Which statement about hydraulic motors is true?

Hydraulic motors are designed to convert hydraulic energy into mechanical energy, and one of the key characteristics of hydraulic motors is that many of them are indeed positive displacement devices. Positive displacement motors operate by trapping a specific amount of fluid and then converting that volume of fluid into mechanical movement. This design allows for a more consistent and controllable output torque and speed compared to other types of hydraulic devices.

While there are hydraulic motors that operate at high efficiency, it’s not accurate to say that all of them do. The efficiency can vary based on design and operating conditions. Additionally, although many hydraulic motors can reverse flow direction, not all designs allow for this flexibility, making it a somewhat misleading generalization. The statement about their use primarily in low-speed applications also does not universally apply, as hydraulic motors can be found in a range of applications, including those requiring variable speeds.

Thus, the affirmation that hydraulic motors are all positive displacement types highlights a fundamental aspect of their operation, underlining that positive displacement is a common and significant characteristic in hydraulic motor design.