I just purchased a Hayward SP0712 Series Vari-Flow Valve and cannot get it to screw into my Truflo TM 60 fiberglass sand filter. It is the same model valve as was previously on the filter, which WILL screw on. The new valve will not catch the threads properly to screw on. The filter is very old, and the valve I'm replacing is 17 years old. I'm pretty sure the threads on the valve are not aligning properly to the threads on the sand filter. Does anyone have any suggestions other than buying a new sand filter? Thanks.