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A globe valve is a type of valve primarily used to control flow rate. The selection of a globe valve depends on pressure, size, and specifications. Choosing an unsuitable valve can lead to excessive pressure, unstable regulation, and leakage problems. Therefore, valve selection is crucial.
Understanding the working principle, types, and uses of globe valves is therefore essential. A globe valve is used to open, close, and regulate flow rate. Its main working principle involves moving a disc or plug within the valve body against a fixed seat to control flow rate.
This article will provide a detailed introduction to globe valves, enabling you to select the appropriate one.
What Is a Globe Valve?
The main function of a globe valve is to regulate flow rate. Unlike ball valves and butterfly valves, globe valves involve linear motion. Their internal working principle is that the valve stem moves the valve disc vertically towards or away from the valve seat, changing the flow area within the valve body, thereby controlling the flow rate.
In industrial systems, globe valves are installed in locations where flow rate is slowly regulated. Its application is similar to other valves, only the application location differs. It can be used in cooling water piping systems, boiler systems, oil and gas systems, and air conditioning systems.
The original design of the gate valve had a circular valve body. With the development of technology, the valve body of modern gate valves is no longer limited to a circular shape, but its internal control principle remains unchanged.
What are the Main Parts of a Globe Valve?
A gate valve consists of: valve body, valve core, valve cover, valve disc or valve plug, valve seat ring, valve stem, packing, gasket, and handwheel or actuator.
The composition of these components requires very tight sealing; poor quality or poor sealing will cause leakage.
The functions of each component are as follows:
| Globe Valve Part | Function |
|---|---|
| Body | Main pressure-containing shell |
| Bonnet | Covers the valve body and supports the stem |
| Disc / Plug | Moves up and down to control flow |
| Seat Ring | Sealing surface matched with the disc |
| Stem | Transfers motion from handwheel or actuator |
| Packing | Prevents leakage around the stem |
| Gasket | Seals the body-bonnet connection |
| Handwheel / Actuator | Provides manual, pneumatic, or electric operation |
How Does a Globe Valve Work?
A gate valve operates on a linear motion principle. When the valve stem or handwheel is turned, the valve disc moves up or down, thus affecting the fluid flow rate. This allows for gradual adjustment of the flow rate.
The internal flow of a gate valve is not linear; there is a certain directional deviation, which increases the pressure drop. This effect is crucial in terms of efficiency and load. Engineers can calculate the impact of this using CV values or flow coefficients.
What are the Common Types of Globe Valves?
Globe valves come in different types, the most common being: Z-type, Y-type, angle valve, and needle valve.
Z-type globe valves have a relatively simple structure and are often used in industrial systems. Their limitation is a relatively large pressure drop.
Y-type globe valves have an inclined stem but a relatively smooth flow path. This feature reduces pressure loss, so they are often used in steam or high-temperature systems.
Angle valves can change direction, usually by 90 degrees. This feature can replace the function of an elbow, but offers more functionality.
Needle valves are mostly used in small piping or instrumentation systems for precise flow regulation.
| Type | Main Feature | Typical Use |
|---|---|---|
| Z-Type Globe Valve | Standard body design | General shutoff and throttling |
| Y-Type Globe Valve | Lower flow resistance | Steam, high-temperature pipelines |
| Angle Globe Valve | 90-degree flow direction | Compact piping layouts |
| Needle Globe Valve | Fine adjustment | Instrumentation and small lines |
| 3-Way Globe Valve | Mixing or diverting flow | HVAC and control systems |
The above table lists the characteristics and specific applications of these four types of valves.
What Materials Are Used for Globe Valves?
The materials available for globe valves include: cast iron, ductile iron, carbon steel, stainless steel, bronze, brass, and alloy steel. These different materials correspond to different applications.
Cast iron and ductile iron gate valves are widely used in water treatment systems, including but not limited to drinking water systems and HVAC systems.
Carbon steel gate valves are primarily used in piping systems with high pressure and temperature requirements.
Stainless steel gate valves are frequently used in piping systems transporting corrosive fluids.
