A hopper is equipment which temporarily stores materials such as coal, ore, gravel, grit, screenings, or dewatering cake and discharges the necessary amount onto the conveyor. In general, a hopper has a square box construction with a narrower, funnel-shaped bottom; a gate attached to the bottom opens and closes to drop the required amount of the material. The gate opens when the rod of the Power Cylinder attached to it retracts, and closes when the rod extends. This equipment is often installed outdoors. The cylinder requires a press stopping mechanism to prevent the contents from falling while the gate is closed.