I also see reference to these same parts as American Products 26" Eclipse Valve Upgrade Kit (Before 11-95) 50124100.
If the purpose of the overdrain parts is to diffuse the incoming water into the sand filter, based on pictures it seems that my ordered replacement MPV valve (Praher TM-12-S8) may have a builtin diffuser.
But, overdrain is a confusing term to me.
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