With the advancement of modern industry, hydraulic transmission technology has been extensively applied and developed across numerous global industries. These include construction machinery such as loaders, bulldozers, and rollers; lifting equipment like forklifts, belt conveyors, and truck-mounted cranes; construction machinery such as pile drivers, hydraulic jacks, and graders; as well as agricultural machinery, automotive manufacturing, mining equipment, and metallurgical machinery… Hydraulic transmission systems typically consist of four components: power, actuation, control, and auxiliary elements. The hydraulic cylinder, serving as a key actuator in hydraulic systems, achieves linear reciprocating motion or oscillatory motion under 360 degrees. With its simple structure and reliable operation, it converts mechanical energy from prime movers into hydraulic pressure generated by pumps, which then drives loads to perform reciprocating or oscillatory motions under 360 degrees. To fully understand hydraulic cylinders, we must first grasp the following fundamental principles.
Hydraulic cylinder can be divided into four types according to the structure form: piston cylinder, plunger cylinder, oscillating cylinder and special cylinder; according to the rated pressure, it can be divided into high pressure and super high pressure hydraulic cylinder, medium high pressure hydraulic cylinder and medium low pressure hydraulic cylinder…
1. Cylinder Body: As the core component of hydraulic cylinders, the cylinder body forms a sealed chamber with the cylinder head and piston to drive piston movement. There are eight common cylinder body configurations, typically selected based on end cover connection methods. Materials must demonstrate sufficient strength, impact toughness, and good weldability for welded components, with preferred options including 25,45, ZG200-400, and 1Cr18Ni9 steels. The raw material is usually cold-drawn or hot-rolled seamless steel pipes. Standard manufacturing processes include: quenching and tempering (ensuring structural integrity against oil pressure-induced deformation) → honing or boring (achieving required internal dimensions for piston sealing stability during prolonged reciprocation) → turning (meeting full-length dimensional specifications) → drilling (creating oil ports for hydraulic circuit access) → and finally, fitting.
2. Cylinder head: The cylinder head is installed at both ends of the hydraulic cylinder and forms a tight oil chamber with the cylinder barrel. There are usually welding, thread, bolt, key and pull rod and other connection methods, which are generally selected according to working pressure, hydraulic cylinder connection mode, operating environment and other factors.
3. Piston Rod: The piston rod serves as the primary force-transmitting component in hydraulic cylinders, typically constructed from medium carbon steel (e.g., 45# steel). During operation, the rod experiences thrust, tensile forces, or bending moments, requiring robust structural integrity. As it slides within a guide sleeve, proper clearance is essential – excessive tightness increases friction while looseness may cause seizure and uneven wear. This necessitates precise control of surface roughness, straightness, and roundness. The standard manufacturing process for piston rods follows this sequence: rough turning → tempering → semi-finishing turning → quenching → pre-chromium plating grinding → chromium plating → post-chromium grinding → final turning.
4. Piston: As the primary component converting hydraulic energy into mechanical force, the piston’s effective working area directly determines the cylinder’s output force and movement speed. There are multiple connection methods between the piston and piston rod, including clamp-type, bushing-type, and nut-type designs. When no guide ring is used, pistons are made of high-strength cast iron HT200-300 or ductile iron. For systems with guide rings, piston rods are manufactured from premium carbon steel grades 20,35, and 45.
5. Guide Sleeve: The guide sleeve provides guidance and support for the piston rod, requiring high mating precision, low friction resistance, and excellent wear resistance to withstand pressure, bending forces, and impact vibrations. It contains a sealing device to ensure the cylinder barrel’s rod chamber remains sealed, while an outer dust seal prevents contaminants, dust, and moisture from damaging the sealing mechanism. Metal guide sleeves typically use materials with low friction coefficients and good wear resistance, such as bronze, gray cast iron, ductile cast iron, and oxidized cast iron. Non-metal guide sleeves may employ polytetrafluoroethylene (PTFE) or polytetrafluorochloroethylene (PTFE).
