Advantages and Disadvantages of Globe Valve: Globe valve parts and functions are very important for chemical and mechanical engineers because they help in filling out the data sheet.
Welcome to another article where we will discuss an important technical term, especially relevant if you are from the chemical or oil and gas industry. In this article, we will cover globe valve parts and their functions, applications, advantages and disadvantages, recently asked questions (Q&A), and the different types of globe valves.
Table of Contents
What is Globe Valve?
A globe-valve is a linear motion valve primarily used to regulate flow in a pipeline. It has a movable plug or disc element and a stationary ring seat in a generally spherical body. Globe valves are commonly used where throttling and flow regulation are required. Unlike ball valves, globe valves provide better control of flow and can be used for more precise modulation of liquids, gases, and steam.
Working Principle of Globe Valve
The globe valve operates by moving a disc or plug perpendicular to the flow path, pressing against the seat to restrict flow or lifting away to allow flow. When the valve stem is turned, the disc moves up or down to open or close the valve. This linear motion allows for accurate throttling and control of flow rate. The flow typically changes direction inside the valve body, which results in higher pressure drops compared to straight-through valves like ball valves.
Parts of Globe Valve
Body
The body is the outer shell of the globe valve that contains all internal parts. It has an inlet and outlet port and is designed to direct the flow through an S-shaped path to the seat. The body material is selected based on pressure, temperature, and fluid type. Common materials include stainless steel, carbon steel, and cast iron.
Disc or Plug
The disc (or plug) is the movable part that regulates flow by moving toward or away from the seat. It presses firmly against the seat to provide a tight seal when closed and lifts away to allow flow when open. Discs come in various shapes such as flat, spherical, or tapered, depending on the valve design and intended application.
Stem
The stem connects the disc to the handwheel or actuator. When the handwheel is turned, the stem moves the disc up or down in a linear motion. The stem is sealed with packing to prevent leaks, usually using gland packing or O-rings.
Bonnet
The bonnet covers and encloses the valve stem and packing. It is bolted or screwed to the body, providing access for maintenance and assembly. The bonnet also supports the stem and provides a seal against leakage.
Handwheel or Actuator
The handwheel is used for manual operation of the valve, allowing precise control by turning it to move the disc. In automated systems, an actuator (electric, pneumatic, or hydraulic) replaces the handwheel for remote or automatic control.
Packing and Seals
Packing surrounds the stem to prevent leakage where the stem exits the valve body. Materials like graphite, PTFE, or elastomers are used depending on the operating conditions. Additional seals and gaskets ensure leak-tight assembly between the body and bonnet.
This assembly makes globe valves suitable for applications requiring good throttling control and frequent operation.
Globe Valve Types
Key types of globe valves are.
Z-Type Globe Valve
The Z-type globe-valve has a body that forms a Z-shaped flow path. The fluid enters and exits at right angles, changing direction twice before flowing through the valve. This design offers better throttling control but results in a higher pressure drop. It is widely used in general service applications requiring moderate flow control.
Y-Type Globe Valve
The Y-type globe valve body is angled so the flow changes direction only once, reducing turbulence and pressure drop compared to the Z-type. The angled design makes it suitable for applications where lower pressure loss and moderate throttling are required, such as in steam and gas systems.
Angle Globe Valve
The angle globe-valve combines the inlet and outlet ports at a 90-degree angle, allowing the valve to change flow direction without using additional elbows in the piping. It is useful for systems requiring flow direction changes and precise throttling control, common in HVAC and fluid transport systems.
Needle Globe Valve
The needle globe-valve uses a slender, tapered needle-shaped disc that fits into a matching seat. It provides very fine control of flow, making it ideal for low flow rates or precise adjustments in instrumentation or laboratory applications. Its design allows for smooth, gradual throttling.
Stop Check Globe Valve
The stop check globe-valve combines the functions of a check valve and a globe valve. It allows flow in one direction and stops flow back in the opposite direction while still providing throttling control. It is commonly used in boiler feed water systems and steam applications.
Advantages and Disadvantages of Globe Valve
Disadvantages of Globe Valve
- Higher pressure drop due to flow path changes
- Generally larger and heavier than other valve types
- More complex design, leading to higher cost
- Not suitable for quick on/off operation
- Requires more force or larger actuator for operation
- Potential for seat and disc wear in abrasive fluids
- Can be noisy at high flow rates due to turbulence
Advantages of Globe Valve
- Excellent flow regulation and throttling capability
- Provides tight shut-off and good sealing
- Suitable for frequent operation and easy to operate
- Allows easy inspection and maintenance of internal parts
- Versatile for various fluids like steam, water, oil, and gases
- Precise control over flow rate
- Durable and reliable in high-pressure applications
Recently Asked Questions With Their Answers
What is a globe valve used for?
Answer
A globe valve is used for flow regulation and throttling in pipelines, allowing precise control over flow rate in liquid, gas, or steam systems.
What is the working principle of a globe valve?
Answer
It works by moving a disc perpendicularly against a seat to restrict or allow flow. The linear motion allows accurate flow control by changing the valve opening size.
Why do you need a globe valve?
Answer
Globe-valve are needed when precise flow control, modulation, or throttling is required, such as in cooling water systems, fuel oil systems, or steam control.
What is the difference between globe valve and gate valve?
Answer
Globe-valve provide better flow control with throttling ability, while gate valves are mainly for on/off control with minimal pressure drop.
What materials are globe valve made from?
Answer
Common materials include stainless steel, carbon steel, cast iron, bronze, and sometimes special alloys depending on the fluid and operating conditions.
How do you choose between different types of globe valves?
Answer
The choice depends on factors like pressure drop tolerance, flow control needs, installation space, and fluid type. For lower pressure drop, Y-type or angle globe valves are preferred.
Conclusion
Globe-valves are essential in applications where flow control and throttling are critical. Their design provides precise regulation but causes higher pressure drops compared to other valves. Understanding the parts, types, advantages, and limitations of globe-valves helps engineers select the right valve for their specific needs, ensuring safe and efficient system operation.
References
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