Supplement: Five components of hydraulic cylinder: cylinder barrel, cylinder head, piston and piston rod, sealing device, buffer device and exhaust device. The working principle of each cylinder is similar. Hydraulic oil enters the cylinder through a single valve through a manual booster rod (hydraulic manual pump). At this time, the hydraulic oil entering the cylinder cannot retreat due to the single valve, forcing the piston rod upward. Then the hydraulic oil continues to enter the hydraulic cylinder during work, thus rising continuously. When it is about to descend, the hydraulic valve opens to make the hydraulic oil tank. This is the simplest working principle, and everything else is improved on this basis.