, and avoid corrosion of seals and wear of valve cores; Control the working temperature of the medium within a normal and reasonable range to slow down the aging rate of the sealing components.

Regular functional check

During the equipment shutdown maintenance period, perform a no-load re inspection of the set pressure value and check the pressure stability; Test the flexibility of the valve core action, without any jamming or hysteresis phenomenon; Check the sealing status of each oil circuit interface. If there are signs of slight aging of the seal, replace the original R961000695 sealing kit in a timely manner.

Maintenance of structural components

The regulating mechanism only opens the protective cap when pressure needs to be adjusted, and remains closed for the rest of the time; Do not disassemble the internal valve core and spring structure of the valve body in a non faulty state to prevent damage to the internal precision fit clearance and the entry of impurities; If there is any adjustment lag or accuracy deviation in the adjustment mechanism, replace the original R900325215 adjustment part to repair it.

Long term shutdown storage

When the equipment is stopped for a long time, the valve components should be filled with clean hydraulic oil for protection, the internal moisture should be drained, and stored in a dry and ventilated environment to avoid moisture corrosion of the valve body and seals; Clean the installation surface before reactivation, exhaust with no load cycle, and then run with load.

11、 Reference for horizontal comparison of products in the same series

The Rexroth ZDR6D series includes multiple functional versions of valves, including DB, DA, and DP. The diameter is uniformly DN6, and the structural versions are mostly 4X. The basic structure of the stacked installation and direct acting slide valve is consistent, with only differences in oil flow direction, pilot oil extraction, and functional differences. Combined with the ZDR6DB2-4X/75YM product, a basic comparison is made for easy selection and differentiation:

ZDR6DB model (this product): Flow direction P2 → P1 pressure reduction, pilot oil circuit oil intake logic exclusive design, mechanical actuation adjustment, compatible with independent inlet high pressure and outlet stable voltage universal circuit, with wide versatility.

ZDR6DA model: A-port circuit pressure reducing structure, suitable for exclusive pressure regulation of A oil circuit. Some versions have built-in one-way reverse flow structure, which is mostly used for two-way oil circuit branch pressure reducing scenarios.

ZDR6DP model: P-port full range pressure reducing structure, internal full control oil intake, stronger overall flow adaptability, higher pressure level upper limit, mostly used for large-scale pressure reduction scenarios in main and branch P oil circuits.

The installation dimensions, sealing kits, and installation standards of the entire series of products are universal, with only differences in internal functions and flow directions. Flexible selection can be made according to the system's oil circuit layout, pressure reduction position, and circuit functional requirements. All spare parts are interchangeable.

12、 Summary

ReXROTH ZDR6DB2-4X/75YM (material number R900431771) is a mature and high-quality component for pressure grading control in industrial hydraulic small and medium-sized circuits, as a classic mechanical actuation stacked pressure reducing valve in the ZDR6D series. The product is based on the core parameters of DN6 standard diameter, direct acting slide valve structure, P2 → P1 exclusive pressure reducing flow direction, adjustable range from 3 to 75 bar, high withstand working pressure of 350 bar, and adapted flow rate of 50 L/min. It relies on multiple advantages such as protective hexagonal mechanical adjustment, ISO standard overlay installation, wide adaptation to multiple media, NBR stable sealing, independent back pressure isolation and oil leakage, and original factory spare parts matching, taking into account pressure control accuracy, structural operation reliability, system integration convenience, and later maintenance economy.

From the perspective of structural design, a stable control system is constructed with precision valve cores, constant force springs, integrated internal control oil circuits, and protective adjustment mechanisms. The pure mechanical structure has no hidden electrical control faults and is suitable for various complex industrial sites; From the perspective of working principle, it independently balances and stabilizes the closed-loop force, and has multiple functions of pressure reduction, constant pressure, and overpressure protection. The entire process is automated without manual intervention; At the application level, it widely covers multiple fields such as machine tools, automation equipment, fixtures, small hydraulic stations, and light industrial machinery to solve the problem of differentiated pressure supply for the main high pressure and branch low pressure of industrial hydraulic systems; From the perspective of the entire lifecycle usage, standardized universal installation size adaptation valve group integration, factory exclusive sealing, and modular replacement of regulating spare parts significantly reduce operation and maintenance costs and extend the overall usage cycle.

In the current industry trend of modular integration, refined pressure control, energy-saving and stable operation, and low-cost operation and maintenance of industrial hydraulic systems, this valve component can fully meet the secondary pressure regulation needs of various general industrial hydraulic equipment with mature and stable original quality, comprehensive and balanced comprehensive performance, and broad and flexible working condition adaptability. It is a highly adaptable basic pressure control component for modular hydraulic valve group integration selection, replacement and upgrading of old valve components, and new system design matching. It provides long-term stable service for various industrial automation hydraulic equipment normal operation scenarios, and continues to provide reliable pressure control guarantee for hydraulic system circuit safety, component protection, and smooth operation.

The content of this article is based on publicly available products and network data. Please refer to the technical manual for actual selection and consider specific operating parameters.

Rexroth direct acting pressure reducing valve ZDR6DB2-4X/75YM