Instrumentation Piping Valves

Globe Valves

Globe valves have proved to be very popular recently since the globe valve design allows very fine regulation characteristics. They are very popular to be used as control valves.

The name 'globe valve' originates from the spherical shape of the valve body. The globe valve body is divided into two halves by a partition or a baffle. These two halves can be connected by an opening at the center of the partitioning which divides the valve body in two halves. A small horizontal disc or plug is the closure member which can move up and down attached to the stem, thus opening or closing the valve.

This design offers good regulation characteristics but causes more pressure drop across the valve due to high disturbance in the flow path. This pressure drop can be reduced to some extent by increasing the opening area in the partition to bring it up closer to cross sectional area of the pipe. Also, the partition can be angled in order to make the flow across the partition smoother and thus to reduce the pressure drop.

The discs or the plugs in globe valves, which are the closure members can be available in wide variety.

The discs in contact with the seat closes the valve. The seat can be damaged by formation of solid deposits. Hence globe valves are suitable only for clean service. Also discs are not as effective as using plugs for throttling. For vapor service, discs cannot provide positive isolation, unless they are made of a resilient material.

The plugs for globe valves are also available in a wide variety from needle shape to semi-disc shape. The contour of the plug can be designed to specifically achieve the desired throttling characteristic. For example, needle shaped plugs are finest for flow control.

The seats for discs or plugs can either be integrated with the body or can be screwed or welded to it. Depending on the application and service, wide range of materials can be used for the seat rings.

Advantages of globe valves

Globe valves are best known for the throttling capacity. They also have good shut-off capacity. Compared to gate valves they have shorter stroke.

Disadvantages of globe valves

The torturous path of the flow through a globe valve causes a larger pressure drop compared to other valves. Also, to close the valve, the disc needs to be seated with opposition from flow under the seat. Hence great force or a large actuator is needed to operate the valves.

Applications of globe valves

  • Flow control for cooling water systems, fuel oil systems and other service where flow regulation is important.
  • Vents and drains requiring leaktight valves.
  • Control valves applications.

 

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