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What is Differential Hydraulic Cylinder
Equipment that uses the difference in area between the two ends of a hydraulic cylinder for power transmission.
A differential hydraulic cylinder is a type of hydraulic cylinder that utilizes the difference in effective area at both ends of the cylinder for power transmission. A single-piston rod hydraulic cylinder with a differential connection is called a differential hydraulic cylinder. Common types include: piston-type hydraulic cylinders and double-rod piston hydraulic cylinders.
Product Introduction
According to hydraulic engineering textbooks, a single-piston rod hydraulic cylinder with a differential connection is called a differential hydraulic cylinder.
Type Characteristics
Hydraulic cylinders can be classified according to their mode of motion, mode of operation, and structural form. The common types are as follows:
3.1.1 Piston-type Hydraulic Cylinders
Piston-type hydraulic cylinders can be divided into two structural forms: double-rod and single-rod. They can also be installed in two ways: with the cylinder barrel fixed or with the piston rod fixed.
3.1.1.1 Double-rod Piston Hydraulic Cylinder
Differential hydraulic cylinder
The internal differential hydraulic cylinder is an actuator component of a hydraulic transmission system. It consists of a piston and piston rod housed within the cylinder body, with the piston and piston rod forming a stepped, integral, hollow structure.
Internal differential hydraulic cylinder
The internal differential hydraulic cylinder, an actuator of the hydraulic transmission system, features a piston and piston rod housed within the cylinder body. The piston and piston rod have a stepped, integral hollow structure. The piston head contains a hollow space with a built-in conical valve seat and conical valve. The conical valve seat is embedded and fixed within the piston. A differential oil port is provided on the piston, and a guide rod is installed at the rear of the piston rod’s inner cavity. A spool valve is mounted on the guide rod, and a control oil port is located at the lower part of the piston rod. This utility model offers advantages such as significantly shortening the length of the differential pipeline, increasing switching speed, reducing switching time, and increasing impact force. It is suitable for applications requiring high flow rates, high speed, high impact, long distances, and frequent switching.
Type Characteristics
Hydraulic cylinders can be classified according to their mode of movement, mode of operation, and structural form. Common types are as follows:
Piston type
Piston-type hydraulic cylinders can be divided into two structural forms: double-rod and single-rod. They can also be installed in two ways: with the cylinder body fixed or with the piston rod fixed.
Double-rod piston
Double-rod piston hydraulic cylinders have piston rods at both ends of the piston, and are available in two installation forms: fixed cylinder body and fixed piston rod.
Single-rod piston
When pressure oil is supplied simultaneously to both chambers of a single-rod piston cylinder, the effective working area of the rodless chamber is greater than that of the rod chamber. This results in a force acting on the piston to the right that is greater than the force acting to the left, causing the piston to move to the right and the piston rod to extend outwards. Simultaneously, the oil in the rod chamber is squeezed out and flows into the rodless chamber, thus increasing the extension speed of the piston rod. This connection method of a single-rod hydraulic cylinder is called differential connection. In differential connection, the effective working area of the hydraulic cylinder is the cross-sectional area of the piston rod. The working table’s movement speed is greater than when oil is supplied only to the rodless chamber, while the output force is reduced. Differential connection is an effective way to achieve rapid movement without increasing the capacity and power of the hydraulic pump.
Plunger-type Hydraulic Cylinder
The piston-type hydraulic cylinders discussed earlier are widely used, but due to the high precision required in machining the cylinder bore, the manufacturing difficulty increases with longer strokes, leading to higher manufacturing costs. In practical applications, some situations do not require bidirectional control of the hydraulic cylinder. Plunger-type hydraulic cylinders meet this requirement and are a cost-effective option.
A metallurgical hydraulic cylinder of the plunger type consists of a cylinder barrel, plunger, guide bushing, sealing ring, and end cap. The plunger and the inner wall of the cylinder barrel do not come into contact, so the inner bore of the cylinder barrel does not require precision machining, resulting in good manufacturability and low cost. Plunger-type hydraulic cylinders are single-acting; their return stroke requires the assistance of gravity or other external forces such as springs. To achieve bidirectional movement, two plunger-type hydraulic cylinders can be used in pairs. The end face of the plunger is the pressure-bearing surface, and its area determines the output speed and thrust of the plunger cylinder. To ensure sufficient thrust and stability, the plunger is generally thick and heavy. When installed horizontally, it is prone to uneven wear, so plunger cylinders are suitable for vertical installation. To reduce the weight of the plunger, sometimes a hollow plunger is used.
Plunger cylinders have a simple structure and are easy to manufacture. They are often used in applications requiring long strokes, such as large broaching machines and mining hydraulic supports.
Swivel Type
Swivel hydraulic cylinders can achieve reciprocating oscillating motion at angles less than 360°. Because they can directly output torque, they are also called swivel hydraulic motors. There are two main structural forms: single-vane and double-vane.
A single-vane swivel hydraulic cylinder mainly consists of a stator block, cylinder body, oscillating shaft, vane, left and right support plates, and left and right cover plates. The seal between the two working chambers is ensured by frame-shaped seals embedded in the outer edge of the vane and the partition. The stator block is fixed to the cylinder body, and the vane and oscillating shaft are fixed together. When pressure oil is supplied to the two oil ports successively, the vane drives the oscillating shaft to perform reciprocating oscillation.
