The 1/4" orifice is used in the Brower VP2 valves to accommodate water pressures lower than 60 PSI. The orifice can be replaced in any of the VP2 valves by removing the base from the top and switching out the original orifice.
Made of poly, the Brower Plunger and valve seat will open and close around the orifice once the water in the trough has reached it's set level.