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MDP Hydraulics
The single-acting hydraulic piston cylinder used in backhoe loaders is a hydraulic actuating component specifically designed for the specific functional mechanisms of backhoe loaders. Unlike double-acting cylinders, the single-acting cylinder is driven by hydraulic oil to perform work in only one direction (usually the extension direction), while the return stroke (retraction) relies on external forces such as the weight of the load, the gravity of the mechanical structure, or the elastic force of the built-in spring. This design makes it an ideal choice for the backhoe loader in scenarios such as lifting the bucket, extending and retracting the stabilizing outriggers, and lifting some simple attachments (such as hydraulic compactors), as it offers a streamlined structure and high cost-effectiveness. It perfectly meets the auxiliary functional requirements that only require a single-directional output and do not require precise hydraulic control for the reset process.
The working principle of a single-acting hydraulic cylinder is based on a simple "hydraulic drive - external force reset" logic.
• Extension (working) stroke: When the hydraulic system supplies high-pressure oil to the non-housing chamber (or piston chamber) of the cylinder through a reversing valve, the hydraulic pressure acts on the effective area of the piston (or piston rod), generating a powerful thrust that pushes the piston rod outward, thereby completing lifting, thrusting or supporting actions.
• Retract (Reset) Stroke: When it is necessary for the cylinder to retract, the hydraulic system releases the pressure and the inlet is connected to the oil tank. At this point, there is no hydraulic power to drive the return movement. The retraction of the piston rod is entirely dependent on:
Gravity reset: For instance, when a bulldozer or its attachments are released hydraulically, they will descend due to their own weight.
Spring reset: A reset spring installed either inside or outside the cylinder, which is compressed when the piston rod extends. After the pressure is released, the stored elastic potential energy of the spring pushes the piston rod back.
•External mechanical force: The reset force is provided by other associated mechanisms.
To accommodate the vibration and impact during the off-road operation of the backhoe loader, this oil cylinder adopts a sturdy and durable design.
• Cylinder barrel: It is precisely manufactured using high-strength seamless steel tubes, and its inner wall is treated with honing to ensure smoothness and flatness, thereby reducing friction and wear during the piston movement. Depending on the application, a piston structure can also be used, in which case the processing requirements for the inner hole of the cylinder barrel are lower and the process is simpler.
• Piston and Piston Rod:
• Piston type: The piston is rigidly connected to the piston rod, and a seal is installed on the piston to isolate the rodless chamber. The piston rod is usually treated with quenching and tempering of alloy steel and coated with hard chromium on the surface to enhance wear resistance and corrosion resistance.
• Piston type: Utilizes solid or hollow pistons as the force-bearing and moving components. There is no requirement for a fit between the piston and the inner wall of the cylinder barrel. It is solely guided by a guide sleeve. This type is particularly suitable for vertical or high-stroke lifting applications.
• Reset mechanism:
•Gravity reset type: No additional reset components, the structure is the simplest.
•Spring reset type: Equipped with a high-strength compression spring, it offers stable and reliable reset force. Suitable for horizontal or inclined installations without the assistance of gravity for reset.
• Sealing system: At the piston (or plunger) position, use combined sealing rings (such as Strohring or Groebel rings) to ensure sealing performance under high pressure and prevent internal leakage. The end of the piston rod is equipped with a dust ring to prevent sand and dust from entering and extend the service life of the sealing components.
• Guide sleeve and end cap: The guide sleeve provides stable support for the piston rod or plunger, preventing overload and sticking. The end cap is connected to the cylinder barrel through threads or flanges to ensure the overall structural strength.
• Ultra-simple design and high reliability: Fewer parts, simple structure, fewer failure points, and excellent operational reliability in the auxiliary functions of the backhoe loader.
• Remarkable cost-effectiveness: Compared to double-acting hydraulic cylinders, it eliminates a complete set of return oil circuits, seals, and control valves, resulting in significant reductions in manufacturing costs and maintenance costs. It is the preferred choice for those who value economic benefits.
• Easy installation and maintenance: The oil port usually has only one (shared for both oil inlet and oil return), and the pipeline layout is simple. The modular design makes it easy to replace key sealing components, reducing equipment downtime.
• Strong environmental adaptability: The robust cylinder design and surface treatment can withstand vibrations, impacts and muddy water conditions on the construction site. The sealing material is compatible with a wide temperature range of hydraulic oil.
• Applicable to specific functions: Specifically designed for the mechanisms on backhoe loaders that do not require bidirectional active control, such as the lifting of the bulldozer blade (reducing by its own weight), the extension of the stabilizing legs (reaching by mechanical locking or manual retraction), etc. The function matching is very high.
1. Front bucket lifting mechanism: When the cylinder extends, it lifts the bucket to perform earthmoving and leveling operations; after hydraulic release, the bucket relies on its own weight to descend and reset. This is the most classic application of a single-acting cylinder.
2. Rear stabilizing outriggers (Outriggers): When the cylinder extends, it lowers the outriggers to stabilize the machine for excavation operations; after the operation is completed, it is usually assisted by manually releasing the valve or a simple mechanical device to retract (the retraction force may come from the equipment structure or the operator's assistance).
3. Special attachments drive: Such as hydraulic compacting plates, asphalt cutters, etc., the working of these accessories usually only requires one-way impact or downward pressure, while the upward retraction is accomplished by the equipment structure or springs.
When choosing a single-acting cylinder for your backhoe loader, please confirm the following key parameters:
1. Load and thrust: Calculate the maximum lifting or thrust force required and select the appropriate cylinder diameter and system working pressure accordingly. The thrust formula is F = P × A (P is the pressure and A is the effective area of the piston).
2. Stroke: Determine the stroke based on the maximum distance the mechanism needs to move.
3. Reset method: Clearly define the installation posture (vertical, horizontal or inclined) and whether there are reliable gravity reset conditions. If not, a spring reset type should be selected.
4. Installation interface: Provide the hole spacing at the hinge points on the main unit, the diameter of the pin shaft, and the required oil port specifications to ensure direct installation.
5. Working environment: If there are extreme temperatures or corrosive environments, please specify this to enable the selection of appropriate sealing materials and surface treatment processes.
• Installation: Ensure that the installation support is firmly fixed and the hinge points are well lubricated. Before connecting the oil pipe, clean the oil ports to prevent contaminants from entering the system. For gravity reset type, it is necessary to ensure that the installation angle allows the load to effectively drive the reset.
• Usage: Do not exceed the rated pressure. Avoid allowing the piston rod of the cylinder to bear lateral forces. Regularly check for leaks, scratches on the piston rod surface, or abnormal noises.
• Maintenance:
◦ Daily inspection: Check for any leakage at the piston rod seal and ensure that the dust ring is in good condition.
Regular maintenance: Replace the hydraulic oil and filter elements according to the maintenance schedule of the main unit to keep the oil clean. When storing for a long time, it is recommended to retract the piston rod to its shortest position.
◦ Fault handling: Common issues include "unable to reset" (check if the reset mechanism is stuck or the spring is失效) and "insufficient thrust/rapid descent" (check if the piston seal is worn and causing internal leakage). It is recommended that professional personnel carry out the repair.
This product is designed, manufactured and inspected in strict accordance with relevant national industry standards. All raw materials are sourced from qualified suppliers. Each oil cylinder undergoes rigorous pressure tests and leakage tests before leaving the factory, ensuring reliable performance. We can provide technical solutions and quality documents that meet specific application requirements based on customer needs.
