Pneumatic quick connect female fittings contain which component to prevent air from leaking when disconnected?

Pneumatic quick connect female fittings are designed with a check valve component specifically to prevent air from leaking when the connection is disconnected. The check valve allows air to flow in one direction while preventing backflow when the fitting is disengaged. This is critical in pneumatic systems to maintain pressure and prevent air loss during disconnection.

The other components mentioned, such as pressure regulators, ball valves, and gate valves, serve different functions within a pneumatic system. A pressure regulator adjusts the pressure of the air supplied to downstream components, a ball valve controls the flow of air through a passage but does not inherently prevent backflow, and a gate valve is commonly used for on/off control rather than flow regulation. Thus, the design of pneumatic quick connect female fittings relies on the check valve to ensure an airtight seal when disconnected, making it the correct answer.