Filter drain cap split!

I have a Hayward sand filter with a 2hp 2spd pump. The drain cap split when changing from high to low spd. I notice the pump lid and fiter valve assembly move quite abit when changing speeds. I have a 2" pipe for backwash with a 3ft piece of heavy clear reinforced hose connecting the filter to the pipe. When I backwash and change from high speed to low speed the hose will flatten out for a second. I guess due to the volume and flow change of the water. I bought an extra cap in case it happens again. Maybe something others will want to monitor.