The Cla-Val Pacific 35WW Series Air and Vacuum Valve is designed to perform two separate functions in a sewage or wastewater system. First, it will allow large quantities of air to be exhausted from the pipeline as it is being filled. When this air has been vented completely, liquid will enter the valve causing the float to seal tightly against the seat. Secondly, if the line is being drained, the valve responds to the loss in pressure and opens. This allows air to re-enter the pipeline and prevents potentially damaging vacuum from developing.