Bronze and brass gate valves are commonly used in small-diameter piping systems, such as low-pressure systems for water and gas.
Alloy steel gate valves are often used in high-temperature or high-load applications.
Choosing the appropriate valve material requires comprehensive consideration of its pressure, composition, manufacturing specifications, transported goods, and operating environment.
What Standards Apply to Globe Valves?
Gate valve manufacturing standards include ASME B16.34, ASME B16.5, and ASME B16.30. Other international standards may also apply: BS, EN, DIN, ISO, JIS, or GB standards.
In short, there are many valve manufacturing standards; the specific choice depends on your specific needs.
What are the Advantages and Disadvantages of Globe Valves?
The main advantage of a globe valve is its precise flow control, which is more accurate than that of a gate valve or ball valve.
The disadvantage of a globe valve is its larger pressure drop because the fluid direction changes within the valve body.
| Advantages | Disadvantages |
|---|---|
| Excellent throttling performance | Higher pressure drop |
| Good shutoff capability | Slower operation |
| Suitable for control applications | Heavier than some quarter-turn valves |
| Easier seat maintenance in many designs | Not ideal for dirty or slurry media |
| Available with manual or automated control | Higher actuator force may be required |
Globe Valve vs Gate Valve: What Is the Difference?
The main difference between globe valves and gate valves lies in their functions.
The main function of a globe valve is regulation. It provides better control in pipeline systems requiring flow rate control.
The main function of a gate valve is isolation. It primarily acts as a barrier in pipeline systems.
Globe Valve vs Ball Valve: Which One Should Buyers Choose?
The choice between these two valves depends on your specific needs: regulation or rapid on/off.
Ball valves are quarter-valve valves, allowing for rapid on/off processing. They are often used in small-diameter pipeline systems.
Globe valves are mainly used for regulating flow rate. They allow for gradual adjustment of the fluid flow speed.
For distributors, both types of valves are commonly used. Purchasing can be based on past sales data.
Manual, Pneumatic, or Electric Globe Valve?
Globe valves have three actuation methods: manual, pneumatic, and electric.
Manual: Requires turning a handwheel; if the torque is high, operation can be cumbersome.
Pneumatic: Uses compressed air to move the actuator. Widely used in industrial process control due to its fast response speed.
Electric: Driven by electricity. Primarily used in piping systems requiring remote control.
The choice of actuation method depends on the customer’s specific functional needs.
Where Are Globe Valves Used?
Globe valves are used in various industrial systems, depending on the location. They are used in applications requiring flow rate control, such as air conditioning ducts, steam systems, boiler feedwater systems, and oil and gas systems.
However, in environments with easily deposited substances, care should be taken to prevent clogging or corrosion.
How Should Distributors and Construction Buyers Select a Globe Valve?
Both distributors and construction buyers need to have clear requirements regarding the size, specifications, pressure rating, application temperature, material, transmission medium, and pressure drop of globe valves.
| Selection Item | What to Confirm |
|---|---|
| Size | DN/NPS and pipe schedule |
| Pressure Rating | PN, Class, or working pressure |
| Medium | Water, steam, air, oil, chemical, or gas |
| Temperature | Affects body, trim, and packing selection |
| Flow Requirement | Cv value or flow range |
| Material | Cast iron, carbon steel, stainless steel, bronze |
| Operation | Manual, pneumatic, or electric |
| Standard | ASME, API, EN, DIN, ISO, JIS, or GB |
| Documents | Drawing, datasheet, test report, certificate |
However, distributors may tend to choose standard sizes. Construction buyers, on the other hand, are more likely to purchase sizes that can be actually used in their projects.
What Does a Globe Valve Symbol Mean in Piping Drawings?
The globe valve symbol on piping drawings indicates the location where a globe valve will be used. It will also indicate whether it will be manual, pneumatic, or electric.
These details are crucial for procurement.
Summary
The above provides a detailed introduction to globe valves, covering not only their most obvious regulating characteristics but also other important considerations. Hopefully, this article will be helpful in selecting valves or specific globe valves.
