this is the response we received back from Kochek;
All of our dry hydrant strainers are designed to be able to flow at least 1000 GPM in a properly designed system (per NFPA recommendations) under ideal conditions. We recommend that this strainer be installed with at least 6-8” of water above the top plate.
The actual achievable flow rate is more dependent on the design of the complete system than on the strainer itself. Considerations such as lift height, total length of the system, etc. will all affect the flow capacity.
Answered on 6/18/2013 by Butch