NEIEP Mechanics Practice Exam

When a hydraulic elevator is held at a floor, what device prevents the piston from descending?

1. Safety Valve

2. Check Valve

3. Pressure Regulator

4. Release Valve

The correct answer is: Check Valve

In a hydraulic elevator, the device that prevents the piston from descending while held at a floor is the check valve. This component allows fluid to flow in one direction only, which is critical in maintaining the position of the elevator when it is stationary. When the elevator is held at a specific floor, hydraulic pressure lifts the piston, and the check valve ensures that this pressure is maintained by preventing the fluid in the cylinder from flowing back into the reservoir. As a result, this mechanism secures the elevator at the desired height, blocking any unintended descent that might occur due to the effects of gravity or fluctuations in the hydraulic pressure system. In contrast, other devices mentioned serve different functions. For instance, a safety valve is designed to relieve excess pressure in the system to prevent damage, a pressure regulator manages and stabilizes pressure levels throughout the system but does not hold the elevator in position, and a release valve allows fluid to escape from the cylinder, permitting the piston to lower, which is not desired when the elevator is at rest at a floor.