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Hydraulic Cylinder Design Manufacturing-Technical Foundation
1.1 Classification and Structure of Hydraulic Cylinders
1.1.1 Types and Classifications of Hydraulic Cylinders
Hydraulic cylinders, classified by their purpose or task (function or effect), provide mechanical energy to drive linear mechanical motion.
Hydraulic cylinders can be categorized by their operating mode into single-acting and double-acting. A single-acting cylinder is one in which fluid acts on the piston (or piston rod) in only one direction; a double-acting cylinder is one in which fluid force can be applied to the piston in both directions.
Hydraulic cylinders previously defined in various standards include:
- 1. Adjustable-stroke cylinder. A cylinder whose stroke stops can be changed to allow for varying stroke lengths.
- 2. Cushioned cylinder. A cylinder with a cushioning device.
- 3. Cylinder with a non-rotating piston rod. A cylinder that prevents relative rotation between the cylinder body and piston rod.
- 4. Diaphragm cylinder. A cylinder in which fluid pressure acts on a diaphragm to generate mechanical force.
- 5. Differential cylinder. A double-acting cylinder with different effective areas on either side of the piston. Double-acting cylinders in which the ratio of the effective areas on either side of the piston plays a major role in the circuit.
- 6. Double-rod cylinder. A cylinder with two piston rods that move parallel to each other.
- 7. Impact cylinder. A double-acting cylinder with an integral oil reservoir and valve seat that provides rapid acceleration of the piston and piston rod assembly during extension.
- 8. Magnetic piston cylinder. A cylinder with a permanent magnet on the piston that can be used to operate a position sensor along the stroke length.
- 9. Multi-position cylinder. A cylinder with at least two separate positions in addition to a rest position. At least two pistons are mounted on the same axis and move within a common cylinder body that is divided into several individually controlled chambers to allow selection of different positions.
- 10. Multi-rod cylinder. A cylinder with more than one piston rod on different axes.
- 11. Plunger cylinder. A single-acting cylinder with no piston in the cylinder barrel; pressure is applied directly to the piston rod.
- 12. Servo cylinder. (Pneumatic) A cylinder capable of assuming a specific stroke position in response to a variable control signal.
- 13. Single-rod cylinder. A cylinder with a piston rod extending from only one end.
- 14. Tandem cylinder. A cylinder in which at least two pistons on the same piston rod move within separate chambers of the same cylinder.
- 15. Telescopic cylinder. A cylinder in which two or more stages of extension are achieved by sliding one hollow piston rod inside the other.
- 16. Double-rod cylinder. A cylinder in which piston rods extend from both ends of the cylinder body.
- 17. Piston cylinder. A cylinder in which fluid pressure acts on the piston to generate mechanical force.
- 18. Spring-return single-acting cylinder. A single-acting cylinder with a spring return.
- 19. Gravity-acting single-acting cylinder. A single-acting cylinder with a gravity return.
- 20. Duplex cylinder. A device in which two independently controlled cylinders are mechanically connected on the same shaft, capable of achieving three or four positions depending on the operating mode.
- 21. Multi-stage telescopic cylinder. A cylinder with two or more hollow piston rods that are nested together and extend and retract one by one by sliding one inside the other.
- 22. Digital hydraulic cylinder. A hydraulic cylinder whose position, speed, and direction are controlled by electrical pulse signals.
- 23. Servo hydraulic cylinder. Hydraulic cylinders with static and dynamic performance requirements. Combined with internal or external sensors, servo or proportional valves, and controllers, they can create hydraulic control systems with high control accuracy and fast response speed. Static performance indicators include test run, pressure resistance, internal leakage, external leakage, minimum starting pressure, dynamic friction under load, runout, leakage under low pressure, stroke testing, load efficiency, high-temperature testing, and durability. Dynamic performance indicators include step response and frequency response.
- 24. Gas-to-Liquid Converter. A device that transfers power from one medium (gas) to another (liquid) without amplification.
- 25. Intensifier. A component that converts the inlet pressure of a primary fluid into a higher outlet pressure of a secondary fluid.
Hydraulic cylinder mounting methods include:
- ① Cylinder foot mount. This method uses an angled bracket to secure the cylinder.
- ② Cylinder double clevis mount. This method utilizes a U-shaped mounting device through which a pin or bolt passes to achieve an articulated mounting of the cylinder.
