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DFDK
MDP Hydraulics
The online switching type hydraulic pressure filter (also known as dual-switching filter) is a high-pressure pipeline filtration device specially designed for industrial hydraulic systems. Its core design adopts a parallel dual filter element structure and an integrated reversing valve, allowing the liquid flow to be switched from the clogged working filter element to the clean standby filter element through manual or automatic switching, thereby enabling online replacement of the filter elements and ensuring zero interruption of system protection. The product uses industrial standard thread interfaces (such as NPT, BSPP), and is installed firmly and reliably. It is a key safety component for protecting critical precision components such as hydraulic pumps, servo valves, and proportional valves from cntamination and wear, and ensuring the long-term stable operation of the system.
This filter consists of a common housing, two separate filter shells (each containing a filter element), a switching valve, and a differential pressure indicator device.
Hydraulic oil enters from the inlet, and is directed by the switching valve to one of the filter elements for filtration. The clean oil flows through the center tube of the filter element and exits from the outlet.
When the working filter element becomes gradually clogged due to the accumulation of contaminants, causing the pressure difference between the inlet and outlet to increase to the set value, the pressure differential sensor will issue a visual (pop-up indicator rod) or electrical signal alarm. At this point, the operator can operate the switching valve handle to instantly switch the liquid flow path to another clean backup filter element, ensuring no interruption in system pressure and flow. Subsequently, the clogged filter housing can be safely removed in a pressure-free state, and a new filter element can be replaced.
1. Valve body and switching valve: Made of high-strength ductile iron or steel, with a precisely machined reversing valve core inside to ensure smooth switching, reliable sealing, and no internal leakage.
2. Filter housing and filter element: The filter housing can withstand system high pressure; the filter element uses multi-layer composite glass fiber or high-precision stainless steel sintered net, offering various filtration accuracy options ranging from 3μm to 25μm.
3. Differential pressure sensor: Mechanical or electronic type, it monitors the pressure difference before and after the filter element in real time, providing maintenance alerts.
4. Threaded interface: Standard metric or imperial threaded ports, providing reliable metal-to-metal sealing.
Completely resolves the problem of having to stop the machine and release pressure when replacing the filter element in a single-tube filter, achieving maintenance without downtime. This is crucial for continuous production lines such as steel casting, injection molding machines, and presses.
The designed working pressure can reach up to 420 bar or higher, and the shell has undergone strict burst pressure testing.
It offers a wide range of filtration accuracy (βₓ(c) ≥ 200), which can effectively capture worn particles, sealing debris and other contaminants, significantly prolonging the service life of hydraulic components.
Robust structure: The threaded connection offers strong mechanical strength and vibration resistance, suitable for high pulsation and high impact working conditions.
Flexible installation: No need for welding flanges, small installation space requirements, can be directly connected to the existing pipeline system, simplifying system design and renovation.
The pressure differential indicator is clearly visible and easily identifiable by maintenance personnel, allowing them to assess the condition from a distance.
The switching operation is simple (usually only requiring a 90° or 180° rotation of the handle), and the filter housing replacement adopts a quick locking structure, eliminating the need for special tools, significantly reducing the maintenance skill requirements and time.
Utilizes multiple static and dynamic seals such as O-rings and Grooved rings to ensure no leakage under high pressure and temperature variations.
Compatible with common hydraulic media such as mineral-based hydraulic oil, water-ethylene glycol, phosphate esters, and synthetic esters.
This filter is an ideal choice for the following industries and equipment:
• Continuous production processes: steel metallurgy (continuous casting machines, rolling mills), plastic injection molding machines, rubber vulcanization machines, die-casting machines.
• High-precision hydraulic system: CNC machine tools, servo hydraulic system, test bench, simulator.
• Key power systems: Ship steering gear, port cranes, main hydraulic systems of mining machinery.
• As the ultimate protection for the system: Installed after the pump outlet or upstream of critical valve groups (such as servo valves, proportional valves), serving as the last line of defense.
1. System working pressure and flow rate: Select a model with a rated pressure higher than the maximum pressure of the system and a nominal flow rate that meets or exceeds the maximum flow rate of the system.
2. Filtration accuracy: Determine the filtration accuracy based on the sensitivity of the protected component (typically 3-5 μm for servo systems, 10-20 μm for ordinary valves) and the system contamination control target (such as ISO cleanliness grade).
3. Connection size and thread standard: Confirm the pipe interface size (such as 1/2", 3/4", 1") and the thread type (NPT, BSPP, SAE), ensuring a proper match.
4. Medium and temperature: Confirm the type of hydraulic oil and the temperature range of system operation to select the appropriate sealing material.
1. Installation location: It is recommended to install it at the pump outlet, before the directional valve. The arrow direction must be consistent with the oil flow direction.
2. Support: For larger-sized filters, it is advisable to provide appropriate support in the pipeline to reduce the stress on the threaded interface.
