Which type of hydraulic motor requires mechanical devices to prevent internal leakage during start-up?

The correct answer is the vane motor, as this type of hydraulic motor relies on the movement of vanes within a cylindrical chamber to create mechanical work. During the start-up phase, internal leakage is a common challenge due to the design of the motor, where the vanes may not be tightly seated against the chamber walls until sufficient pressure builds up. Mechanical devices, such as check valves or pressure regulators, are often employed to minimize this internal leakage and ensure that the motor begins operating efficiently without significant loss of hydraulic fluid.

In contrast, piston motors typically maintain a more secure sealing capability, which helps control internal leakage even during start-up. Gear motors have a solid design that allows them to operate effectively with minimal concern for internal leakage at low speeds or pressures. Blade motors, similar to vane motors, may experience some leakage but not to the extent that would necessitate specific mechanical devices solely at start-up, making them less reliant on such measures compared to vane motors.