Hydraulic cylinder: A device that efficiently converts hydraulic energy into mechanical energy, capable of performing linear reciprocating motion or swinging motion. Its structure is concise and stable, with reliable working performance. It can achieve smooth reciprocating motion without the need for deceleration devices, and there is no transmission gap, making it suitable for various applications

It occupies an indispensable position in the hydraulic system of class machinery. The output force of a hydraulic cylinder is closely related to the effective area of the piston and the pressure difference on both sides. It is mainly composed of core components such as cylinder barrel, cylinder head, piston, piston rod, sealing device, etc. The buffering and exhaust devices are configured according to the actual usage scenario.

02. Types and structures of hydraulic cylinders

◉ Movement mode and pressure classification

There are various types of hydraulic cylinders, and their classification methods vary depending on their structural forms. Hydraulic cylinders can be divided into linear reciprocating motion and rotary swing motion. According to the hydraulic pressure, hydraulic cylinders can be divided into single acting and double acting types.

Structural form and installation

Specifically, it includes piston type, plunger type, multi-stage telescopic sleeve type, gear rack type, etc. The installation method of hydraulic cylinders can also affect their type, such as rod type, earring type, foot type, hinge type, etc.

◉ Pressure level

In addition, the pressure level of hydraulic cylinders is an important basis for their classification, such as different levels such as 16Mpa, 25Mpa, 31.5Mpa, etc.

◉ Piston type hydraulic cylinder

The characteristic of a single piston rod hydraulic cylinder is that one end is equipped with a piston rod, while a double acting cylinder means that both the inlet and outlet ports A and B can be filled with pressure oil or return oil, thus achieving bidirectional motion. Although the stroke of piston type hydraulic cylinders is usually large, it should be noted that the piston can only move in one direction, and its reverse movement requires external force. When understanding the working principle of piston hydraulic cylinders, we divide them into two structures: single rod and double rod. These structures are combined with the cylinder body fixation and piston rod fixation methods, as well as the single acting and double acting situations of hydraulic pressure. In a single acting hydraulic cylinder, hydraulic force only pushes the cylinder body to move in one direction, while the movement in the opposite direction relies on external forces such as spring force, self weight, or external loads. In contrast, double acting hydraulic cylinders rely entirely on hydraulic pressure to achieve piston movement in two directions by alternately injecting oil into two chambers. A plunger hydraulic cylinder is a single acting hydraulic cylinder whose direction of motion is determined solely by hydraulic pressure. The cylinder liner of this hydraulic cylinder only needs to support the plunger, making it particularly suitable for making long stroke hydraulic cylinders. The telescopic hydraulic cylinder has multi-stage pistons to achieve longer stroke and compact structure.

03. Swing hydraulic cylinder

◉ Basic principles

Swing hydraulic cylinder, as a special actuator, can output torque and achieve reciprocating motion, with various design forms.

◉ Design Form

In a blade type swing hydraulic cylinder, the stator block is firmly fixed to the cylinder body, while the blades are connected to the rotor. By changing the oil inlet direction, the blades will drive the rotor to oscillate back and forth. The spiral swing hydraulic cylinder converts the linear motion of the piston inside the cylinder into compound motion through two spiral pairs, that is, the combination of linear motion and rotational motion, thereby achieving the swing effect. At present, the application of double helix swing hydraulic cylinders is more widespread.

04. Function of buffer device

In hydraulic systems, when a hydraulic cylinder drives a mechanism with a certain mass and moves to the end of its stroke, the piston of the hydraulic cylinder carries a large amount of kinetic energy due to inertia. To effectively mitigate and avoid such hazards, deceleration devices can be added to the hydraulic circuit, or specialized buffering devices can be designed in the cylinder body to reduce mechanical collisions between the piston and cylinder head, avoid impact, noise, and possible damage.