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Common faults and troubleshooting methods of hydraulic cylinders

  • Time of issue:2021-07-05

Common faults and troubleshooting methods of hydraulic cylinders

(Summary description)There are many types of hydraulic cylinders. According to their structure, they can be divided into three types: piston cylinder, plunger cylinder and swing cylinder; according to different modes of action, they can be divided into two types: single-acting and double-acting.

  • Time of issue:2021-07-05
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1. The role and classification of hydraulic cylinders

There are many types of hydraulic cylinders. According to their structure, they can be divided into three types: piston cylinder, plunger cylinder and swing cylinder; according to different modes of action, they can be divided into two types: single-acting and double-acting.

The single-acting hydraulic pressure makes the piston (or plunger) move in one direction, and the movement in the opposite direction must be realized by external force (such as spring force or dead weight): the double-acting hydraulic cylinder can realize the movement in two directions with hydraulic pressure.

Because the hydraulic cylinder is simple in structure and reliable in operation, in addition to being used alone, it can also be combined with multiple cylinders or levers, connecting rods, rack and pinion, wheel grabs and other mechanisms to complete a certain special function, so the application of hydraulic cylinders is very wide. .

2. Typical structure and composition of hydraulic cylinder

1. Typical structure of hydraulic cylinder

Double acting single piston rod hydraulic cylinder. It is composed of cylinder bottom, cylinder tube, cylinder head, piston, piston rod, guide sleeve, sealing device and other parts. One end of the cylinder tube is welded to the cylinder bottom, the other end of the cylinder head is connected with the cylinder tube by screws, and both ends are provided with oil.口A and B. The piston and the piston rod are connected together by a semi-ring structure composed of a half ring, a stop ring and a spring retainer ring. The piston and cylinder bore are sealed by a pair of new Y94 polyurethane sealing rings. Because there is a certain gap between the piston and the cylinder bore, a wear-resistant ring (also called support ring) made of nylon 1010 is used for directional guidance. The piston rod does not deviate from the center, the outer diameter of the guide sleeve is sealed with an O-ring, and the inner hole is equipped with a Y-shaped sealing ring and a dust ring to prevent oil leakage and dust from being brought into the cylinder. The cylinder is connected to the outside through a slight hole at the end of the rod, and a nylon bushing is provided in the slight hole to resist wear.

2. Composition of hydraulic cylinder

From the typical structure of the hydraulic cylinder described in 1, it can be seen that the basic cylinder barrel and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device are composed of five parts, which are described as follows:

1) Cylinder tube and cylinder head

Generally speaking, the structure of the cylinder barrel and cylinder head is related to the materials used.

2) Piston and piston rod

The piston rod and piston of a short-stroke hydraulic cylinder can be integrated. This is the simplest form, but when the stroke is long, the processing of this integral piston assembly is more troublesome, so the piston and the piston rod are often manufactured separately , And then connected into one.

3) Buffer device

  Hydraulic cylinders are generally equipped with cushioning devices, especially for large, high-speed or demanding hydraulic cylinders. In order to prevent the piston from colliding with the cylinder head at the end of the stroke, causing noise and impact, a cushioning device must be installed.

The working principle of the cushioning device is to use the piston or cylinder to seal part of the oil between the piston and the cylinder head when it goes to the end of the stroke, forcing it to squeeze out of the small holes or slits to produce great resistance, so that The working parts are braked to gradually slow down the speed of movement to prevent the piston and cylinder head from colliding with each other. Common buffer device structures include annular gap type and adjustable orifice area.

4) Sealing device

The leakage of oil in the high pressure chamber of the hydraulic cylinder to the low pressure chamber is called leakage, and the oil in the hydraulic cylinder leaks to the outside. Due to the leakage and external leakage of the hydraulic cylinder, the volumetric efficiency of the hydraulic cylinder is low, which affects the working performance of the hydraulic cylinder. If leakage occurs, corresponding sealing measures must be taken where the hydraulic cylinder needs to be sealed. The parts that need to be sealed in the hydraulic cylinder are: piston, piston rod, end cover, etc.

The basic requirements for the design and selection of the sealing device are: the sealing device should have good sealing performance and can automatically increase with the increase of pressure; the movement resistance of the seal should be small; the sealing device should be oil-resistant, corrosion-resistant, wear-resistant, long-life, and simple to manufacture , Easy to disassemble and assemble.

5) Exhaust device

During the installation process of the hydraulic cylinder or when it is parked for a long time and re-worked, air will penetrate into the hydraulic cylinder and the pipeline system. In order to prevent abnormal phenomena such as crawling, noise and heat generation of the actuator, it is necessary to exhaust the air in the cylinder and the system. Generally, the oil inlet and outlet ports can be set at the highest point of the hydraulic cylinder to take the air away, and an exhaust hole and a special exhaust valve can also be set at the highest point.

The common failures of hydraulic cylinders mainly include crawling, insufficient thrust, slowing of working speed or even stopping.

Generally, crawling occurs at low speeds. The main reason is that the air accumulated in the cylinder is not cleaned. In addition, excessive or uneven mechanical friction can also cause crawling, such as the piston and the piston rod are not concentric, the piston rod is full or partially bent, the straightness of the cylinder hole is poor, the cylinder is drum-shaped or has a large taper, Decreased thinness or roughness in the cylinder, poor installation accuracy of the oil cylinder, over-tightening of the nut at both ends of the piston rod to make it poorly attentive, over-tightening of the oil seal, excessive friction, etc., will cause crawling.

The matching clearance between the piston and the cylinder of the hydraulic cylinder is too large, the O-ring seal is not the correct size, there is no pre-compression, or the high and low pressure chambers are communicated due to wear, bite aging, etc., partial and complete wear of the cylinder, poor linearity, The inner wall is drum-shaped, causing communication between the high and low pressure chambers, too high oil temperature, low oil viscosity, increased leakage, and other reasons, which will reduce the working speed of the cylinder. When the leakage is too large, the working pressure of the cylinder will be insufficient.

The reasons for the insufficient thrust, speed drop, or stoppage of the hydraulic cylinder are: the clearance between the cylinder and the piston is too small, or the O-shaped sealing groove on the piston is not concentric with the piston. When the two ends of the cylinder are sealed with oil, the sealing ring is at K Incorrect, one side compresses too much, making the piston uncomfortable, and the friction resistance is too large; the piston rod is bent or the oil seals at both ends of the piston rod are too tight, which makes the friction lease too large; the oil contains too much impurities, which makes the cylinder piston stuck or Excessive friction, etc. These reasons will not only increase the no-load pressure and reduce the effective traction of the cylinder, but also cause the cylinder to get stuck in severe cases.

The above are the common faults and troubleshooting methods of hydraulic cylinders. If you want to know more related information, you can contact Shenzhen Weishibo Machinery Equipment Co., Ltd.!

Thank you for your attention!

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