Which of the following is NOT one of the three types of isolation valves?

The correct choice is based on the classification of valve types commonly used in piping systems. Isolation valves are specifically designed to stop the flow of fluid in a system when maintenance or repairs are needed. The three primary types of isolation valves are ball, gate, and globe valves.

Ball valves offer quick shut-off capabilities and are ideal for on/off control, making them very efficient and durable. Gate valves provide a straight-line flow path and are advantageous when a minimum pressure drop is required; they are designed primarily for fully open or fully closed positions. Globe valves, while often used for regulation of flow, can also serve as isolation valves due to their ability to provide a tight seal.

In contrast, check valves are not used for isolation purposes. Instead, their primary function is to allow flow in only one direction and to prevent backflow. This operational role distinguishes check valves from the isolation valves, which are intended to control or shut off the flow entirely. Therefore, identifying check valves as not fitting within the category of isolation valves is correct.