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DF/DFF
MDP Hydraulics
Adopting a unique symmetrical internal structure or integrated reverse-flow valve, allowing the oil to freely flow in both directions, and the filtering performance is not affected by the flow direction. This greatly simplifies the system design, installation and maintenance process, especially suitable for complex hydraulic circuits with frequent direction changes, non-fixed oil flow direction or limited space.
The housing is made of high-strength ductile iron or forged steel, and undergoes precise processing and strict testing, capable of stably withstanding a system working pressure of up to 420 bar (42 MPa), with stronger peak pressure tolerance, fully meeting the strict requirements of modern heavy machinery, presses, injection molding machines, etc. high-pressure systems.
The filter element uses multi-layer glass fiber (such as Processmicron) or metal fiber (such as Chemicron/Betamicron) as the filtering medium. These materials have high porosity, high pollutant-capturing capacity and stable filtration accuracy, can effectively intercept particles as small as 3 μm, 5 μm, 10 μm (absolute accuracy) and provide excellent protection for servo systems and other high-precision components.
Standard or optional mechanical visual or electronic contamination signaling devices are provided. When the filter element gradually becomes clogged and the inlet and outlet differential pressure reaches the preset value (usually 3-5 bar), the signaling device will trigger a visual indication (pop-up button) or an electrical signal output, promptly alerting the operator to replace the filter element to prevent unfiltered oil from entering the system due to premature opening of the bypass valve.
Adopting a screw-in filter bowl structure, filter element replacement does not require special tools, and the operation is simple and quick. Some large-sized models (such as specifications 330 and above) are also equipped with a pressure release device on the drain plug, which can safely release the pressure inside the housing before replacing the filter element, ensuring maintenance safety.
Designed to be compatible with various hydraulic and lubricating media, including:
Mineral-based and synthetic hydraulic oils (HL to HVLP grades)
Lubricating oil (conforming to DIN, API, etc. standards)
Biodegradable solutions (HETG, HEES, HEPG)
Non-flammable hydraulic fluids (HFA, HFB, HFC, HFD)
High water content working fluid (water content > 50%)
• Basic structure: It is mainly composed of the filter cover (head), the screw-in filter bowl (body), high-performance filter element, differential pressure sensor, and optional bypass valve, reverse flow valve, etc.
• Filtration process: No matter which port the oil enters, it will pass through the filter element. The contaminants are retained on the surface or deep within the filter material, and the clean oil flows out from another port.
• Reverse-flow implementation method:
Method One (DFF type): The internal structure of the filter is designed as a symmetrical flow channel, and the filter element itself allows for bidirectional filtration, eliminating the need for additional valves.
Method 2 (Integrated Reverse Flow Valve): Integrate a reverse flow valve within the filter. When the oil flow reverses, this valve automatically closes, preventing the contaminated filter element from backflowing with the oil, protecting the upstream clean side while allowing the oil to pass through the bypass or another channel.
• Safety Protection:
Shunt valve: When the filter element becomes severely clogged and the pressure difference exceeds the set pressure of the shunt valve (such as 6 bar), the valve opens to ensure uninterrupted oil supply to the system, preventing pump suction failure or filter element rupture, but at this time the oil has not passed through the filter.
No bypass valve design: In certain applications where cleanliness standards are extremely high, you can choose the model without a bypass valve. In case of filter blockage, the machine will automatically stop and require replacement of the filter element to ensure absolute filtration performance.
| Filter specifications | |
| Nominal pressure | 420 bar |
| Maximum flow rate | 960 l/min |
| Temperature range | -30°C to+ 100°C(-30°C to -10°C: max. 210 bar) |
| Material of filter head | EN-GJS 400-15 |
| Material of filter bowl | Steel |
| Clogging indicator | |
| Type | VD |
| Pressure setting | 5.0 bar (DFF: 8.0 bar) |
| Bypass (optional) | |
| Cracking pressure | 6.0 bar |
| Miscellaneous | |
| Seal | NBR (= Perbunan) |
| Installation | As inline filter with or without reversibleoil flow |
| Special designs and accessories | Seals in FKM With bypass valve (except for DFF 1500) Oil drain plug up to DF/DFF 280 Element top-removable -type code:3.X(only DF filters 330-1320 |
| Spare parts | See original spare parts list |
| Certificates and approvals | On request |
1. Determine the flow rate: Select the filter based on the maximum working flow of the hydraulic system, and consider the impact of oil viscosity on the filter's flow capacity. Usually, choose a specification with a rated flow slightly larger than the maximum flow of the system.
