There are 2 types of breakers as per pictures

whatever  type is available at time of order will be supplied

A vacuum breaker is a mechanical device used to avoid back flow or a negative pressure in a plumbing system.

It typically consists of an air valve with a spring holding it closed. When the pressure within the system is positive, the valve remains closed. When the pressure is negative (less than atmospheric), the negative pressure overcomes the force of the spring holding the valve closed and the it opens, typically allowing normal atmospheric air to enter the system, thereby eliminating the negative pressure. Otherwise, the negative pressure might cause back flow of the plumbing system.