Globe valve belongs to the forced sealing valve. So when the valve is closed, pressure must be applied to the disc so that the sealing surface does not leak. When the medium enters valve 6 from the bottom of the disc, the resistance to be overcome by the operating force is the friction between the valve rod and the packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve rod is larger, otherwise, the valve rod will be bent. In recent years, since the appearance of the self-sealing valve, the flow direction of the medium of the globe valve is changed from the top of the valve disc to the valve chamber. Under medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve rod can be correspondingly reduced. When the globe valve is opened, the opening height of the disc is 25% – 30% of the nominal diameter. When the flow has reached the maximum, it means that the valve has reached the fully open position. Therefore, the fully open position of the globe valve shall be determined by the stroke of the disc.
What is a Globe Valve?
Globe valve, also known as the stop valve, belongs to the forced sealing valve. So when the valve is closed, pressure must be applied to the disc so that the sealing surface does not leak. When the medium enters the valve from the bottom of the disc, the resistance to be overcome by the operating force is the friction between the valve rod and the packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve rod is larger, otherwise, the valve rod will be bent. The connection mode, it can be divided into three types: flange connection, screw connection, and welding connection. After the appearance of the self-sealing valve, the flow direction of the medium of the globe valve is changed from the top of the valve disc to the valve chamber. Under medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve rod can be correspondingly reduced. At the same time, under the action of the medium, this type of valve is also strict. “Standardization, serialization and universalization” of the value in China stipulates that the flow direction of the globe valve shall be from top to bottom. When the globe valve is opened, the opening height of the disc is 25% – 30% of the nominal diameter. When the flow has reached the maximum, it means that the valve has reached the fully open position. Therefore, the fully open position of the globe valve shall be determined by the stroke of the disc.
How does a Globe Valve work?
The opening and closing parts of the globe valve are plug-shaped discs, the sealing surface is flat or conical, and the disc moves in a straight line along the centerline of the fluid. The movement form of the valve rod includes the lifting rod type (the valve rod is lifted and the handwheel is not lifted) and the lifting rotating rod type (the handwheel is rotated and lifted together with the valve rod, and the nut is set on the valve body). The globe valve is only suitable for full open and full close, and it is not allowed to regulate and throttle.
The advantages of Globe valve are as follows:
- It is simple in structure and it is easy to manufacture and maintain.
- Small working stroke, short opening and closing time.
- Good sealing performance, small friction between sealing surfaces, and long service life.
The disadvantages of Globe valve are as follows:
- The fluid resistance is large, and the force required for opening and closing is large.
- It is not suitable for medium with particles, high viscosity, or coking medium
- Poor regulation performance.
Types of globe valve:
According to the position of the stem thread, the type of globe valve is divided into external thread type and internal thread type. According to the flow direction of the medium, there are straight-through types, direct current types, and angle types. According to the sealing form, the globe valve is divided into packing seal globe valve and bellows seal globe valve.
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Tee Globe Valve
This is the most common body type for a globe valve. 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 highest pressure drop. They’re used in severe throttling services, such as in bypass lines around a control valve. When pressure drop is not a concern and throttling is required, this globe valve design is a good solution.
Angle Globe Valve
The third type among globe valve types is the angle globe valve which represents a shift in the configuration of the Z-shaped basic glove valve. The entry and exit ends are located at the right angles. The diaphragm may be a plain flat plate with its ends at right angles. The fluid can flow down more symmetrically than discharge from the ordinary globe with just one turn in 90. The angle body style has a particular benefit as it can be used as both a valve and a pipe elbow. The angle valve closely resembles the ordinary globe for moderate pressure, temperature, and flow conditions.
The angle globe valve can be used to control the slugging effect in fluctuating flow conditions. In terms of fluid mechanics and erosion, the release conditions of the angle valve are favorable. In high-pressure applications, these features are extremely important. The valve operates more or less like the Z Shaped Valve under mild conditions.
Y Type Globe Valve
The Y-type design is a solution for the high-pressure drop problem in Z-type valves. In this type, the seat and stem are angled at approximately 45° to the pipe axis. Y-body valves are used in high pressure and other critical services where pressure drop is concerned.
Structure of Globe valve body:
The structure of globe valve body includes a straight-through type, straight flow type, and right angle type. Straight through type is the most common structure, but its fluid resistance is the largest. The straight flow type has less resistance and is mostly used for fluid with solid particles or high viscosity. The right-angle valve body is mostly forged, which is suitable for the globe valve with a small diameter and high pressure.
For the installation and maintenance of Globe valve, the following items shall be noted:
- The globe valve of the hand wheel and handle operated can be installed at any position of the pipeline.
- Hand wheel, handle and transmission mechanism are not allowed to be used for lifting.
- The flow direction of the medium shall be consistent with the arrow direction shown in the valve body.
The globe valve has the following advantages:
- In the process of opening and closing, the friction of the sealing surface is smaller than that of the gate valve, which is wear-resistant.
- The opening height is small.
- Generally, there is only one sealing surface, with a good manufacturing process and easy maintenance.
There are many kinds of globe valves, which can be divided according to the position of the thread on the stem:
1. Upper thread stem globe valve
The thread of the globe valve stem is on the outside of the valve body. Its advantage is that the valve stem is not eroded by the medium, and it is easy to lubricate. This structure is widely used.
2. Lower thread stem globe valve
The thread of the globe valve stem is in the valve body. The stem thread of this structure is in direct contact with the medium. It can be easily eroded and cannot be lubricated. This kind of structure is used in small caliber and low-temperature areas.
According to the channel direction of the globe valve, it can be divided into: straight through globe valve, angle globe valve and three-way globe valve. The latter two kinds of globe valves are usually used to change the flow direction of the medium and distribute the medium.
