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Determine the stroke of the hydraulic cylinder and choose the installation method.
01. Select stroke S
Determine the stroke S according to the overall design requirements of the equipment or device system. If the cylinder selection space allows, please select a cylinder with a stroke longer than the actual required stroke to improve the system’s scalability and prevent excessive extension of the cylinder.
The specific determination principles are as follows:
1) Stroke S = actual maximum working stroke Smax + stroke margin △S;
Stroke margin △S = stroke allowance △S1 + stroke allowance △S2 + stroke allowance △S3.
2) Principles for determining stroke allowance △S
Under general conditions, comprehensive consideration should be given to: the stroke allowance △S1 required for the manufacturing error of the system structure installation dimensions, the stroke allowance △S2 that may be required at the stroke start point when the hydraulic cylinder is actually working, and the stroke allowance △S3 that may be required at the end point.
(Note that when the hydraulic cylinder has a buffer function requirement: the size of the stroke allowance △S will have a direct impact on the buffer function, and it is recommended to reduce the stroke allowance △S as much as possible);
3) For hydraulic cylinders with long stroke (exceeding the longest stroke allowed in each series of this product sample) or specific working conditions, the stability of the hydraulic cylinder needs to be checked according to its specific working conditions (load characteristics, installation method, etc.).
4) For hydraulic cylinders with ultra-short stroke (exceeding the shortest stroke allowed by certain installation methods in each series of hydraulic samples), please confirm with the manufacturer if necessary.
02. Select the installation method
The installation method of the oil cylinder refers to the way the oil cylinder is connected to the equipment. After the installation method is determined, the installation size is determined.
Principles for determining installation methods
1) Flange installation
Suitable for fixed installation during the working process of the hydraulic cylinder, and its force and the support center are on the same axis; its installation method can be selected in three positions: end, middle or tail. How to choose depends on whether the main force acting on the load causes compression (push) stress or tensile (pull) stress on the piston rod. Generally, compression (push) stress is installed by tail and middle flanges, and tensile (pull) stress is installed by end and middle flanges. The determination of end, middle or tail flange installation should be determined in combination with the overall structural design requirements of the system and the bending stability of the hydraulic cylinder under long-stroke compression (push) force conditions.
2) Hinge installation
It is divided into tail single (double) earring installation and end, middle or tail ear shaft installation. It is suitable for the working condition that the force of the hydraulic cylinder during operation makes the machine components moved in it move along the same motion plane in a curved path; when driving the machine components to perform angle operation, the force of the torque is proportional to the angle of the lever arm of the machine connecting rod mechanism and the force generated by the hinge installation.
a) Single (double) earring installation at the tail
The single earring installation at the tail is the most commonly used installation method in hinged installation conditions. It is suitable for the piston rod end to move along the same motion plane in a curved path during operation, and the piston rod will move along a path no more than 3° on both sides of an actual motion plane or the single earring installation conditions required by the structural design; at this time, the tail and rod end spherical bearings can be used for installation, but attention should be paid to the pressure load allowed for the spherical bearing installation.
The double earring installation at the tail is suitable for the working condition where the piston rod end moves along the same motion plane in a curved path during operation; it can be used at any angle in the same motion plane. In the long-stroke thrust condition, the lateral load caused by the “folding force” of the cylinder must be fully considered to cause the longitudinal bending of the piston rod.
The middle fixed trunnion installation is the most commonly used installation method for trunnion installation. The position of the trunnion can be arranged to balance the weight of the cylinder body or at any position between the end and the tail to meet the needs of various purposes. The trunnion pin is designed only for shear load and should not bear bending stress. It should be installed with a rigid mounting support seat with the same length as the trunnion and a support bearing. During installation, the support bearing should be as close to the end face of the trunnion shoulder as possible to minimize the bending stress.
c) The tail trunnion installation is similar to the tail double earring installation, and the selection method is the same as above.
d) The end trunnion installation is suitable for hydraulic cylinders with smaller rod diameters than cylinders with hinged supports at the tail or middle positions. The influence of the overhanging weight of the hydraulic cylinder must be considered for cylinders with long stroke end trunnion installation. In order to ensure the effective load bearing of the support bearing, it is recommended that the stroke of the hydraulic cylinder installed in this way be controlled within 5 times the cylinder diameter.
3) Tripod installation
It is suitable for fixed installation during the operation of the hydraulic cylinder. The installation plane is not in the same plane as the central axis of the cylinder. Therefore, when the hydraulic cylinder applies force to the load, the tripod-mounted cylinder will produce a rollover moment. If the hydraulic cylinder is not well fixed to the component on which it is installed or the load is not properly guided, the rollover moment will produce a large lateral load on the piston rod. When choosing this type of installation, the installed component must be well positioned, tightened and the load properly guided. There are two installation options: end and side tripod installation.
03. Precautions during installation and operation
It should be ensured that the load is applied to the center of the cylinder and its direction is along the cylinder direction, otherwise it is prohibited to use.
When the cylinder is used as a jack, other cylinder accessories such as a top cap and a supporting chassis must be used.
The cylinder can be used with eccentric loads, but it should be ensured that the load does not exceed 5% of the total load, otherwise the service life of the cylinder will be shortened.
It is strictly forbidden to disconnect the oil pipe interface of the oil pump when the cylinder is loaded.
Before designing a hydraulic cylinder, the following issues should be considered:
- Try to reduce the size of the hydraulic cylinder as much as possible to make the structure compact.
- Ensure the reciprocating speed and traction force required by the hydraulic cylinder.
- The piston rod is pulled but not compressed to avoid bending deformation.
- Ensure that each part has sufficient strength, rigidity and durability.
- Try to avoid lateral loads on the hydraulic cylinder.
- When the piston rod of a long-stroke hydraulic cylinder is extended, it should be avoided from sagging as much as possible.
- Can eliminate the deflection between the piston, piston rod and guide rail.
- Consider buffering, exhaust and dust prevention measures according to the working conditions and specific conditions of the hydraulic cylinder.
- The hydraulic cylinder cannot be restricted and flexed due to temperature changes. Especially long hydraulic cylinders should pay more attention.
- There should be possible sealing to prevent leakage.
- The structural elements of the hydraulic cylinder should adopt standard series sizes, and try to choose frequently used standard parts.
- Try to keep the cost low, the manufacturing easy and the maintenance convenient.