Which type of valve allows an elevator car to be lowered in the event of a power failure?

The correct choice identifies the manual lowering valve, which plays a crucial role in ensuring safety during a power failure in elevator systems. When a power outage occurs, this valve allows for the controlled descent of the elevator car, enabling it to lower safely to the nearest landing. By engaging the manual lowering valve, an operator can take direct action to manage the descent, ensuring passenger safety and minimizing the risk of uncontrolled falls.

In contrast, other types of valves do not serve the same function. A relief valve is designed primarily to release excess pressure within the hydraulic system, which is essential for protecting the system from damage but does not facilitate lowering the car during a power failure. An automatic lowering valve is intended to engage automatically under specific conditions but may not provide the same level of operator control as a manual option. Spring-loaded valves function differently, using tension to maintain pressure or flow within the system rather than being directly involved in the process of enabling a controlled descent. Thus, the manual lowering valve is the most appropriate mechanism for the safe and controlled lowering of an elevator in case of a power interruption.