Control Valve Types (Gate Valve, Globe Valve, Ball Valve etc.)!

Summary

This video script offers an insightful overview of various valve types, including globe, gate, ball, plug, butterfly, diaphragm, check, pinch, and safety valves. It explains how valves are named, their functions in controlling flow and pressure, and the differences between rotary and linear motion valves. The script also covers the advantages and disadvantages of each valve type, their ideal applications, and the role of actuators in their operation.

Takeaways

• 🔧 Valves are named after the type of discs they use, which control the flow of substances through them.
• 🌐 Globe valves are an exception, named for the shape of the valve body rather than the disc.
• 🔄 Valves serve various functions like stopping, starting, varying, controlling direction, regulating pressure, and relieving overpressure.
• 🔧 Rotary valves, such as ball, plug, and butterfly valves, require a 1/4 turn to change from open to closed positions and are fast-acting.
• 📉 Linear motion valves like gate and globe valves operate by raising or lowering the disc and are slower than rotary valves.
• 🛠️ Actuators for valves can be mechanical, electrical, hydraulic, or pneumatic, determining how the valve is operated.
• 🏐 Ball valves are not suitable for throttling due to their design, but they have a very low pressure drop when fully open.
• 🦋 Butterfly valves are advantageous for large applications due to savings in weight, space, and cost, and have a low pressure drop when open.
• 🔨 Diaphragm valves are ideal for handling corrosive or contaminated fluids due to minimal parts exposure to the medium.
• 🚰 Gate valves are simple, cheap, and have low pressure drop when open, but are not suitable for throttling and can be prone to wear and leakage.
• 🌡️ Globe valves have less seat leakage and are easier to open, but they have a higher pressure drop and can be noisy and heavy.
• 🤏 Pinch valves are simple, inexpensive, and have almost no pressure drop, making them suitable for slurries with suspended solids.
• 🔩 Plug valves are similar to ball valves but with a different disc shape, offering low pressure drop and adaptability for multiport applications.
• 🔄 Check valves prevent flow reversal in a system, using mechanisms like weight, back pressure, or springs to operate.
• 💉 Needle valves allow for fine adjustments in fluid flow, often used as metering valves due to their precise control.
• 🛡️ Relief and safety valves protect equipment from overpressure by gradually or rapidly opening to release excess pressure.

Q & A

What is the primary function of a valve?

Valves are used for stopping and starting flow, varying the amount of flow, controlling the direction of flow, regulating downstream system or process pressure, and relieving system over and under pressure.

How do valves get their names?

Valves are almost always named based on the type of discs used, such as ball, butterfly, and gate valves, which are named after their respective shapes. However, globe valves are named after the shape of the valve body itself.

What are the two main categories of valve motion?

Valves can be categorized as rotary or linear motion valves. Rotary valves require a 1/4 turn to change position, while linear motion valves raise or lower the disc to control flow.

Why are ball valves not suitable for throttling or regulating flow?

Ball valves are not suitable for throttling or regulating flow because they are designed for fast-acting, on-off control. The pressure drop across ball valves when fully open is very low, which is not ideal for throttling.

What are the advantages of butterfly valves over other valve types for larger applications?

Butterfly valves offer advantages such as savings in weight, space, and cost, especially for larger applications. They also have a low pressure drop when fully open and are well-suited for handling large flows of liquids or gases at relatively low pressures.

How does a diaphragm valve operate and what makes it suitable for handling corrosive fluids?

A diaphragm valve operates by raising or lowering a flexible diaphragm onto the valve seat to control flow. It is suitable for corrosive fluids because very few parts are exposed to the flowing medium, with only the diaphragm and internal flow passages in contact, preventing contamination.

Why are gate valves prone to excessive vibration when only partially open?

Gate valves are prone to excessive vibration when partially open because the flow stream can cause the valve disc to vibrate, especially if the flow is turbulent or at high velocities.

What are the main designs of globe valves?

The main designs of globe valves are straight flow, angle flow, cross-flow, and Y-flow, each offering different flow patterns and control characteristics.

How do pinch valves operate and what makes them suitable for handling slurries with large amounts of suspended solids?

Pinch valves operate by compressing a sleeve made of rubber or synthetic material using a pinching mechanism. They are suitable for slurries with large amounts of suspended solids due to their large seating area and because the operating mechanisms are isolated from the flowing medium, preventing wear and contamination.

What is the purpose of a check valve in a piping system?

A check valve is designed to prevent the reversal of flow in a piping system. It allows flow in one direction and closes when there is a reversal of flow, maintaining the correct flow direction and protecting the system.

How do relief and safety valves differ in their operation?

A relief valve gradually opens as the inlet pressure increases above the setpoint to relieve overpressure, while a safety valve rapidly pops fully open once the pressure setting is reached and stays open until the pressure drops below a reset pressure, providing a quick response to overpressure conditions.