Determination of Main Dimensions of Hydraulic Cylinders

1. Determine the working pressure

The working pressure of the hydraulic cylinder is mainly determined according to the type of hydraulic equipment. For hydraulic equipment of different purposes, due to different working conditions, the pressure range usually used is also different.

2. Determine the inner diameter of the cylinder barrel and the diameter of the piston rod.

3. Calculate wall thickness and outer diameter

The wall thickness of the hydraulic cylinder generally refers to the thickness of the thinnest part of the cylinder structure, which is calculated by the strength conditions of the hydraulic cylinder.

4. Determine the working stroke

It can be determined according to the actual maximum stroke of the cylinder.

5. Determine cylinder head thickness

6. Determine the minimum guide sleeve length

When the piston rod is fully extended, the distance from the midpoint of the piston bearing surface to the midpoint of the sliding bearing surface of the cylinder head becomes the minimum guide length. If the guide length is too small, the initial deflection of the hydraulic cylinder will increase, affecting the stability of the hydraulic cylinder. Therefore, the design must ensure that there is a certain minimum guide length.

7. Determine cylinder barrel length

The internal length of the hydraulic cylinder barrel should be equal to the sum of the stroke of the piston and the width of the piston. The length of the cylinder barrel should also take into account the thickness of the end caps at both ends. Generally, the length of the cylinder barrel should not be greater than 20 to 30 times the inner diameter.

8. Check calculation of piston rod stability.

Structure Design of Hydraulic Cylinders

After the main dimensions of the hydraulic cylinder are determined, the structural design of each part must be carried out. It mainly includes: the connection structure of the cylinder barrel and the cylinder head, the connection structure of the piston rod and the piston, the piston rod guide part structure, the sealing device, the buffer device, the exhaust device, and the installation and connection structure of the hydraulic cylinder. Due to different working conditions, the structural forms are also different. Choose according to the specific situation when designing.

1. Connection form of cylinder barrel and cylinder head.

The connection form between the end of the cylinder barrel and the cylinder head is related to the working pressure, the barrel material and the working conditions. Common connection forms include flange connection, threaded connection, outer half-ring connection, and inner half-ring connection.

2. The connection structure of the piston rod and the piston.

Divided into integral structure and combined structure. The combined structure is further divided into threaded connection, half ring connection and taper pin connection.

3. The structure of the guide part of the piston rod.

The structure of the guide part of the piston rod includes the structure of the piston rod, the head cap, the guide sleeve, and the sealing, dustproof and locking devices.

The sealing forms at the piston rod are O-shaped, V-shaped, Y-shaped and X-shaped. In order to remove the dust attached to the exposed part of the piston rod, ensure the oil is clean and reduce wear, a dust ring is added to the outside of the head cap. There are commonly used skeleton dust rings and J-shaped rubber seals, and felt rings can also be used to prevent dust.

4. The selection of the seal at the piston and piston rod.

It should be based on the sealing position, the pressure, temperature, and the range of motion speed used. Different types of sealing rings should be selected. The types of sealing rings mainly include O bezel, O-shaped retaining ring, high and low lip Y-ring, Y-ring, Omega type, V type, piston ring and so on.

5. Buffer device of hydraulic cylinder.

When the hydraulic cylinder drives the working parts to move, due to the large mass of the moving parts and the high movement speed, hydraulic shock will occur when the end of the stroke is reached, and even mechanical collision will occur between the piston and the cylinder end cap. In order to prevent this phenomenon, a buffer device is installed at the end of the stroke. Now introduce several commonly used buffer structures.

6. Exhaust device of hydraulic cylinder.

For machine tool hydraulic cylinders and large hydraulic cylinders that require high movement speed stability, exhaust devices, such as exhaust valves, are required.

The structure of the exhaust device takes many forms. It is generally installed at the highest position at both ends of the hydraulic cylinder. Double-acting hydraulic cylinders require two exhaust valves. When the hydraulic cylinder needs to be exhausted, open the corresponding exhaust valve, and the air together with the oil will be discharged out of the cylinder through the gap of the cone and the small hole, and the exhaust valve will be closed until there is no gas during continuous oil discharge.

7. Installation and connection structure of hydraulic cylinder.

It includes the installation structure of the hydraulic cylinder, the connection of the oil inlet and outlet of the hydraulic cylinder.

  • Installation form of hydraulic cylinder. According to different installation positions and work requirements, there are different mounting methods of hydraulic cylinders, such as long bolt mounting, tripod mounting, flange mounting, trunnion mounting and clevis mounting, etc.
  • Determination of the form and size of the hydraulic cylinder inlet and outlet. The inlet and outlet ports of the hydraulic cylinder can be arranged on the end cap or the cylinder. For hydraulic cylinders with fixed piston rods, the inlet and outlet ports can be located at the end of the piston rod. If the hydraulic cylinder does not have a special exhaust device, the inlet and outlet ports should be located at the highest position of the hydraulic cylinder so that the air can be discharged from the hydraulic cylinder first. The form of inlet and outlet is generally connected by screw holes or flanges.