Replace main drain valve

[grizwall]

I need to remove air cap from main drain to replace valve. When I remove air cap will water flow out main drain pipe?

 

[ajw22]

Show us pictures of what you need to remove.

 

[grizwall]

I need to cut off 90 elbow to add a 90 sweep elbow to connect the new valve. The elbow I need to cut off is the main drain. Will water from the pool come out after I cut off the elbow. Pool water level is below the return.