Globe Valve Working Principle

Why name is “Globe valves” are named for their spherical body shape. The two halves of the valve body are separated by an internal baffle which has an opening forming a seat onto which a movable disc can be screwed in to close (or shut) the valve. In globe valves, the disc is connected to a stem which is operated by screw action.

A globe valve is a linear motion valve used to stop, start, and regulate the fluid flow. The globe valve disk can be removed entirely from the flow path, or it can completely close the flow path. During the opening and closing of the valve, the disc moves perpendicularly to the seat.

This movement creates the annular space between the disk and seat ring that gradually closes as the valve closed. This characteristic provides the globe valve good throttling ability required for regulating the flow.

Leakage from the globe valve seat is less as compared to the gate valve, mainly due to right angle contact between the disc and seat ring, which allows tighter seal between seat the disk.

When a globe valve is manually operated, the stem is turned by a hand wheel. Although globe valves in the past had the spherical bodies which gave them their name, many modern globe valves do not have much of a spherical shape, but the term globe valve is still often used for valves that have such an internal mechanism. In plumbing, valves with such a mechanism are also often called stop valves since they don’t have the global appearance, but the term stop valve may refer to valves which are used to stop flow even when they have other mechanisms or designs.

Globe valves can be arranged in such a way that the disk closes against the flow or in the same direction of flow.

When the disk closes in the direction of flow, the kinetic energy of the fluid helps closing but obstructs the opening. This characteristic is preferable when a quick-acting stop is required.

When the disk closes against the direction of flow, the kinetic energy of the fluid obstructs closing but helps to open the valve. This characteristic is preferable when quick-acting start is required.

Types of globe valve

Three types of globe valves used

  1. Z styles:
  2. Y styles:
  3. Angle styles:

Z styles: Globe Valve

The simplest design and most common type is a Z-body. The Z-shaped partition inside the globular body contains the seat. The horizontal seating arrangement of the seat allows the stem and disk to travel at a perpendicular to the pipe axis resulting in a very high-pressure loss.

The valve seat is easily accessible through the bonnet which is attached to a large opening at the top of the valve body. Stem passes through the bonnet like a gate valve.

This design simplifies manufacturing, installation, and repair. This type of valve is used where pressure drop is not a concern and throttling is required.

Y styles:

Y-pattern globe valves, because of the angle of the stem (45 or 60 degrees from the run), give very little flow restriction. typical Y-pattern globe valve. The Y-pattern globe valve is ideally suited for applications requiring almost full flow in a valve, but with the characteristics of a globe valve.Applications for the Y-pattern globe valve include boiler blow-offs and services where mud, grit, and/or viscous fluids may be encountered.

Angle styles:

Angle body valves provide for a 90 degree change of direction which in some installations saves space, material, and installation time.The inner design of the angle body valve offers less flow restriction than the conventional T-pattern, but more than the Y-pattern globe valve.

Best Suited Control:

Linear and Equal percentage.

Applications of globe valve:

  •  Precise flow regulation
  • Frequent and wide throttling operation
  • Suited to very high pressure drops
  • Suitable for most liquids, vapors, gases, corrosive substances
  • General sizes available are 1/2″ to 8″.
  • Pressure limitations are relatively high, ranging from 1480 to 1500 psi, dependent onmaterials of construction, size and temperature.
  • Minimum and maximum temperatures are also very broad ranging from -425°F to 1100°F, depending again on the materials of construction.
  • Depending on the specific construction and application, the globe valve may comply with ASME class II, III, IV, V or VI shut-off requirements.
  • Easily automated and available with positioners, limit switches, and other accessories.

 

Advantages of globe valve

  • Efficient and precise throttling
  • Accurate flow control

 


Disadvantages of globe valve:

  • Low recovery and relatively low coefficient of flow (Cv).
  •  High pressure drop, higher pump capacity and system wear
  • More expensive than other valves
  • The sealing device is a plug that offers limited shut-off capabilities, not always
    meeting bubble tight requirements.

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