What type of pump has a built-in pressure control valve?

The type of pump that features a built-in pressure control valve is the rotary-vane pump. Rotary-vane pumps are designed to provide a consistent flow of fluid while also automatically adjusting the output pressure. This is achieved through their integrated pressure control mechanisms, which help maintain the desired pressure level within the system without the need for additional external components.

In contrast, centrifugal pumps operate based on rotational energy but do not typically include a built-in pressure control valve; they require external systems to manage pressure fluctuations. External gear pumps, similar to centrifugal pumps, are used in applications where fluid transfer is essential, but they do not incorporate pressure regulation features directly within the pump design. Deep-well turbine pumps are specialized and are primarily used for extracting water from deep underground sources but lack a built-in pressure control valve for managing output pressure.

Understanding the specific functionalities of these pumps, particularly how the rotary-vane pump’s design incorporates pressure control mechanisms, highlights why it stands out as the correct answer.