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A hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy to perform linear reciprocating motion (or swing motion). It has a simple structure and reliable operation. When used for reciprocating motion, it eliminates the need for a speed reducer, has no transmission gap, and moves smoothly. Therefore, it is widely used in the hydraulic systems of various machines. The output force of a hydraulic cylinder is proportional to the effective area of the piston and the pressure difference between the two sides. A hydraulic cylinder is basically composed of a cylinder and cylinder head, piston and piston rod, sealing device, buffer device, and exhaust device. Buffer and exhaust devices depend on the specific application; other devices are required.

I. Classification of Hydraulic Cylinders

Hydraulic cylinders have various structures, and their classification methods are also diverse. According to the different movement methods, they can be divided into linear reciprocating motion and rotary swing. According to the water pressure, they can be divided into single-acting and double-acting types. According to the different structures, they can be divided into piston, plunger, multi-stage telescopic, gear rack, etc. According to the different installation methods, they can be divided into lever, ear ring, base, hinge, etc. According to the different pressure levels, they can be divided into 16Mpa, 25Mpa, 31.5Mpa, etc.

1. Piston

A single piston rod hydraulic cylinder has a piston rod on only one end. As shown in the figure, it is a single piston hydraulic cylinder. The inlet and outlet oil areas A and B at both ends can be used for bidirectional movement through pressure oil or return oil, so it is called a double-acting cylinder.

The piston can only perform unidirectional movement; the opposite direction movement is performed by external force. However, its stroke is generally larger than that of a piston hydraulic cylinder.

2. Plunger Style

(1) A plunger hydraulic cylinder is a single-acting hydraulic cylinder that can only move in one direction; the plunger returns due to other external forces or the weight of the plunger itself.

(2) The plunger is only supported by the cylinder liner and does not contact the cylinder liner, so the cylinder liner is easy to process, making it suitable for long-stroke hydraulic cylinders.

(3) The plunger is always under pressure during operation, so it must have sufficient rigidity.

(4) The weight of the plunger is often very large. When placed horizontally, it is prone to sagging due to its own weight. Unilateral wear of the seal and guide rail is conducive to vertical use.

Elasticity

Telescopic hydraulic cylinders have two or more stages of pistons. The extrusion order of the pistons in a telescopic hydraulic cylinder is from large to small, and the no-load contraction order is generally from small to large. Telescopic hydraulic cylinders can achieve a long stroke, but the length is short when contracted, and the structure is relatively compact. This type of hydraulic cylinder is generally used in engineering machinery and agricultural machinery. When more than one piston moves, the output speed and output force will change when each piston moves.

3. Swing

A swing hydraulic cylinder is an actuator that outputs torque and achieves reciprocating motion. There are various forms, such as single blade, double blade, and spiral swing. Blade: The block is fixed to the cylinder, and the blade is connected to the rotor. According to the direction of the incoming oil, the blade will cause the rotor to reciprocate. There are spiral swing types, single spiral swing, and double spiral swing. Currently, double spiral swing is more commonly used. Two spiral pairs convert the linear motion of the piston in the hydraulic cylinder into a composite motion of linear motion and rotation, achieving swing motion. II. Working Principle of Hydraulic Cylinder

A hydraulic cylinder is an actuator in a hydraulic transmission system and is an energy conversion device that converts hydraulic energy into mechanical energy. A hydraulic motor achieves continuous rotary motion, and a hydraulic cylinder achieves reciprocating motion. The structural forms of hydraulic cylinders include piston cylinders, plunger cylinders, swing cylinders. Piston cylinders and plunger cylinders perform reciprocating linear motion, outputting speed and thrust. Swing cylinders perform reciprocating swing motion, outputting angular velocity (speed) and torque.