Wegman valves offers various types of check valves
2 plates or doors open to one side when the flow push against them, they are being held in the closed position by a light spring when there is no flow and hardly any pressure drop is required to open them.
When the flow is being turned for some reason the doors are closed by the flow which stops the backlfow of medium into the upstream pipe.
The are typically metal seated but also available with a soft seat.
Available in wafer, lugged and double flange body style.
Common are Carbon Steel, Stainless Steel but also higher grade materials can be supplied