What is Globe Valve and How does It Work?

 

Globe valves are linear motion closing-down valves in which the closure member is moved squarely on and off the seat. Usually the closure member is referred as a disc, irrespective of its shape. The seat opening varies in direct proportion to the travel of the disc. This proportional relationship between valve opening and disc travel is ideally suited for duties involving regulation of flow rate. Globe valves are most suitable for throttling and controlling fluid flow and are generally employed in small size piping.

 

Globe valve design necessitates two changes in the direction of flow and this causes resistance in liquid lines and objectionable pressure drop. The installation of globe valves is made so that the flow is up through the seat ring and against the bottom of the disc. This prevents accumulation of dirt and debris above the disc.

 

 

Globe valves may be used for most duties encountered in fluid handling process piping systems. Although the globe valve can be used as a block or isolation valve, it is primarily designed to regulate flow in the partially open position, while gate valves are designed for either the fully opened or fully closed position. When considering globe valves for on-off isolation service, design selection should receive careful consideration because maintaining a tight seal against the strong force pushing up on the disc is difficult. The globe valve, compared to the gate valve, has a short stem travel between the open and closed positions, has relatively little wear and is easier to repair.

 

Globe Valve Working Principle

A globe valve is primarily designed to stop, start and regulate flow. It is comprised of a movable disk and a stationary ring seat in a generally spherical body. The seat of a globe valve is in the middle of and parallel to the pipe, and the opening in the seat is closed off with the disk. When the handle is turned, manually or through an actuator, a disc is lowered or raised by means of the valve stem. When the disc is fully lowered, the fluid flow is shut off. When the disc is fully raised, the fluid flow is at its maximum rate. When the disc is in raised to less then maximum level, the fluid flow is regulated with proportion to the vertical travel of the disc.

 

Globe Valve Body Patterns

There are three primary body patterns or designs for Globe valves, namely:

• Standard Pattern (also known as Tee Pattern or T – Pattern or Z – Pattern)

• Angle Pattern

• Oblique Pattern (also known as Wye Pattern or Y – Pattern)

 

 

Standard Pattern or T – Pattern

Standard pattern globe valve body design is the most common body type. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the flow direction of the fluid. Due to its tortuous flow passage this design offers highest resistance to flow among all of the available patterns. This design has the lowest coefficient of flow and highest pressure drop. They are used in severe throttling services, such as in bypass lines around a control valve. Standard pattern globe valves may also be used in applications where pressure drop is not a major concern and only throttling is required.

 

Angle Pattern

Angle pattern globe valve body design is a modification of the basic standard pattern globe valve. The ends of this Globe valve are at an angle of 90 degrees, and fluid flow occurs with a single 90 degrees turn. They have a slightly lower coefficient of flow than oblique pattern globe valves. They are used in applications that have periods of pulsating flow because of their capability to handle the slugging effect of this type of flow.

 

If the globe valve is to be mounted near a pipe bend, the angle pattern valve body offers two advantages. First, the angle pattern design has a greatly reduced flow resistance compared to the standard pattern design. Second, the angle pattern design reduces the number of pipe joints and saves a pipe elbow.

 

Oblique Pattern or Y – Pattern

Oblique Pattern globe valve body design is an alternative for the high pressure drop, inherent in globe valves. Oblique pattern design reduces the flow resistance of the globe valve to a minimum. Seat and stem are angled at approximately 45 degrees, what gives a straighter flow-path at full opening and offer the least resistance to flow. They can be cracked open for long periods without severe erosion. They are extensively used for throttling during seasonal or startup operations. They can be rod through to remove debris when used in drain lines that are normally closed.

 

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