Which type of hydraulic cylinder uses hydraulic fluid on both sides for motion?

A double-acting cylinder is designed to utilize hydraulic fluid on both sides of the piston to produce motion. This configuration allows for fluid to enter one side of the cylinder to push the piston in one direction, while simultaneously allowing fluid to return from the other side, which enables the piston to retract. This bidirectional function provides greater efficiency and control over the cylinder's movement compared to other types of cylinders.

In contrast, a single-acting cylinder relies on hydraulic fluid on only one side of the piston. It typically uses a spring or gravity to return the piston to its original position once the pressure is released. This limits its capabilities to a single direction of movement. A pneumatic cylinder uses compressed air instead of hydraulic fluid and generally operates similarly to a single-acting or double-acting cylinder, but it is not classified as a hydraulic device. A hydraulic ram, while a type of hydraulic device, operates by using the principles of fluid dynamics to create a pressure surge, rather than functioning like a traditional cylinder that moves both ways with hydraulic fluid on either side.

Thus, the double-acting cylinder stands out for its use of hydraulic fluid to facilitate movement in both directions, making it the most versatile and widely used type in hydraulic applications.