What type of buffers must be used for speeds below 50 fpm?

The correct answer is that solid buffers must be used for speeds below 50 feet per minute (fpm). Solid buffers are specifically designed to absorb kinetic energy effectively in low-speed applications, making them suitable for elevators operating at slower speeds. They consist of a solid structure that can compress to absorb the force of an impact, providing a reliable and stable stopping mechanism for elevators.

In the context of elevators, utilizing solid buffers ensures safety and stability at lower operational speeds. They minimize potential damage and provide a firm stop without the complexities involved with other types of buffers that may be better suited for higher speeds.

Other options involve buffer types designed for different scenarios. Spring buffers, for instance, can be effective for absorbing energy but are generally more appropriate for moderate speeds. Hydraulic buffers are often used in applications needing stronger force absorption capabilities typically found in faster-moving elevators. Magnetic buffers may be used in advanced systems but are not standard for lower speed applications and could introduce unnecessary complexity. Each of these alternatives might have specific advantages but is ultimately not aligned with the requirement for elevators operating below 50 fpm.