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Air/Vacuum Valve Sample Specification

Air/Vacuum valve(s) shall be installed at high points on the pipeline or as directed by the engineer to exhaust large quantities of air upon system start-up and allow large quantities of air into the pipeline upon system shut-down or line break. As water enters the valve during start-up, the float rises to the seat and seals the outlet. The valve remains closed until system pressure drops to near zero pressure. It should be noted that this valve would not open when the system is pressurized to release accumulating air. When the system pressure drops to near zero pressure, the valve will open and allow air in to prevent the possibility of vacuum formation and a possible pipeline collapse. This also allows the line to be drained rapidly when pipeline maintenance is required.


It should be noted that when this valve is installed in a vault or manhole, there is a possibility of external fluids entering the pipeline and contaminating potable water. For instance, if the manhole floods and the pipeline goes to negative pressure, the Air/Vacuum valve will open and suck the external fluids into the pipeline.


When using an Air/Vacuum valve, there are a number of ways to prevent fluid form entering the system. First, the valve outlet can be piped to a level above the flood line. Secondly, the valve itself can be located at a point above the flood line. Finally, a float device like the one shown below can be used. (See Figure 1) When the external fluid rises, the float rises to seal the outlet thus preventing fluid from entering the system. Keep in mind however, that when the manhole is flooded the Air/Vacuum valve will not allow any air into the system if it goes to negative pressure.


The Air/Vacuum valve should be protected from freezing when located at a station that is subject to freezing. One way to do this would be to fit the valve with a Crispin Thermally Activated Valve (TAV). The Thermally Activated valve is a device that opens up when the temperature approaches freezing and allows the system fluid to be discharged, thus creating movement inside the valve and preventing it from freezing. Also, the valve can be insulated or wrapped with heat tracing to keep the internal temperature above freezing.

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