Diagnosis and elimination of poor operation of hydraulic cylinders

Diagnosis and elimination of poor operation of hydraulic cylinders

The hydraulic cylinder is an actuating component of the hydraulic system. The occurrence of its operational faults is not only due to the reasons of the hydraulic cylinder itself but also related to the entire system. Therefore, when eliminating operational faults of the hydraulic cylinder, it is necessary to carefully observe the symptoms of the fault, adopt logical reasoning and the method of pushing item by item, and carefully analyze the cause of the fault from the outside to the inside, so as to determine the elimination method and avoid blind disassembly. Among the numerous causes of hydraulic cylinder operation failures, improper installation, use and maintenance are the reasons for their malfunctions. Such issues will not be elaborated on here. This article only conducts a systematic analysis of the common typical operational fault - poor action of the hydraulic cylinder.

Poor operation of hydraulic cylinders is mostly manifested as: the hydraulic cylinder cannot operate, the hydraulic cylinder operates insensitively (with obstruction phenomena), and the hydraulic cylinder moves and crawles, etc.

1. The hydraulic cylinder fails to operate

The phenomenon that a hydraulic cylinder fails to operate often occurs in a newly installed hydraulic cylinder. When troubleshooting this fault, first look for the cause from the outside of the hydraulic cylinder: whether the resistance of the moving parts of the hydraulic cylinder is too large, and whether there is any jamming, wedging or blocking of other components, etc. Whether the oil intake pressure has reached the specified value. After eliminating external factors, further examine the internal causes of the hydraulic cylinder and adopt corresponding elimination methods. The reasons why the hydraulic cylinder fails to act and the solutions are analyzed as follows:

1. The resistance of the moving parts is too great

Exclusion method

1) Eliminate problems such as jamming and wedging existing in the actuator.

2) Improve the conduction and lubrication conditions of moving parts.

2. The oil pressure at the oil inlet is too low to reach the specified value

Exclusion method

1) Check for any leakage in the oil circuit system and eliminate any leakage.

2) Check whether the sealing rings at the piston and piston rod are damaged, aged or loose.

3) Check whether there are any faults with the hydraulic pump and pressure valve.

3. The oil has not entered the hydraulic cylinder

Exclusion method

1) Check whether the oil pipes, oil circuits, especially the hose joints, have been blocked. Check the relevant oil circuits from the cylinder to the pump in sequence and remove the blockages.

2) Check whether the seal between the cone valve and the valve seat of the relief valve is good.

3) Check whether the solenoid valve spring is damaged or whether the electromagnet coil is burned out; Is the oil circuit not switching sensitively?

4. The sliding parts of the hydraulic cylinder itself fit too tightly, and the sealing friction force is too large

Exclusion method

The piston rod and the guide sleeve should be fitted with H8 / f8.

2) Check whether the dimensions of the sealing ring are processed strictly in accordance with the standards.

3) If a V-shaped sealing ring is adopted, the sealing friction force should be adjusted to a moderate level.

5. Due to improper design and manufacturing, when the piston returns after reaching the end, the effective working area of the piston affected by the pressure oil is too small

Exclusion method

Improve the design and remanufacture.

6. The lateral load on the piston rod is too large, especially causing the cylinder to be pulled or seized

Exclusion method

When installing a hydraulic cylinder, it is necessary to ensure that the axis position of the cylinder is consistent with the direction of movement.

2) Ensure that the load on the hydraulic cylinder passes through the cylinder axis as much as possible to avoid eccentricity.

3) When the long hydraulic cylinder rotates horizontally, the piston rod deflates due to its own weight, causing the guide sleeve and piston to be unevenly loaded, resulting in damage to the cylinder head seal and oil leakage, and the piston sleeping inside the cylinder barrel. To address this issue, the following measures can be taken: increase the piston plan, adjust the outer circle of the piston to be processed into a convex shape, so that the piston can self-position and improve the force condition, thereby reducing and avoiding cylinder pulling. The connection between the piston and the piston rod adopts a spherical joint.

7. The back pressure of the hydraulic cylinder is too high

Exclusion method: Reduce back pressure.

One of the key reasons why the hydraulic cylinder fails to operate is that the oil pressure at the oil inlet is too low, that is, the working pressure is insufficient. The main reasons for insufficient working pressure in the hydraulic system are faults in the hydraulic pump, drive motor and pressure regulating valve. Other causes include: clogged oil filter, too small oil passage diameter, and excessively high or low oil viscosity. Excessive air enters the oil. Serious pollution; The pipeline is connected incorrectly. The pressure gauge is damaged, etc.

2. Insensitivity in movement (with obstruction)

The insensitive operation of the hydraulic cylinder is different from the crawling phenomenon of the hydraulic cylinder. This phenomenon refers to the situation where, after the command for the hydraulic cylinder to act is issued, the hydraulic cylinder cannot act immediately and can only act after a short period of time, or it sometimes moves and sometimes stops, showing very irregular operation. The main causes and troubleshooting methods of this malfunction are:

There is air in the hydraulic cylinder

Exclusion method

Exhaust through the exhaust valve

Check whether there is any air intake at the sealing ring of the reciprocating motion part of the piston rod. If so, replace the sealing ring.

