Description of application of seals in hydraulic equipment

Application of seals in hydraulic equipment
In the machining industry, hydraulic transmission applications are very wide, such as semi-automatic hydraulic drive lathes and so on. During the use of these machine tools, there are often faults such as impact and creep. During the diagnosis and maintenance, the cause of the failure is often found on the hydraulic control components (such as pumps and valves), which causes the maintenance work to be in trouble.
Eventually such failures are often found on the actuators, namely the severe wear of the cylinder piston seals. This type of phenomenon is particularly evident in O-ring seals.
Case: A semi-automatic lathe of a program-controlled hexagonal turret. During the use, there is a failure phenomenon that the feed speed of the turret cannot be adjusted. After the shut-off valve 2 is closed, there is still crawling and rushing, and it can be stopped until the bottom of the cylinder. The machine tool cannot be used normally.
Oil testing and repair: Check all hydraulic control components, especially the governor components, for no problems. Some speed control valves have been replaced and the fault has not been eliminated. After the dismantling of the cylinder, it was found that the O-ring of the piston was seriously worn, which caused the hydraulic oil in the two chambers of the cylinder to smash. Analyze the reason, because the O-ring seal wears, the cylinder has a gap between the rod cavity and the rodless cavity. When the speed control valve 3 or the shut-off valve 2 is closed, it is equivalent to cutting off the oil return path of the rod cavity. Theoretically speaking, when the pressure oil enters the rodless cavity of the cylinder, a thrust F is formed on the piston, which causes the piston to move toward the rod cavity. Because the cylinder has the rod cavity returning to the oil, the oil in the cavity is rapidly formed. Back pressure, so that the two ends of the piston are balanced and still, at this time F = F no, and the no-cavity oil pressure is different due to the different force area of the piston, that is, P has "P no." In practice, due to the gap between the two chambers of the cylinder, the pressure oil in the cylinder chamber has a tendency to flow from the high pressure zone to the low pressure zone. When the flow occurs, the pressure P in the cavity decreases, P does not rise, and the thrust acts on both ends of the piston. F no "F", the piston loses balance and seeks a new balance point to move with the rod cavity. In this way, the piston moves until it has an external force to stop. The occurrence of the above phenomenon has a great impact on the maintenance work of the machine tool. After replacing the O-ring seal of the cylinder piston, the machine fault is eliminated and the operation returns to normal.