BRINGING RELIABILITY TO HIGH PRESSURE HYDRAULIC CYLINDERS

摘要

High system pressure, defined as 6,000 psi (41,000 kPa or 410 bar), is the pressure setting on some newer excavator functions. A system that operates at 6,000 psi will see short pressure spikes that are two to three times the working pressure. This means the components need to handle 12,000 to 18,000 psi (82,737 to 124,105 kPa or 827 to 1,241 bar) pressure spikes for a reasonable service life of 8,000 hours, or four years, and should not fail in less than 2,000 hours, or one year of service. CYLINDER DESIGN CONSIDERATIONS When a machine or attachment is being designed, the designer has an idea of what the unit should do and how it should be done. As soon as you hand the machine to a different operator, the application, duty cycle, and operating parameters have changed. In some cases the change is enough that things start to fail. Frequently, the cylinder will be subjected to a work-induced load that is much greater than what is possible by direct control. Both counterbalance valves and pilot-operated check valves are used to hold a cylinder in position, and both valves can produce additional loads on the cylinder components when in operation. Some load-holding valve settings are increased by back pressure on the pilot port.