Queries on combination air valves 2

[win]

Hi, i have a question about air valves.

Would somebody explain to me the difference between the large orifice air valve and the small orifice air valve.
I understand that the large orifice is meant to allow high volumes of air and water to enter the pipe. However, why is a smaller orifice air valve still needed and paired with a large orifice in a combination valve? Correct me if i am wrong but since the large and small orifice uses floats, when air builds up within the pipeline the large orifice also would be able to expel the air right?

 

[bimr]

A combination valve combines the functions of ai release and vacuum relief. It allows the use of on valve and one connection to the piping instead of tw connections. Conventional valves contain linkage mechanisms for float assemblies. The large venting orifice exhausts large quantities of air from a pipeline being filled and admit large quantities of air into a pipeline being drained.

The small orifice is used to release air slowly during operation while the larger orifice is used for startup and shutdown when the air volumes are much greater.

 

[SteveWag]

The title suggests a “combination” air valve. These typically have a large float and a large vent, with the float rising (or falling) with water level. BUT, the large float may seal the large orifice and say there if air accumulates and the pressure is constant or higher. It is held shut by differential pressure and the area of the orifice. It will not vent any gas. So, a small orifice and a seat are added with the small float moving the seat via a linkage. The un-buoyed weight of the small float is heavy enough to un-seat the small orifice on falling water. In the event of loss of pressure and water, the large float/orifice opens and lets air enter so as to prevent a vacuum.
Steve

 

[win]

Thanks for the explanation! I understand the concept now.