What are air/vacuum valves?

Air/vacuum valves are float operated and designed to exhaust large volumes of air from a pipeline during pump startup as the pipeline is being filled. The valve also admits large volumes of air when the pipeline is draining to prevent a vacuum from forming, which can potentially lead to a pipeline collapse. When the pipeline fills, fluid raises the float to shutoff the valve. When the pipeline drains, the float drops to allow air to enter.