Which of the following are examples of backflow prevention devices?

Backflow prevention devices are essential components in plumbing systems designed to prevent the reverse flow of contaminated water into the clean water supply. Each of the listed devices serves this vital purpose.

An air gap is a physical separation between the end of a water supply outlet and the highest possible water level in a receptacle, ensuring that any backflow cannot reach the supply line by providing a space where water cannot bridge. This is one of the simplest and most effective forms of backflow prevention.

An atmospheric type vacuum breaker operates by allowing air to enter the system to break a vacuum if the water flow stops. This prevents negative pressure from drawing contaminated water back into the potable water supply.

A pressure vacuum breaker is another effective device that utilizes a mechanical mechanism to allow air into the system when the pressure drops, thus preventing backflow due to siphoning. It is suitable for continuous pressure applications and adds an additional layer of protection against backflow.

Since all of these devices serve the purpose of backflow prevention through varied mechanisms, choosing all of the above is justified. Together, they represent different methodologies to safeguard the potable water supply from contamination due to backflow.