Which part is not required for an atmospheric type vacuum breaker?

An atmospheric type vacuum breaker is a device designed to prevent backflow and protect water supply systems from contamination. This type of backflow preventer works by ensuring that if there is a drop in system pressure, air can enter the system to prevent a vacuum, thereby stopping any potential siphoning of contaminated water back into the clean water supply.

The components of an atmospheric vacuum breaker include a body (which houses the mechanism), an air inlet flow valve (which opens to allow air into the system when necessary), and a canopy that protects the air inlet from debris and contaminants. While all these components play a vital role in the operation and effectiveness of the device, the shutoff valve is not a required part of this system.

The absence of a shutoff valve from an atmospheric type vacuum breaker is significant because this design is intended to function without the need to isolate the device from the system using a valve. The vacuum breaker operates solely by allowing air to enter the system under conditions of negative pressure, and including a shutoff valve would complicate this straightforward operational principle. As a result, the shutoff valve is not a necessary component, making it the correct answer in this context.