Globe Valve Disks:
Many globe valves use one of three basic disk designs: the composition disk the ball disk, and the plug disk.
Ball Disk
The ball disk fits on a tapered, flat-surfaced seat. A ball disk design is used primarily in associatively low pressure and low temperature systems. That is capable of throttling flow, but is generally used to start and stop flow.
Composition Disk
The composition disk design uses a hard, nonmetallic insert ring in the disk. The insert ring creates a tighter closure. Composition disks are generally used in steam and hot water applications. They resist erosion and are enough resilient to close on solid particles without damaging the valve. The Composition disks are replaceable.
Plug Disk
Since of its configuration, the plug disk gives better throttling than ball or composition designs. These are available in a variety of specific configurations. In common, they are all tapered and long.
Globe Valve Disk and Stem Connections
Globe valves employ two techniques for connecting stem and disk: T-slot construction and disk nut construction. Within the T-slot design, a disk slips over the stem. Within the disk nut design, a disk is screwed within the stem.
Globe Valve Seats
Globe valve seats are either integral along with or screwed inside the valve body. Several globe valves have backseats. A backseat is a seating arrangement which gives a seal among the stem and bonnet. While the valve is fully open, the disk seats against the backseat. A backseat design avoids system pressure from building against the valve packing.
Globe Valve Direction of Flow
For low temperature globe, applications and angle valves are ordinarily installed so that pressure is under the disk. This promotes simple operation, helps protect the packing and eliminates a certain amount of erosive action to the seat and disk faces. To high temperature steam service the globe valves are installed so in which pressure is above the disk. Or else, the stem will contract upon cooling and tend to lift the disk off the seat.