What prevents the piston in a duplex pump from striking the head?

The reason a cushion formed by the piston covering the exhaust port prevents the piston in a duplex pump from striking the head is integral to the pump's design and operation. In a duplex pump, as the piston moves towards the head at the end of its stroke, it covers the exhaust port. This coverage creates a pressure buildup in the chamber, leading to a hydraulic cushion effect.

This cushion acts as a buffer that absorbs the impact energy and slows down the piston before it can make contact with the head. By preventing a hard impact, the design enhances the longevity of the pump and ensures a smoother operation, reducing wear and potential damage to both the piston and the pump casing.

In contrast, spring tension, fluid backpressure, and valve tension may play roles in the operation of the pump, but they do not specifically address the immediate concern of preventing piston-to-head contact during operation.