I've created an auto siphon that does not stop siphoning water at a grow bed flow rate of higher than 62 GPH. Is it possible that the pipe under the grow bed is too long? The pipe has since been cut to the point marked in the picture in red - but it didn't seem to help. The siphon has a 4" gravel guard with a 2" bell. The inner tube goes from 1" to 3/4" with 2 90 degree turns in the piping.
Pictures included - Thanks!
Put an elbow at the bottom of the standpipe that goes from 3/4 up to 1 1/2 inch and use 1 1/2 pipe for your long run under the grow bed. Air actually needs to enter from the bottom to stop the siphon.
Jonathan, thank you for your advice. I just got back from installing the 1 1/2" PVC pipe and corner piece - Works perfectly now! :D