Globe Valve

Globe Valve

Body Designs of Globe Valves

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

  • Tee Pattern or Z-body

  • Angle Pattern

  • Wye Pattern or Y-body body

Tee Pattern  or Z-shaped Globe Valve Design

Tee Pattern Globe valve design is the most common body type, with a Z-shaped diaphragm. The horizontal setting of the seat allows the stem and disk to travel perpendicular to the horizontal line. This design has the lowest coefficient of flow and higher pressure drop. They are used in severe throttling services, such as in bypass lines around a control valve. Tee-pattern Globe valves may also be used in applications where pressure drop is not a concern and throttling is required.

Angle Body Globe Valve

Angle Pattern Globe valves design is a modification of the basic Tee 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 wye-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.

Wye Pattern Globe valves

Wye Pattern Globe valves design, is an alternative for the high pressure drop, inherent in Globe valves. Seat and stem are angled at approximately 45 degrees, what gives a straighter flowpath 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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Introduction of Globe Valves

As their name suggests, globe valves are linear motion valves with rounded globular shaped bodies. Since their shape is similar to other valve bodies, positive identification must be made based on internal piping. Recently globe valves have lost their traditional round body-shape. Globe valves have many advantages and disadvantages for users. They have excellent and precise throttling ability for high-pressure systems. The disadvantages include low-flow coefficients and a longer operating time because the operator must turn the handle and stem many times to ensure the valve is completely open or completely closed. Globe valves can be used in systems that require frequent stroking, vacuum, and systems that have a wide range of temperature extremes

A Globe valves is a linear motion valve and are primarily designed to stop, start and regulate flow. The disk of a Globe valve can be totally removed from the flowpath or it can completely close the flowpath.

Conventional Globe valves may be used for isolation and throttling services. Although these valves exhibit slightly higher pressure drops than straight=through valves (e.g., gate, plug, ball, etc.), they may be used where the pressure drop through the valve is not a controlling factor.

Because the entire system pressure exerted on the disc is transferred to the valve stem, the practical size limit for these valves is NPS 12 (DN 300). Globe valves larger than NPS 12 (DN 300) are an exception rather than the rule. Larger valves would require that enormous forces be exerted on the stem to open or close the valve under pressure. Globe valves in sizes up to NPS 48 (DN 1200) have been manufactured and used.

Globe valves are extensively employed to control flow. The range of flow control, pressure drop, and duty must be considered in the design of the valve to avert premature failure and to assure satisfactory service. Valves subjected to high-differential pressure-throttling service require specially designed valve trim.

Generally the maximum differential pressure across the valve disc should not exceed 20 percent of the maximum upstream pressure or 200 psi (1380 kPa), whichever is less. Valves with special trim may be designed for applications exceeding these differential pressure limits.

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Typical Applications of Globe valves

The following are some of the typical applications of Globe valves:

  • Cooling water systems where flow needs to be regulated

  • Fuel oil system where flow is regulated and leaktightness is of importance

  • High-point vents and low-point drains when leaktightness and safety are major considerations

  • Feedwater, chemical feed, condenser air extraction, and extraction drain systems

  • Boiler vents and drains, main steam vents and drains, and heater drains

  • Turbine seals and drains

  • Turbine lube oil system and others

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A globe valve, different from ball valve, is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body.

Globe valves are named for their spherical body shape with the two halves of the body being separated by an internal baffle. This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve. The plug is also called a disc ordisk. In globe valves, the plug is connected to a stem which is operated by screw action using a handwheel in manual valves. Typically, automated globe valves use smooth stems rather than threaded and are opened and closed by an actuator assembly.

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