What are the types and characteristics of hydraulic cylinders?

The hydraulic cylinder (oil cylinder) is mainly used to realize the linear reciprocating movement of the mechanism, and it can also realize the swing. Its structure is simple, reliable in work, and widely used. The input of the hydraulic cylinder is the flow and pressure of the liquid, and the output is the speed and force. Both hydraulic cylinders and hydraulic motors are hydraulic actuators, whose function is to convert hydraulic energy into mechanical energy.

Hydraulic cylinders can be single-acting cylinders and double-acting cylinders according to the oil supply direction; according to the structure, they are divided into piston cylinders, plunger cylinders, telescopic sleeve cylinders, and swing hydraulic cylinders; according to the piston rod forms, they are divided into single-piston rod cylinders and double pistons. Rod cylinder.

Piston hydraulic cylinder
Piston hydraulic cylinders can be divided into single rod type and double rod type. The fixing method is fixed by cylinder body and piston rod. There are single acting and double acting according to the action of hydraulic pressure. In a single-acting hydraulic cylinder, the pressure oil is only supplied to one cavity of the hydraulic cylinder. The cylinder can move in one direction by hydraulic pressure, and the movement in the opposite direction is realized by external force (such as spring force, dead weight or external load, etc.); The movement of the piston in the hydraulic cylinder in two directions is completed by the action of hydraulic pressure through alternating oil in the two chambers.

The double piston rod hydraulic cylinder has piston rods at both ends of the piston, which can be divided into two types of installation: cylinder fixing and piston rod fixing.

The piston of a single-piston-rod hydraulic cylinder has a piston rod at only one end, and the bidirectional movement of the piston can obtain different speeds and output forces.
When the two chambers of a single-rod piston cylinder are supplied with pressure oil at the same time, because the effective area of ​​the rodless chamber is greater than that of the rod chamber, the force of the piston to the right is greater than the force to the left, so the piston moves to the right , The piston rod extends outward; at the same time, the oil with the rod cavity is squeezed out to flow into the rodless cavity, thereby accelerating the extension speed of the piston rod. This connection of a single piston rod hydraulic cylinder The method is called differential connection. Differential connection is an effective way to achieve rapid movement without increasing the capacity and power of the hydraulic pump.

Plunger hydraulic cylinder
When the stroke of the piston hydraulic cylinder is long, it is difficult to process, which increases the manufacturing cost. The hydraulic cylinder used in some occasions does not require two-way control, and the plunger hydraulic cylinder is a low-cost hydraulic cylinder that meets the requirements of this use.

The plunger cylinder is composed of a cylinder barrel, a plunger, a guide sleeve, a sealing ring, a gland and other parts. The plunger and the inner wall of the cylinder barrel are not in contact, so the inner hole of the cylinder barrel does not need to be finished, with good manufacturability and low cost. The plunger hydraulic cylinder is single-acting, and its return stroke needs to be completed by its own weight or other external forces such as springs. If you want to achieve two-way movement, you can use two plunger hydraulic cylinders in pairs; in order to reduce the weight of the plunger, sometimes made of hollow plunger.

Swing hydraulic cylinder
The oscillating hydraulic cylinder can realize reciprocating oscillating motion with an angle of less than 360°. Because it can directly output torque, it is also called a oscillating hydraulic motor. There are mainly two structural forms of single-vane type and double-vane type. The single-blade swing hydraulic cylinder is mainly composed of stator block 1, cylinder block 2, swing shaft 3, blade 4, left and right supporting discs, and left and right cover plates. The stator block is fixed on the cylinder, and the blades and the swing shaft are fixedly connected together. When the two oil ports are successively supplied with pressure oil, the blades drive the swing shaft to swing back and forth.

The swing angle of single-blade swing hydraulic cylinders generally does not exceed 280º, and the swing angle of double-blade swing hydraulic cylinders generally does not exceed 150º. When the input pressure and flow are constant, the output torque of the swing shaft of the double-blade swing hydraulic cylinder is twice that of the single-blade swing cylinder with the same parameters, and the swing angular velocity is half of the single-blade swing. The swing cylinder has a compact structure and a large output torque, but it is difficult to seal. It is generally only used for reciprocating swing, indexing or intermittent movement in medium and low pressure systems.

Telescopic hydraulic cylinder
Telescopic hydraulic cylinders have two-stage or multi-stage pistons. In the telescopic hydraulic cylinder, the order of extension of the pistons 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, while the length is shorter when retracted, and the structure is more compact. Such hydraulic cylinders are often used in construction machinery and agricultural machinery. There are multiple pistons that move at one time, and when each piston moves successively, its output speed and output force are both changed. The two ends of the telescopic double-acting cylinder have oil inlet and outlet ports A and B. When oil enters port A and oil returns to port B, first push the first-stage piston to move to the right. When the first-stage piston travels right to the end point, the second-stage piston continues to move to the right under the action of pressure oil.
The features of the telescopic hydraulic cylinder are: the extended stroke of the piston rod is long, the structure size after contraction is small, and it is suitable for the telescopic boom of dump trucks and cranes.

Rack Piston Cylinder
The rack piston cylinder is composed of a double-acting piston cylinder with a rack rod and a rack and pinion mechanism. The reciprocating movement of the piston becomes a reciprocating rotation of a pinion shaft through the rack and pinion mechanism.