6. Buffering Device: When the piston and piston rod are driven by hydraulic force, they generate significant momentum. Upon entering the cylinder’s end cover and base section, this can cause mechanical collisions that produce substantial impact pressure and noise. The buffer device is designed to prevent such collisions. Its working principle involves converting kinetic energy into thermal energy through throttling in the low-pressure chamber of the cylinder (either partially or entirely), which is then dissipated through circulating oil. The buffer device has two structural types: constant throttling area buffers and variable throttling buffers.
The main parameters of hydraulic cylinder include pressure, flow rate, size specification, piston stroke, moving speed, thrust and pull, efficiency and power of hydraulic cylinder.
1. Pressure: Pressure is the force exerted by hydraulic fluid per unit area, calculated as p = F/A (where F represents the load on the piston and A denotes its effective working area). This formula demonstrates that pressure values are determined by the applied load. Within the same piston’s effective working area, higher loads require greater compressive forces to overcome them. In other words, when the piston’s effective working area remains constant, increased hydraulic fluid pressure generates stronger piston forces. The rated pressure commonly referenced refers to the maximum sustained working pressure a hydraulic cylinder can withstand. The pressure classification for hydraulic cylinders based on this rating is shown in the table below: 1. Maximum Allowable Pressure (MAP): The absolute limit pressure a hydraulic cylinder can endure instantaneously; 2. Test Pressure (T): The mandatory test pressure required for quality inspection. Most countries specify these pressures should not exceed 1.5 times the rated pressure.
2. Flow Rate: Flow rate refers to the volume of hydraulic fluid passing through the cylinder’s effective cross-sectional area per unit time. The calculation formula is Q= V/t = vA, where V represents the oil volume consumed during one piston stroke of the hydraulic cylinder, t denotes the duration required for each stroke, v indicates the piston rod’s movement speed, and A stands for the piston’s effective working area.
3. Piston stroke: Piston stroke refers to the distance traveled between the two poles during the reciprocating movement of the piston. Generally, after meeting the stability requirements of the cylinder, the standard stroke similar to it is selected according to the actual working stroke.
4. Piston’s movement speed: the movement speed is the distance that the pressure oil pushes the piston to move per unit time, which can be expressed as v=Q/A.
5. Size and specification: The size and specification mainly include the inner and outer diameter of the cylinder barrel, piston diameter, piston rod diameter and cylinder head size, etc. These sizes are calculated, designed and checked according to the working environment of the hydraulic cylinder, installation form, thrust and pull required, and stroke.
III. Common Issues and Maintenance of Hydraulic Cylinders As essential components and working mechanisms, hydraulic cylinders, like all mechanical equipment, inevitably experience varying degrees of wear, fatigue, corrosion, loosening, aging, deterioration, or even damage to their structural parts during prolonged operation. These issues degrade the hydraulic cylinder’s performance and technical condition, directly leading to malfunctions or failures in the entire hydraulic system. Therefore, addressing and maintaining common operational problems in hydraulic cylinders is crucial for ensuring reliable equipment performance.
IV. Development Trends of Hydraulic Cylinders With the deepening adoption and expanding application fields of hydraulic technology, new demands are continuously emerging regarding hydraulic cylinder performance, structural design, operational scope, manufacturing precision, appearance, material selection, and testing methodologies. These evolving requirements are driving continuous advancements in hydraulic cylinder technology. The prevailing trends are as follows:
1. High pressure, small size. High pressure is an effective way to reduce the radial size and weight of hydraulic cylinder and reduce the volume of the whole hydraulic device.
2. New materials and lightweight. With high pressure, miniaturization, hydraulic cylinder use environment tests, new materials and lightweight has also become one of the solutions.
3. Novel structure and complex. In order to adapt to the expansion of hydraulic cylinder application scope, various novel structures of hydraulic cylinders are constantly emerging, such as self-control hydraulic cylinder, self-locking hydraulic cylinder, steel cable hydraulic cylinder, peristaltic hydraulic cylinder and composite hydraulic cylinder.
4, high performance, multiple varieties.
5, energy saving and corrosion resistance.
Post time: Aug-31-2025