When is a hydraulic pump classified as a constant-displacement type?

A hydraulic pump is classified as a constant-displacement type when it produces a continuous positive pressure. This means that the pump is designed to deliver a consistent volume of hydraulic fluid with each stroke, regardless of the load pressure. In a constant-displacement pump, the displacement remains the same, which results in a steady flow rate as long as the pump is operating. The continuous positive pressure ensures that the hydraulic system receives a reliable and uninterrupted supply of fluid, which is essential for maintaining performance and efficiency in hydraulic applications.

The other options do not accurately define the characteristic of a constant-displacement pump. A variable output pressure indicates a different classification of pump that can adjust its pressure based on system requirements. Continuous circulation of fluid can occur in both constant-displacement and variable-displacement systems, making it not specific enough to define the type. Finally, a pump that can completely stop fluid flow does not describe a constant-displacement pump, as that implies an ability to alter the flow or pressure, which is contrary to the characteristics of a constant-displacement design.