Hydraulic cylinders can be divided into single-acting and double-acting types according to the hydraulic pressure. Double-acting hydraulic cylinders have two relative effective areas, which can be the same or different, and are installed with two different ports. The hydraulic oil is connected through the “A” or “B” port, and the piston can generate pulling force or pushing force in two stroke directions. Double-acting hydraulic cylinders can be seen in almost all applications.

Double-acting hydraulic cylinders are divided into two categories: single-rod hydraulic cylinders, double-rod hydraulic cylinders and other special cylinders.

1. Single rod (differential) hydraulic cylinder

Most of the hydraulic cylinders in actual use are single-rod hydraulic cylinders with only one piston rod. Single-rod hydraulic cylinders have a piston rod rigidly connected to the piston and smaller in diameter than the piston. The name of the single-rod (differential) hydraulic cylinder comes from the different effective areas on both sides. The ratio of the cross-sectional area of the piston to the annular area is expressed as a coefficient (middle). The maximum value of the transmitted force is determined by the piston area when extended, the annular area when retracted, and the maximum working pressure.

This means that: under the same working pressure, the force when extending is greater than when retracting, and the ratio of the two is medium. Under the same stroke, due to the difference in area, the volume is also different. Therefore, the stroke speed is inversely proportional to the area.

That is to say:

Large cross-sectional area → slow movement speed

Small cross-sectional area → fast movement speed

2. Double rod hydraulic cylinder

The piston of a double-rod hydraulic cylinder has a small diameter piston rod rigidly connected to each end. The maximum output is determined by the same annular area and maximum working pressure at both ends. This means that the same working pressure will produce the same force in both directions. Since the area and stroke length are the same, the volume is equal and the speed is also equal.

In special cases, the piston rods of a double-rod hydraulic cylinder can have different diameters at both ends of the piston. The force and speed of this type of hydraulic cylinder (similar to a differential cylinder), as shown in the figure above, are proportional to the area ratio φ of the two circular rings.

3. Special form of double-acting hydraulic cylinder

1. Double-acting telescopic hydraulic cylinder

When the hydraulic oil enters the hydraulic cylinder from port “A”, the pistons extend in sequence (as shown in the right figure). The lifting pressure is determined by the load size and the effective area. Therefore, the piston with the largest effective area extends first.

Under constant pressure and flow, the initial extension force is the largest and the speed is the smallest, and the last extension force is the smallest and the speed is the highest.

The order of retraction of each stage is determined by the annular area on which the pressure acts and the size of the external load. When the port “B” is connected to the pressure oil, the piston with the largest annular area returns to the starting position first.

Double-acting telescopic hydraulic cylinders can also be used as synchronous telescopic hydraulic cylinders. In this case, the pistons of each stage extend and retract synchronously.

2. Double-acting quick-reset hydraulic cylinder

Quick action: hydraulic oil pushes the piston to move quickly through the “A1” port, and oil needs to be sucked from the “S” port to prevent vacuum formation;

When continuous clamping force is needed, hydraulic oil enters from “A2” and acts on a large area to provide high pressure.

When retracting due to self-weight or external force, oil returns from “A1” and “A2” ports to achieve the effect of rapid retraction

3. Double-acting tandem hydraulic cylinder.

Double-acting tandem hydraulic cylinders are two hydraulic cylinders connected together, with the piston rod of one cylinder passing through the bottom of the other cylinder and connected to the piston. This arrangement adds up the effective areas. Even without increasing the working pressure, it can transmit a large force with a relatively small outer diameter.

Contact: Nancy Zhu, Sales manager, JW GROUP.

Email: nancy@jwgroup.cc

Web: https://jwcylinder.com

Mobile/Whatsapp:+86 15902166721

HYDRAULIC CYLINDER and CNC parts specialist

JW GROUP is an integrated steel product group, products include: hydraulic cylinder, hydraulic cylinder spare parts, drilling forging parts, pneumatic actuator-scotch yoke, CNC machinery parts etc