Diaphragm and piston are available types of which valve used in water closets?

The correct choice refers to a flushometer, which is a valve specifically designed for use in water closets (toilets). Flushometers utilize either a diaphragm or a piston mechanism to control the flow of water during the flushing process. The diaphragm type uses a flexible membrane that opens and closes to allow water to flow and then seal off once the desired flush is achieved. The piston type operates with moving components that push water through a chamber, similarly controlling the flush cycle.

This design is crucial in providing a consistent, powerful flush while minimizing water usage, making flushometers popular in commercial applications where efficiency is paramount. The operation of diaphragm and piston mechanisms allows for immediate and effective flushing action, which is particularly useful in high-traffic settings.

The other types of valves mentioned serve different purposes. A gate valve is primarily used for on/off control of fluid flow, a check valve prevents backflow in a plumbing system, and a pressure relief valve is designed to release excess pressure in a system. None of these fulfill the specific role that a flushometer does in a water closet setup.