A vacuum-actuated shear valve coupled between piping from a storage tank and piping internal to a fuel dispenser that automatically opens and closes in response to a vacuum level. A vacuum actuator is provided to control a fuel flow valve inside the shear valve. When a sufficient vacuum level is generated to the vacuum actuator, the actuator keeps the flow path valve inside the shear valve open. When the vacuum is lost, the vacuum actuator releases the flow path valve inside the shear valve, which closes it. The vacuum actuator is coupled to a secondary containment space of a fuel-handling component that is drawn under a vacuum level by a vacuum-generating source to monitor for leaks. Thus, if a leak occurs in the monitored secondarily contained space, the shear valve is automatically closed to prevent the flow of fuel from continuing to be supplied to the source of the leak.