2. There are irregular phenomena in the operation of the hydraulic pump, and the pump rotation is blocked or has a slight seizing phenomenon.

Exclusion method

According to the type of hydraulic pump, solutions should be made respectively based on the causes of its faults. For specific methods, please refer to relevant materials.

When a hydraulic cylinder with a buffer device starts in reverse, it often experiences a temporary stop or reverse retraction of the piston.

Exclusion method

The opening of the check valve is too small, resulting in insufficient oil entering the buffer chamber and even vacuum. Therefore, the above-mentioned fault phenomenon will occur at the moment when the buffer plunger leaves the end cover. In this regard, the opening of the check valve should be enlarged.

When the piston moves at a high speed, the steel ball of the check valve follows the oil flow, thus blocking the valve hole and causing the hydraulic cylinder to operate irregularly.

Replace the steel balls with cone valves or valve cores with guide shoulders.

5. The inner layer of the rubber hose peeled off, causing the oil circuit to be intermittently connected and disconnected, resulting in irregular operation of the hydraulic cylinder

Exclusion method

Replace the rubber hose.

6. The hydraulic cylinder bears a certain lateral load

Exclusion method

See the troubleshooting methods for the reason (6) of "The hydraulic cylinder cannot act" in this article.

Three. There is a crawling phenomenon during movement

The crawling phenomenon refers to the intermittent stopping and moving state that occurs during the movement of the hydraulic cylinder. This phenomenon is particularly prone to occur at low speeds and is one of the most significant faults of hydraulic cylinders. The reasons for the crawling phenomenon of the hydraulic cylinder include both factors outside the hydraulic cylinder and those inherent to the hydraulic cylinder itself.

The reasons for the hydraulic cylinder are:

The stiffness of the motion mechanism is too small, forming an elastic system

Elimination method: Appropriately increase the stiffness of the relevant components to reduce elastic deformation.

2. The installation position accuracy of the hydraulic cylinder is poor

Troubleshooting method: Enhance the assembly quality of the hydraulic cylinder.

3. The difference between the static friction coefficient and the dynamic friction coefficient of the relatively moving parts is too large, that is, the change in friction force is too great

Troubleshooting method: Apply a layer of anti-climbing oil (such as molybdenum disulfide lubricating oil) between the relatively moving surfaces and ensure good lubrication conditions.

4. Poor manufacturing and assembly quality of the guide rails increases friction and leads to poor force conditions

Exclusion method: Enhance manufacturing and assembly quality.

The reasons of the hydraulic cylinder itself include:

There is air in the hydraulic cylinder, which causes the working medium to form an elastic body

Troubleshooting method: Fully expel the air, check whether the diameter of the oil suction pipe of the hydraulic pump is too small, and whether the oil suction pipe joint is well sealed to prevent the pump from drawing in air.

2. Excessive sealing friction

Troubleshooting method: The fit between the piston rod and the guide rod should adopt H8 / f8 fit, and the size of the sealing ring should be processed strictly in accordance with the standard. When using V-shaped sealing rings, the sealing friction force should be adjusted to a moderate level.

3. There is severe wear, scratches and seizing on the sliding parts of the hydraulic cylinder

The reasons for these phenomena are:

1) Poor centering of the load and the hydraulic cylinder.

2) Improper installation and adjustment of the installation bracket.

Troubleshooting method: After reassembling the hydraulic cylinder, it should be carefully aligned, and the rigidity of the installation bracket should be good.

3) The lateral load of the hydraulic cylinder is large.

Troubleshooting method: Try to reduce the lateral load or enhance the hydraulic cylinder's capacity to withstand lateral loads.

4) The cylinder barrel or piston assembly expands and deforms under force.

Troubleshooting method: Repair the deformed parts. When the deformation is severe, replace the relevant components.

5) An electrochemical reaction occurs between the cylinder barrel and the piston.

Troubleshooting method: Replace the material with less electrochemical reaction or replace the parts.

6) Poor material quality, prone to wear, scratches and seizing.

Troubleshooting method: Replace the material and carry out appropriate heat treatment or surface treatment.

7) There are many impurities in the oil.

Troubleshooting method: After cleaning the hydraulic system, change the hydraulic oil and the oil filter.

4. The piston rod is bent throughout its entire length or in some local areas

Troubleshooting method: Calibrate the piston rod. For horizontally installed hydraulic cylinders, if the extension length of the piston rod is too long, additional supports should be added.

5. The coaxiality between the inner hole of the cylinder barrel and the guide sleeve is poor, which causes a strange force phenomenon and leads to crawling

Troubleshooting method: Ensure the coaxiality of the two.

6. Poor straightness of the cylinder bore diameter (drum shape, taper, etc.)

Troubleshooting method: Repair by boring and grinding, and then install a piston or add an O-ring rubber oil seal according to the hole diameter of the cylinder barrel after boring and grinding.

7. The nuts at both ends of the piston rod are tightened too much, resulting in poor coaxiality

Troubleshooting method: The nuts at both ends of the piston rod should not be tightened too much. Generally, they can be tightened by hand. It is necessary to ensure that the piston rod is in a natural state.