Hydraulic cylinder It is the actuator in a hydraulic system that converts hydraulic energy into mechanical energy. Its malfunctions can generally be categorized as improper operation of the hydraulic cylinder, insufficient force to advance the load, piston slippage, or crawling. Since equipment downtime caused by hydraulic cylinder failures is relatively uncommon, it is essential to pay close attention to troubleshooting and proper maintenance of these components.
 

　　I. Fault Diagnosis and Troubleshooting
 

　　1. Incorrect behavior or behavioral failure

　　The causes and solutions are as follows:

　　(1) The valve spool is stuck, or the valve port is blocked. When the flow control valve or directional valve spool becomes clogged, or when the valve port is obstructed, the hydraulic cylinder may exhibit incorrect operation or fail to operate altogether. In such cases, inspect for oil contamination and determine whether dirt or colloidal deposits are lodged on the valve spool or blocking the valve ports. Also check for wear on the valve body, clean the system filters, flush the reservoir, and replace the hydraulic fluid.

　　(2) The piston rod is jammed in the cylinder or hydraulic cylinder. In this situation, no matter how you operate the system, the hydraulic cylinder will not move, or its movement will be very slight. At this point, check whether the piston and piston‑rod seals are too tight, and inspect for dirt and gelatinous deposits. Also verify that the axis of the piston rod aligns with that of the cylinder, assess the condition of the seals, and determine whether the load is excessive.

　　(3) The hydraulic system’s control pressure is too low. Possible causes include excessive throttling resistance in the control lines, improper adjustment of the flow valve, incorrect control pressure settings, or interference with the pressure source. In this case, the control pressure source should be inspected to ensure that the pressure has been adjusted to the value specified by the system.

　　(4) Air ingress into the hydraulic system. This is primarily caused by leaks in the system. In such cases, verify the hydraulic reservoir fluid level, inspect the seals and fittings on the pump’s suction side, and check whether the suction line is excessively contaminated. If any of these issues are present, replenish the hydraulic fluid, repair or replace the seals and pipe fittings, and clean or replace the coarse filter.

　　(5) The hydraulic cylinder exhibits slow initial movement. At low temperatures, the hydraulic fluid has high viscosity and poor flowability, resulting in sluggish cylinder operation. To address this, replace the hydraulic fluid with one that offers superior viscosity‑temperature characteristics. In cold conditions, the fluid can be warmed using a heater or by leveraging the machine’s own heat during startup to raise the oil temperature. For normal system operation, the oil temperature should be maintained at approximately 40°C.

　　2. Do not drive a load during operation.

　　The main symptoms include piston rod stalling, insufficient thrust, reduced speed, and unstable operation. The causes are:

　　(1) Internal leakage in the hydraulic cylinder. Internal leakage in a hydraulic cylinder includes excessive wear of the cylinder seals, the rod seal and gland seal, as well as the piston seal, among other sources of leakage.

　　The causes of leakage at the piston rod and seal cover include seal wrinkling, extrusion, tearing, wear, aging, degradation, and deformation; in such cases, the seals must be replaced.

　　The primary causes of excessive wear in piston seals are improper adjustment of the speed-control valve, excessive back pressure, incorrect seal installation, or hydraulic fluid contamination. Additionally, foreign particles may enter during assembly, and substandard seal materials can contribute to the problem. As a result, the actuator may operate slowly or with insufficient force; in severe cases, the piston and cylinder can be damaged, leading to “cylinder‑scoring.” To address these issues, adjust the speed-control valve and perform any necessary procedures and modifications in accordance with the installation instructions.