- ③ Cylinder earring mount. This method utilizes earring protruding from the cylinder structure through which a pin or bolt passes to achieve an articulated mounting of the cylinder.
- ④ Cylinder front thread mount. This method utilizes a threaded boss coaxial with the cylinder axis at the rod end of the cylinder.
- ⑤ Cylinder hinge mount. This method allows for angular movement of the cylinder.
- ⑥ Cylinder ball joint mount. This method allows for angular displacement of the cylinder in any plane containing its axis (e.g., a spherical bearing in a earring or double earrings mount).
- ⑦ Cylinder tie rod mount. This method utilizes an extension of the tie rod outside and parallel to the cylinder body to mount the cylinder from one or both ends.
- ⑧ Cylinder transverse mount. All mounting methods defined by a plane perpendicular to the cylinder axis.
- ⑨ Cylinder trunnion mounting. A hinged mounting method achieved by a pair of pins or pinholes on either side of the cylinder, perpendicular to the cylinder axis.
Other terms and definitions for traditional cylinder mounting include:
- ① Side mounting. All mounting methods on a surface parallel to the cylinder axis.
- ② Angle bracket mounting. A mounting method in which the cylinder is secured to a bracket at an angle.
- ③ Tapered hole mounting. A mounting method in which the cylinder is secured by means of a tapered hole in the cylinder housing.
- ④ Foot mounting. A mounting method achieved by using a foot that extends beyond the cylinder profile. The foot can be parallel to the cylinder axis.
- ⑤ Horizontal mounting. All mounting methods on a surface perpendicular to the cylinder axis.
- ⑥ Pinhole mounting. A mounting method consisting of a protrusion from the cylinder structure extending beyond the cylinder profile. It is mounted by means of a pin at right angles to the cylinder axis.
- ⑦ Flange mounting. A horizontal mounting method achieved by using a suitable plate or flange on the cylinder housing (usually with appropriate mounting holes).
- ⑧ End thread mounting. Horizontal mounting using an externally threaded boss or internally threaded groove coaxial with the cylinder.
- ⑨ Tie rod mounting. Horizontal mounting using a long screw extension that clamps the cylinder head and barrel.
- ⑩ Rod end thread mounting. Horizontal mounting using the threads on the end of the piston rod.
- ⑪ Articulated mounting. All mounting methods that allow angular movement of the cylinder.
- ⑫ Double earrings mounting. Articulated mounting using a trunnion or pin passing through a U-shaped mounting device.
- ⑬ Pin mounting. Mounting using an extended flange with a pin hole.
- ⑭ Trunnion mounting. Articulated mounting using a pair of pins or pin holes perpendicular to the cylinder axis.
- ⑮ Ball joint mounting. Articulated mounting that can swing in any direction about a hinge point passing through the cylinder axis.Mounting dimensions (type) are basic parameters of hydraulic cylinders and must be specified during cylinder design.
1.1.2. Structural features of hydraulic cylinders
Structural features of hydraulic cylinders
In the first part of the hydraulic cylinder model, the first digit indicates the number of piston rods of the hydraulic cylinder or the number of stages of the telescopic sleeve hydraulic cylinder (the first digit of the single piston rod cylinder is omitted).
Hydraulic cylinders with the same name and main parameters but different structures are represented by Arabic numerals arranged in sequence according to the order of standardization. Generally include:
- ① Cylinder end connection structure.
- ② Piston structure and connection structure.
- ③ Piston rod structure.
- ④ Cylinder head structure.
- ⑤ Cylinder bottom structure.
- ⑥ Guide sleeve structure.
- ⑦ Sealing structure.
- ⑧ Connection and installation structure.
- ⑨ Oil port structure.
- ⑩ Other structures, such as air release, limit, positioning, buffering, and combined transmission, sensing, control, energy conversion and other components, accessories, devices, etc. For hydraulic cylinders, control primarily focuses on the pressure in the working chamber (e.g., rodless and rod-mounted chambers), the speed (including direction) of the movable element (e.g., piston and rod), and the cylinder stroke (e.g., maximum and adjustable stroke) (or including direction). Energy conversion involves gas-to-liquid and electro-hydraulic conversion.
Further structural features may include material and mechanical properties, heat treatment, surface treatment, corrosion protection, and contamination prevention.