2. Determine the pressure rating: The highest working pressure of the filter must be higher than the peak pressure that the system may encounter, and leave a safety margin.
3. Determine the filtration accuracy: Determine it based on the most precise components to be protected (such as 1-5 μm for servo valves, 5-10 μm for proportional valves, and 10-20 μm for general valves) and the target cleanliness level of the system.
4. Determine the connection method and installation form: Based on the on-site pipeline layout, choose threaded or flange connection; you can choose pipe installation or manifold (base plate) installation form. The latter can be directly installed on the valve block, saving space.
5. Select additional functions:
A differential pressure sensor must be equipped to achieve predictive maintenance.
For systems that do not allow downtime, it is recommended to choose the models with bypass valves.
For systems with a single and definite direction of oil flow, a less costly one-way filter (DF type) can be chosen.
• Construction machinery: Protection for the hydraulic pump outlets of excavators, cranes and pump trucks.
• Industrial hydraulics: Filtering of the main pressure pipelines of injection molding machines, die-casting machines, hydraulic presses, and machine tools.
• Steel metallurgy: Key valve assemblies in the hydraulic systems of continuous casting machines, rolling mills, and blast furnaces for pre-protection.
• Ship engineering: Hydraulic systems for steering gear, deck machinery, propulsion systems, etc., which operate under high pressure.
• Energy and Power: Wind turbine pitch and yaw systems, hydropower speed regulation systems.
• Test procedure: Filtering of the high-pressure oil source in the hydraulic test bench.
• Installation: Before installation, ensure that the pipeline is clean; connect in the designed direction (although it is reversible, it is recommended to install according to the indicated flow direction to optimize performance); when tightening, use a torque wrench to avoid over-tightening and damaging the seal.
• First startup: After the system is filled with oil, slightly loosen the exhaust on the filter cover first, then tighten it. Start the pump at a low speed and check for any leaks at the connection points.
• Daily Monitoring: Regularly check the status of the differential pressure sensor. If the mechanical indicator pops out or an electrical alarm is triggered, the filter element should be replaced as soon as possible after the system is shut down.
• Filter replacement: Shut down the system and release the pressure; Use a tool to unscrew the filter bowl; Remove the old filter element, clean the inner cavity of the filter bowl; Install the new filter element (pay attention to the position of the sealing ring); Manually tighten the filter bowl to the specified torque.
• Important Notes: The wiring of the electrical transmitter should be carried out when the system is powered off; when dealing with highly water-containing or flammable liquids, it is necessary to confirm the compatibility of the filter material; discarded filter elements should be disposed of in accordance with environmental protection regulations.
A1: The reversible oil flow design means that this filter allows hydraulic oil to flow in from any one port and out from the other port, without the need to distinguish between the traditional "inlet port" and "outlet port". It completely eliminates the risk of the filter failing or the system malfunctioning due to installation in the wrong direction (such as in systems using a mid-position closed directional valve) or when the installation space is limited and the piping is complex. It greatly simplifies the installation and maintenance.
A2: The hydraulic pump is one of the biggest sources of pollution in the system (particles are generated due to wear). Additionally, contaminants from the outside of the system also pass through the pump first. Installing a filter at the pump outlet (pressure pipeline) enables the immediate capture of these contaminants, preventing them from being impacted by the high-pressure oil flow and damaging the downstream precise control valves (such as servo valves, proportional valves), which is the most economical and effective way to protect the system.
A3: The core advantage lies in the combination of "high pressure" and "reversibility":
• High-pressure safety: Utilizing high-strength materials, it can stably withstand pressures of 420 bar or higher, meeting the most demanding heavy-duty applications.
• Installation无忧： Bidirectional filtration design eliminates the risk of incorrect installation orientation.
• Deep Protection: High-precision filters (such as 3μm) can effectively protect expensive and delicate components.
• Maintain intelligence: The differential pressure sensor promptly alerts for filter replacement to prevent bypass contamination.
• Convenient maintenance: The screw-on design makes it easy to replace the filter element quickly and simply.
A4: "Single-stage" refers to a filter where there is only one main filtration unit (filter element) inside. In contrast, "double-stage" or "multi-stage" filters connect different precision filter elements in series to achieve staged filtration. The single-stage filter has a more compact structure and lower cost, and is suitable for most situations where a single high-precision filtration is clearly required.
A5: This means that the housing, seals, and internal structure of this filter have been designed and tested to be able to safely withstand a fluid static pressure of 420 bar (approximately 42 MPa) continuously. When choosing, this rated pressure must be higher than the highest working pressure (including peak pressure) that your hydraulic system may encounter, and it is recommended to leave a 10-20% safety margin.