3. Exhaust: After installation, slightly loosen the exhaust plug on the filter housing (if any), allow the system to operate under low pressure to expel air, and then tighten it.
1. Initial operation: Check for any leaks at all connections.
2. Daily monitoring: Regularly observe the status of the pressure differential indicator. When the indicator operates or the pressure difference reaches the recommended replacement value (typically 0.35 - 0.5 MPa), prepare for the switch.
3. Switching operation: While the system is running, smoothly rotate the handle of the switching valve to another position. Confirm that the switching is completed, and then replace the blocked filter element.
4. Filter element replacement: Close the stop valve of the filter housing (if any), release the residual pressure in the filter housing, and then remove and replace it. Pay attention to cleaning the sealing surface, and apply a small amount of clean hydraulic oil on the sealing ring before installing the new filter element.
5. Regular inspection: Regularly inspect the appearance of the entire filter and the tightness of the connections.
| Item | Specification |
|---|---|
| Filter Type | Change-over (duplex) high-pressure inline filter |
| Nominal Pressure | 160 bar (DFDK type code 3.X) / 315 bar (DFDK type code 1.X & 2.X) |
| Fatigue Strength | 10⁶ pressure cycles from 0 to nominal pressure |
| Temperature Range | –10 °C to +100 °C (–30 °C to –10 °C: pmax 157.5 bar) |
| Filter Head Material | EN-GJS-400-15 |
| Filter Bowl Material | Steel |
| Change-Over System | Ball change-over valve (T-configuration optional) |
| Filter Bowl Design | Two-piece bowl (standard for DFDK 990–3690; optional for DFDK 660) |
| Filter Element Standards | ISO 2941, 2942, 2943, 3724, 3968, 11170, 16889 |
| Seals | NBR (Perbunan) |
| Clogging Indicator Type | VD differential pressure indicator (up to 420 bar operating pressure) |
| Indicator Pressure Setting | 8 bar (other settings on request) |
| Installation | Inline installation |
| Pressure Equalization | Pressure equalization line (DFDK 330 and above; optional for DFDK 160–280) |
Change-Over Duplex Design
Allows continuous filtration during element replacement, eliminating system downtime and ensuring uninterrupted operation in critical applications.
High-Pressure Pipeline Protection
Designed for high-pressure hydraulic circuits, effectively removing contaminants and extending the service life of pumps, valves, and actuators.
OEM-Compatible Replacement Solution
Form-fit-function compatible with Hydac DFDK and FMND series filters, simplifying maintenance and reducing replacement costs.
High Dirt-Holding Capacity
Advanced filter elements capture more contaminants, reducing replacement frequency and lowering overall maintenance expenses.
Robust Industrial Construction
Heavy-duty housing withstands harsh operating conditions, vibration, and pressure fluctuations in demanding industrial environments.
Optional Monitoring & Indicators
Supports differential pressure indicators for timely maintenance, helping prevent filter blockage and system damage.
Hydraulic Power Units: Continuous oil filtration for centralized hydraulic systems
Steel & Metallurgy Plants: High-pressure filtration in rolling mills and processing lines
Construction Machinery: Protection for pumps and valves in excavators and loaders
Oil & Gas Systems: Reliable filtration under high pressure and continuous operation
Marine & Offshore Equipment: Stable filtration in harsh and corrosive environments
The online switching type hydraulic pressure filter (threaded installation) surpasses the single filtering function of traditional filters. It integrates three core values: continuous protection, active maintenance warning, and convenient operation. By eliminating maintenance downtime, it directly improves equipment utilization and production efficiency. Its sturdy threaded installation design ensures long-term reliability in harsh industrial environments. For any hydraulic system designers and equipment managers who pursue the highest system reliability, the longest component lifespan, and the lowest overall maintenance cost, it is no longer an optional accessory but a strategic essential component for ensuring the long-term healthy operation of the "heart" and "nervous system" of the hydraulic system.
A1: The core feature of an online switching filter is its "online maintenance" capability. It consists of two parallel filter element chambers and an integrated switching valve. The differences are as follows:
• Ordinary single-tube filter: When replacing the filter element, the system must be shut down, depressurized, and the machine must be stopped, resulting in production interruption.
• Online switching filter: When the working filter element gets clogged, by operating the switching valve, the oil circuit can be instantly switched to the standby filter element without stopping the system operation or interrupting the hydraulic power. Then, the dirty filter element can be safely replaced. This ensures the continuity of production or equipment operation, which is its greatest value.
A2: It is mainly installed on the critical high-pressure pipelines that require ultimate protection. Typical locations include:
1. Pump outlet: Protects all downstream components and is the most commonly used position.
2. Upstream of the precision valve group: Installed directly before servo valves, proportional valves, or cartridge valves, serving as the final barrier.
