Well, obviously you can't remove the check ball and spring which is located in the injector body however, I don't run the additional check ball and spring which is typically found in the filter/strainer.
I run a larger(plastic with 316ss screen) AG filter/strainer at the end of the suction tube which doesn't have a check ball and spring. I purchased the one designed for 3/8" hose. I run 3/8" suction line to 8" before the injector and step it back down to the 1/4" for the injector barb.
I've got 12' of the 3/8" line running to my chem tank. With the stainless SSS injector, it'll suck the balls off of a goat!!!