Pressure applied at any point on a given volume of fluid is transmitted equally in all directions. This means that when multiple hydraulic cylinders are used, each cylinder will extend or retract at its own speed, with the speed determined by the pressure required to move the load. If the cylinders have the same rated capacity, the one subjected to the lighter load will move first, while the one bearing the heavier load will follow later. To ensure synchronized motion of the cylinders—so that the load can be lifted at the same speed at every point—the system must incorporate control valves or components of a synchronized lifting system.

The merits and drawbacks of a hydraulic cylinder must be evaluated in relation to a specific benchmark; otherwise, no meaningful comparison can be made. Broadly speaking, the advantages of hydraulic cylinders can be described from several perspectives:

1. The hydraulic cylinder is as compact and refined as a flashlight, yet, compared with a pneumatic cylinder, it can withstand a working pressure of 15 tons—100 megapascals.

2. The hydraulic cylinder is manufactured from high-quality No. 45 carbon steel, offering excellent fatigue resistance, impact resistance, and non-magnetic properties, while its self-weight has been reduced by two-thirds.

3. The hydraulic cylinder operates over a temperature range of –60 to 200°C, boasts an exceptionally long service life, and can run for 6,000 hours without experiencing any failures.

4. Hydraulic cylinders are the pinnacle of hydraulic components and hydraulic technology; accordingly, their innovative designs and diverse operating modes constitute one of their key features.

Disadvantages of hydraulic cylinders:

1. The design formulas for hydraulic cylinders are inadequate, making it impossible to achieve a high safety factor. Consequently, the structural and strength‑design theories for hydraulic cylinders remain underdeveloped, resulting in certain limitations in their dynamic performance.

2. The load conditions on hydraulic cylinders are often underestimated, leading to unavoidable safety risks, such as piston rod fracture inside the cylinder.

3. Compared with pneumatic cylinders, hydraulic cylinders are more prone to oil leakage, resulting in significant consumption of the working fluid—hydraulic oil.

Hydraulic transmission principle: It uses oil as the working fluid, transmits motion through changes in the sealed volume, and transmits power via the pressure within the oil.

1. The power section converts the mechanical energy of the prime mover into hydraulic pressure energy. For example, a hydraulic pump.

2. The actuating component converts the hydraulic energy supplied by the pump into mechanical energy to drive the working mechanism, such as hydraulic cylinders and hydraulic motors.

3. The control section is used to regulate and adjust the oil’s pressure, flow rate, and flow direction. Examples include pressure control valves, flow control valves, and directional control valves.

4. The auxiliary components integrate the first three sections into a cohesive system, providing functions such as oil storage, filtration, metering, and sealing. Examples include pipelines and fittings, oil tanks, filters, accumulators, seals, and control instruments.