3. Return oil pipeline (please confirm the model is applicable): Used to capture particles in the system's return oil. When installing, make sure the oil flow arrow marked on the valve body is consistent with the actual system flow direction.
A3: To ensure performance compatibility, please confirm the following four points:
1. Working pressure and flow rate: The rated pressure of the selected model must be higher than the maximum working pressure of the system, and the nominal flow rate should be equal to or slightly greater than the maximum flow rate of the system.
2. Filter accuracy: Choose according to the requirements of the protected element (such as 3 or 5 microns for servo systems, 10 or 20 microns for conventional systems). The accuracy is determined by the filter element, and the filter housing can be adapted to different accuracy filter elements.
3. Interface size and thread standard: This is the key for physical connection. The pipe thread specification (such as 1" NPT, 3/4" BSPP) and thread type must be clearly defined to ensure a perfect match. Otherwise, installation will be impossible or leakage may occur.
4. Compatibility with the medium: Inform the supplier of your hydraulic oil type (mineral oil, water ethylene glycol, etc.) to ensure compatibility of the sealing material.
A4: The standard switching operation procedure is as follows (please refer to the product manual for details):
1. Observe the alarm: When the differential pressure sensor (mechanical pointer pops out or the electrical signal light is on) indicates that the filter element is clogged and needs to be replaced, prepare for the switch.
2. Operate the switching valve: While the system is running, smoothly and decisively rotate the handle of the switching valve (usually 90° or 180°) to the other position. You will feel a slight change in the oil flow when the switch is made.
3. Confirm the switch: Observe the pressure gauge to confirm that the system pressure remains normal. At this point, the workload is now being taken on by the clean backup filter element.
4. Replace the dirty filter element: Now it is safe to operate. Close the ball valve of the filter housing (if equipped), or slowly loosen the filter housing to release the residual pressure, then remove and replace the new filter element. After replacement, restore it to the backup state.
• Thread seal: Correctly wrap the sealing tape around the threads or apply the appropriate thread sealant (follow the "three firsts and two last" principle, avoiding the first and last two turns), ensuring a tight seal while preventing debris from entering the system.
• Pipeline support: For larger and heavier filters, it is recommended to provide additional support for the pipeline near the inlet and outlet to prevent the entire weight and vibration of the pipeline from being exerted solely on the threaded interface of the filter.
• Cleaning: Before installation, make sure that the pipe ports and the internal surfaces of the filter interfaces are clean, free from welding debris and burrs.
• Tightening: Use the appropriate tools and avoid over-tightening, as this may cause damage to the threads or the housing.
A6: Possible causes include:
• Valve core jamming: The valve core may be slightly stuck due to long-term non-switching of the system or contamination of the oil. You can try gently moving the handle back and forth or operate it a few times without pressure. If it doesn't work, you need to check the cleanliness of the oil.
• Excessive pressure difference: It may be difficult to switch under extremely high pressure difference conditions. The switching operation should be carried out at an early stage when the pressure difference indicator shows a significant value.
• Pressure loss after switching: It could be that the switching valve is not in the correct position, or the internal seal is damaged, causing the high-pressure oil to bypass directly back to the oil tank. You need to check the valve position and confirm.
• Filter element issue: The backup filter element is already clogged or improperly installed, and it fails to pass the required flow rate after switching.
A7: Sealing is crucial for preventing leakage:
1. Inspect the sealing surface: Before replacement, clean the sealing plane where the filter housing and valve body meet, ensuring there are no scratches or remnants of the old sealing ring.
2. Lubricate the sealing ring: Apply a thin layer of clean hydraulic oil to the O-ring of the new filter element, then insert it into the filter housing. This prevents the sealing ring from twisting or being sheared during installation.
3. Manually screw in: First, use your hand to screw the filter housing into the valve body, ensuring the threads are aligned properly to avoid "scratching".
4. Finally, tighten: Use a tool to tighten it to the recommended torque. Over-tightening will damage the threads or crush the sealing ring.
A8: The filter housing itself has a very long lifespan under normal use. The filter element is a consumable item, and its replacement cycle is not fixed. It depends on the rate at which the system becomes contaminated. The only scientific basis for replacement is the pressure difference indicator. When the pressure difference sensor triggers an alarm, it indicates that the filter element is approaching its capacity for absorbing contaminants. It must be switched and replaced according to the plan. It is strictly prohibited to continue operating after the alarm, otherwise it will trigger the bypass valve or cause the filter element to rupture, and the contaminants will directly enter the system.
A9: Yes, but it must be specially noted during the order. The standard type of sealing material is usually nitrile rubber, which is suitable for mineral oil. For media such as water glycol and phosphate esters, special type models equipped with sealing rings made of fluorine rubber or other special materials must be selected. Otherwise, the sealing ring will quickly corrode, expand, and fail, resulting in serious leakage.