A6: "Absolute filtration accuracy" refers to the smallest particle size that the filter can completely intercept. For example, a filter element with a nominal absolute accuracy of 3μm means that particles of 3μm or larger will be completely retained. This is more strict and reliable than the nominal method of "nominal filtration accuracy" (indicating a certain percentage of interception rate), and is a key indicator for protecting precision servo components.
A7: It is highly recommended to be standard equipped. It is the "health monitor" for the filter. As the filter element adsorbs contaminants, the oil flow resistance increases, and the pressure difference between the inlet and outlet rises. When the pressure difference reaches the set value (usually 3-5 bar), the sensor will trigger:
• Mechanically: The red indicator button pops out or the display window turns red.
• Electronic type: Outputs a digital signal (normally open/normally closed contacts), which can be connected to PLC or an alarm light.
This indicates that you should replace the filter element before the bypass valve is opened (which allows unfiltered oil to enter the system).
A8: The main considerations are based on three core parameters:
1. Flow rate: The rated flow rate of the filter should be slightly larger than the maximum working flow rate of the system. It should be noted that high-viscosity oil will reduce the actual flow capacity of the filter. When selecting, refer to the flow-rate vs. viscosity curve chart.
2. Pressure: The maximum working pressure of the filter must be higher than the maximum pressure of the system.
3. Precision: Choose based on the requirements of the most precise components you want to protect. For example: servo systems recommend 1-3 μm, proportional systems recommend 5-10 μm, and general valve groups recommend 10-20 μm.
A9: It is compatible with a wide range of hydraulic and lubricating media, including mineral oil, synthetic hydraulic oil (HL-HVLP), biodegradable fluids (HETG/HEES/HEPG), water ethylene glycol (HFC), and high water-based emulsions (HFA), etc. However, when placing an order, it is necessary to specify the type of medium to ensure that the sealing materials (such as FKM fluororubber, NBR nitrile rubber) are compatible.
A10: The optimal installation location is at the outlet of the hydraulic pump, as close to the pump as possible, and upstream of all control valves (especially precision valves). This way, all downstream components can be protected immediately. Ensure there is sufficient space during installation for replacing the filter element.
A11: Multiple filters of the same specification can be installed in parallel to meet the large flow requirement. It is necessary to ensure that the parallel piping design is reasonable to achieve uniform flow distribution.
4. Maintenance and Troubleshooting
A12: There is no fixed schedule. The replacement period depends on the contamination level of the system, the filtration accuracy, and the cleanliness target of the oil. The only scientific basis is the alarm from the pressure differential sensor. When the sensor triggers, it should be replaced as soon as possible. Do not replace it only according to the time interval.
A13:
1. Shut down and depressurize: Shut off the system and operate the reversing valve multiple times to release the pressure in the pipeline. For models with an oil drain plug, you can open the drain plug to release the pressure.
2. Remove the old filter element: Use tools to unscrew the filter bowl and remove the old filter element. Pay attention to receiving any possible oil spill.
3. Clean and inspect: Clean the inner cavity of the filter bowl and check if the seals are intact.
4. Install the new filter element: Apply a small amount of cleaning oil on the sealing ring of the new filter element, insert it into the filter bowl and manually tighten it to the specified torque (avoid over-tightening).
5. Reset and vent: Reset the differential pressure sensor. Start the system and run it at low speed for a few minutes to check for any leaks.
A14: This might indicate:
1. Abnormally severe system contamination: The pump or other components are severely worn out, generating a large amount of contaminants. Oil contamination degree testing is required.
2. Inappropriate filter element selection: The filtration accuracy is too high, and the pollutant absorption capacity is insufficient, not suitable for the current pollution level of the system.
3. Fault of the alarm sensor: The alarm sensor is damaged or the set value is too low.
4. Abnormal oil viscosity: Low oil temperature leads to extremely high viscosity, causing an increase in differential pressure.
A15: Yes, but be cautious. Having a bypass valve is a safety design to prevent the pump from suctioning air when the filter element is completely blocked or the filter element from breaking, ensuring that the system does not stop. However, when using the bypass valve, the oil does not pass through the filter. Without the bypass valve, the system will not be able to work when the filter element is blocked, thus absolutely ensuring the filtering effect. This is suitable for situations where high cleanliness is required and any unfiltered oil must not pass through (such as certain aviation and testing systems). The choice depends on the priority of the system: continuity or cleanliness.
