Valterra Swing/Spring Check Valve [1-1/2" Slip] [1/2 lb.] (200-C15) bathpumps and FC-9830 reference give this

and FC-9830 reference give this part practical value because DE grid replacements work best when the new component matches the original filter geometry and internal connection style closely

6" fitting size

Helps restore original seat-level water behavior

The FC-3746

Valterra Swing/Spring Check Valve [1-1/2" Slip] [1/2 lb.] (200-C15) bathpumps and FC-9830 reference give thisThe Valterra 1 1 2 inch slip swing and spring check valve is designed for compatible plumbing systems that need one way flow control with a 1 2 pound cracking pressure style response. A check valve is useful because it helps limit unwanted backflow and supports more stable system behavior when circulation stops or flow direction changes. This replacement is especially useful when the original valve no longer seals consistently, has become unreliable