This double check valve is a backflow prevention device designed to protect water supplies from contamination. It's often a local authority requirement in plumbing installations.

It has two internal, spring loaded, non-return valve mechanisms. This employs two operating principles: firstly one check valve will still act, even if the other is jammed wide open. Secondly the closure of one valve reduces the pressure differential across the other, allowing a more reliable seal and avoiding even minor leakage.

22mm compression pipe connections on each end.