In June 2005 and starting with serial # 12039, Brownie's made a technology update to our Valve Plate Assembly. For a clear indication that your system has the OLD style valve plate, you will need to open it up and view it. IF the valve restraint on your valve plate is black and plastic, you have the older style and need to update it in order for the current style flapper valves to fit. The current Valve Restraint is Aluminum.
Pictured is the current Flapper Valve. It requires 2 per valve plate @ $10 EACH.
ADDITIONAL UPDATE: Your valve plate may have 2 flappers per side of your valve plate (total of 4 flappers per valve plate) The current Flapper Valve is a bit thicker and stronger. Therefore - you will only require 1 Flapper Valve per side of each valve plate (total of 2 flappers per valve plate)