Dry hydrant horizontal pvc strainer with fixed cover comes in 6 or 8 inch. The fixed cover does not flap open if there is any debris in the system bigger then the strainer holes thus you would not able to back flush with a fixed cover.
The horizontal pvc strainer with back flush cover comes in 6, 8, or 10 inch. The horizontal back flush is the preferred strainer which allows the pvc line to be back flushed. Debris can be removed because the flap comes up on the end of the strainer.
The horizontal pvc strainer with fixed cover and check valve comes in 6 or 8 inch. The check valve is used when there is a long horizontal run and the pipe is not filled with water due to drought level. Instead of trying to pull a suction with air in the pipe it is backfilled with water, the check valve holds most of the water in, then a draft can be pulled.