Single-Vane Type
The oscillation angle of a single-vane swivel hydraulic cylinder generally does not exceed 280º, and the oscillation angle of a double-vane swivel hydraulic cylinder generally does not exceed 150º. When the input pressure and flow rate are constant, the output torque of the oscillating shaft of a double-vane swivel hydraulic cylinder is twice that of a single-vane cylinder with the same parameters, while the angular velocity is half that of the single-vane type.
Swivel cylinders have a compact structure and high output torque, but sealing is difficult. They are generally only used in medium and low-pressure systems for reciprocating oscillation, indexing, or intermittent motion.
Telescopic Type
Telescopic hydraulic cylinders are composed of two (or more) stages of piston cylinders. The main components include the cylinder body, piston, and sleeve piston.
The cylinder body has inlet and outlet ports A and B at both ends. When oil enters through port A and returns through port B, the first-stage piston is pushed to the right. Because the effective working area of the first-stage piston is large, the movement speed is low but the thrust is high. When the first-stage piston reaches its end point, the second-stage piston continues to move to the right under the action of pressure oil. Because its effective working area is small, the movement speed is fast, but the thrust is low. The sleeve piston acts as both the first-stage piston and the cylinder body of the second-stage piston, having a dual function (in multi-stage systems, the piston of the previous stage cylinder is the cylinder liner of the next stage cylinder). If oil enters through port B and returns through port A, the secondary piston will retract to its end position first, and then the primary piston will retract.
The characteristics of a telescopic hydraulic cylinder are: a long extension stroke of the piston rod and a small structural size when retracted, making it suitable for applications such as dump trucks and the telescopic arms of cranes.
Rack and Pinion Piston
A rack and pinion piston cylinder consists of a double-acting piston cylinder with a rack rod and a gear and rack mechanism. The reciprocating motion of the piston is converted into reciprocating rotation of the gear shaft through the rack and gear mechanism. It is widely used in indexing or positioning mechanisms in automated lines and combined machine tools.
Three-Way Valve Controlled Differential Cylinder
Dynamic response simulation calculation of hydraulic control systems has always been a continuously researched area in the hydraulic industry and has wide applications in hydraulic control systems. Since hydraulic power mechanisms are dynamic components, their dynamic characteristics largely determine the performance of the entire hydraulic servo system. Among them, the three-way valve controlled differential hydraulic cylinder is widely used in mechanical-hydraulic position servo systems.
Troubleshooting
After a period of use, hydraulic cylinders often fail due to wear of seals, cylinder bore wear, internal wall scratches, internal wall corrosion, or piston/piston rod scratches. The sealing performance of the hydraulic cylinder, which is the actuating element of hydraulic equipment, directly affects the equipment’s performance. Especially for larger hydraulic cylinders, repairing or replacing damaged components after seal failure is difficult and costly.
Traditional repair methods involve disassembling the damaged parts and sending them out for repair, or using electroplating or overall surface grinding. These methods have long repair cycles and high costs. To address these issues, the latest repair method utilizes polymer composite materials, for on-site repair of scratched surfaces. The material’s excellent adhesion and good compressive strength not only meet the production requirements under the aforementioned working conditions, but also offer a simple and easy operation process, with no heat effects and no limitations on coating thickness. Furthermore, the coating itself possesses superior oil and corrosion resistance and self-lubricating properties, ensuring wear resistance after repair, guaranteeing normal production for the enterprise, and preventing further damage to equipment components.
The specific repair process is as follows:
1. Surface treatment: First, clean and grind the surface. Use degreasing cotton soaked in acetone or anhydrous ethanol to clean the scratched area before grinding. (If grinding is performed directly without prior cleaning, oil stains will penetrate the cylinder, resulting in poor adhesion or even detachment. During grinding, first grind the raised parts of the damaged area below the baseline to prevent further scratching of the piston. Then, use a file to remove oil stains and foreign objects from the scratched grooves. Finally, use a rotary file to roughen the entire scratched surface.) Cleaning and heating/drying: Wipe the ground scratched surface clean with acetone. Then, use a hot air blower or iodine tungsten lamp to dry the moisture and preheat the surface to be repaired, especially when the room temperature is below 15℃.
2. Material preparation: Mix the materials strictly according to the specified ratio and stir evenly until there is no color difference.
3. Material application: Apply the evenly mixed 2211F material to the scratched surface; the first layer should be thin, even, and completely cover the scratched surface to ensure the best adhesion between the material and the metal surface. Then, apply the material to the entire repair area and repeatedly press it to ensure that the material is filled and reaches the required thickness, making it slightly higher than the inner wall surface of the cylinder.
4. Curing: The material requires 24 hours to fully achieve its performance characteristics at 24°C. To save time, the temperature can be increased using a halogen lamp. For every 11°C increase in temperature, the curing time is halved. The optimal curing temperature is 70°C.
5. Surface Finishing: After the material has cured, use a fine grinding stone or scraper to smooth out any material that protrudes from the surface. The application is then complete.
★★★Review of selected articles in our hydraulic cylinder engineering newsletters:
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- Analysis of the causes of the hydraulic cylinder’s self-descent in the hydraulic system and its solution
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