What is the difference between a gate valve of the solid wedge type and a flexible wedge type?
The solid wedge is one piece and machined to fit the seat of the housing for a good seal, whereas in a flexible wedge design, the wedge has an annular groove that allows the wedge to bend within the seat of the housing.
Gate valves with a solid wedge are considered the most economical. Almost all small gate valves, NPS 2 (DN 50) and smaller, are solid wedge gate valves. Solid wedge gate valves are generally used in medium to low pressure and temperature applications. It is common to use solid wedge gate valves made of cast iron or ductile iron in cold or ambient water pipelines.
The flexible wedge is also a one-piece construction like a solid wedge, but in a flexible wedge design the wedge is provided with an annular groove which allows the wedge to flex within the body seat. This construction compensates for changes in seat alignment for a better seat while maintaining the strength of a solid wedge in the center. This design offers improved puncture resistance and performance in situations with the potential for thermal bonding.