This design is usually a longer seat in 1 or 2 pieces, It can be supplied with soft inserts like nylons or PEEK, or with special coatings for specific applications.
Usually, these seats are produced with a screw fitting for easy assembly and to provide space for ball movement. Materials can be standard or exotic for best resistance in service.
The hard inserts usually used in this configuration are:
The main feature of the top entry valve is to permit the on-line maintenance seats and ball replacement without take off the valve frome the pipe. These seats find applications at all pressure.