Hydraulic cylinder With a simple structure and reliable operation, it is a hydraulic actuator that converts hydraulic energy into mechanical energy to produce linear reciprocating motion. When used for reciprocating motion, it can eliminate the need for a reduction gear, features zero transmission backlash, and delivers smooth movement, making it widely employed in various mechanical hydraulic systems. A hydraulic cylinder essentially consists of a piston and piston rod, a cylinder barrel and end caps, sealing elements, a cushioning device, and an exhaust device. While the cushioning and exhaust devices depend on the specific application, the other components are indispensable.

　　Hydraulic cylinders come in a wide variety of structural configurations, and they can be classified in numerous ways: based on the type of hydraulic pressure, they are divided into single‑acting and double‑acting types; according to their mode of motion, they are categorized as linear reciprocating or rotary oscillating; by structural design, they include plunger, piston, multi‑stage telescopic sleeve, and gear‑rack types; by mounting configuration, they are available with tie‑rod, eye‑type, foot, or hinge mounts; and by pressure rating, they are classified as 16 MPa, 25 MPa, 31.5 MPa, and so on.

　　Hydraulic cylinder principle: The operating principle of all cylinders is essentially the same; a jack is, in fact, a simple hydraulic cylinder. Hydraulic fluid is pumped into the cylinder via a manual pressure‑boosting lever (a manual hydraulic pump) and a check valve. At this point, the fluid entering the cylinder cannot flow back due to the check valve, forcing the piston rod to move upward. During operation, more hydraulic fluid continues to enter the cylinder, driving it steadily upward. When lowering, the hydraulic valve opens, allowing the fluid to return to the reservoir. This is the basic operating principle; all other designs are improvements built upon it.

　　Selection of hydraulic cylinders: When choosing a hydraulic cylinder, we typically base our decision on the cylinder’s bore diameter, stroke length, working pressure, and mounting configuration. In addition to these factors, there are several other considerations worth noting. First, when the cylinder’s operating speed after load application reaches a certain threshold, a cylinder equipped with a cushioning device should be used; alternatively, at higher speeds, an external flow‑control valve should be installed. Second, exercise caution in selecting both the hydraulic fluid and the seals. Different hydraulic fluids require seals made from compatible materials to ensure the cylinder’s service life.

　　Because hydraulic cylinders must withstand substantial pressure—higher loads correspond to higher pressures—maintenance of the cylinder is a critical component of overall hydraulic system upkeep. The hydraulic cylinder serves as the heart of the hydraulic system; once this “heart” malfunctions, repairs can be difficult, so meticulous care is essential. 1. Prevent rust. Since the piston rod extends outside the cylinder during operation, it is exposed to oxidation and corrosive gases. To protect it, apply an appropriate amount of grease to guard against corrosion that could weaken the piston and even cause it to fracture under load. 2. Replace the oil upon opening the unit. Over time, foreign particles may enter the cylinder, increasing friction during use. Additionally, hydraulic fluid has a limited service life; if left unchanged for too long, internal components can become damaged or corroded. 3. Maintain an appropriate operating speed—keep it below 2 m/s—to prolong the cylinder’s lifespan. Furthermore, to safeguard the mechanism and ensure safety, installing internal cushioning devices is highly effective in protecting the cylinder.