Mainly three main types of discs are used in globe valves.
The ball disk
The composition disk
The plug disk
The ball disc is used is applications involving low pressure and low temperature systems. The ball disk is so arranged that it fits on a tapered, flat-surfaced seat. Though the ball disc can be used for throttling purpose, the efficiency might not be as expected.
The replaceable composition discs are designed with a hard, non-metallic insert ring on the disc which helps in creating additional tightness. Such rings are used in steam and hot water applications as they help in preventing erosion and damaging the globe valve from solid particles.
The plug disk is mainly used for applications which require excessive throttling. The disk provides better throttling than ball and composite disks because of its long and tapered design.