AstralPool / Hurlcon Check valve. Used in E, CX, TX, CTX pumps. Suits both 40mm & 50mm unions. These prevent impeller "spin-off" from water rushing backwards through the pump, mainly when it switches off.
New style check valve (fully white) replaces the older black and white style.**
**Important Note: In some cases, the flap won't fully open in 40mm tails. Unfortunately there is no way to tell until you try. If it does not open fully, you will need to fit a above the pump.