Classification and working principle of hydraulic cylinders

Hydraulic cylinders are hydraulic actuators that convert hydraulic energy into mechanical energy and perform linear reciprocating motion (or swinging motion). They have a simple structure and reliable operation. When using it to achieve reciprocating motion, the deceleration device can be eliminated, and there is no transmission gap, and the movement is smooth, so it is widely used in the hydraulic systems of various machines. The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference on both sides; the hydraulic cylinder is basically composed of a cylinder barrel and a cylinder head, a piston and a piston rod, a sealing device, a buffer device and an exhaust device. The buffer device and the exhaust device depend on the specific application, and other devices are indispensable.

Classification of hydraulic cylinders

The structural forms of hydraulic cylinders are diverse, and there are also many ways to classify them: according to the movement mode, they can be divided into linear reciprocating motion and rotary swing; according to the liquid pressure, they can be divided into single-acting and double-acting; according to the structural form, they can be divided into piston type, plunger type, multi-stage telescopic sleeve type, gear rack type, etc.; according to the installation form, they can be divided into tie rods, earrings, base feet, hinge shafts, etc.; according to the pressure level, they can be divided into 16Mpa, 25Mpa, 31.5Mpa, etc.

1. Piston type

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

The piston can only move in one direction, and its reverse movement needs to be completed by external force. But its stroke is generally larger than that of a piston hydraulic cylinder.

Piston hydraulic cylinders can be divided into two types of structures: single-rod and double-rod. The fixing methods are cylinder body fixing and piston rod fixing. According to the effect of hydraulic pressure, there are single-acting and double-acting types. In a single-acting hydraulic cylinder, the pressure oil is only supplied to one chamber of the hydraulic cylinder. The cylinder is driven by hydraulic pressure to achieve unidirectional movement, and the reverse direction movement is achieved by external force (such as spring force, deadweight or external load, etc.); while the movement of the piston in two directions of a double-acting hydraulic cylinder is achieved by alternating oil supply to the two chambers and the effect of hydraulic pressure.

2. Plunger type

(1) The plunger type hydraulic cylinder is a single-acting hydraulic cylinder that can only achieve movement in one direction by hydraulic pressure. The return stroke of the plunger depends on other external forces or the weight of the plunger;

(2) The plunger is supported only by the cylinder sleeve and does not contact the cylinder sleeve. In this way, the cylinder sleeve is very easy to process, so it is suitable for making 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 large. When placed horizontally, it is easy to sag due to its own weight, causing unilateral wear of the seal and guide. Therefore, it is more advantageous to use it vertically.

3. Telescopic hydraulic cylinder

The telescopic hydraulic cylinder has two or more pistons. The order of piston extension in the telescopic hydraulic cylinder is from large to small, while the order of no-load retraction is generally from small to large. The telescopic cylinder can achieve a longer stroke, and the length is shorter when retracted, and the structure is more compact. This type of hydraulic cylinder is often used in engineering machinery and agricultural machinery. There are multiple pistons that move once, and the output speed and output force of each piston are variable when it moves successively.

4. Swinging hydraulic cylinder

Swinging hydraulic cylinder is an actuator that outputs torque and realizes reciprocating motion. There are several forms such as single blade, double blade, spiral swing, etc. Blade type: the stator block is fixed on the cylinder body, and the blade and the rotor are connected together. According to the direction of oil inlet, the blade will drive the rotor to swing back and forth. The spiral swing type is divided into single spiral swing and double spiral. Now the double spiral is more commonly used. The linear motion of the piston in the hydraulic cylinder is converted into a composite motion of linear motion and self-rotation by two spiral pairs, thereby realizing swing motion.

Working principle of hydraulic cylinder

The CUSTOM hydraulic cylinder is an actuator in the hydraulic transmission system. It is an energy conversion device that converts hydraulic energy into mechanical energy. The hydraulic motor realizes continuous rotary motion, while the hydraulic cylinder realizes reciprocating motion. The structural types of hydraulic cylinders are piston cylinders, plunger cylinders, and swing cylinders. Piston cylinders and plunger cylinders realize reciprocating linear motion, output speed and thrust, and swing cylinders realize reciprocating swing, output angular velocity (speed) and torque. In addition to being used individually, hydraulic cylinders can also be used in combination of two or more or in combination with other mechanisms to accomplish special functions. Hydraulic cylinders have a simple structure and reliable operation, and are widely used in the hydraulic system of machine tools.