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Questions and Answers
What is a primary function of a ball valve?
What happens when you rotate a ball valve by 90 degrees?
Which of the following about ball valves is NOT true?
In what scenario is using a ball valve potentially hazardous?
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Which material is frequently used to construct the ball in a ball valve to handle corrosive fluids?
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Which category do ball valves belong to?
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What is a disadvantage of using a ball valve?
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What type of pipe applications are butterfly valves mainly used for?
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What is a key advantage of diaphragm valves?
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Which type of diaphragm valve is best suited for high flow, slurry applications?
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What is a disadvantage of using diaphragm valves?
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Which statement accurately describes non-return valves?
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What is the primary function of a shuttle valve?
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In terms of valve types, what is a key feature of check valves?
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Which valve type is less effective as a control valve compared to globe-type control valves?
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What is the primary reason diaphragm valves are considered effective in preventing contamination?
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What is the main operation method of a butterfly valve?
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What is a significant disadvantage of butterfly valves?
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Which type of valve is well-suited for applications requiring cleanliness and chemical compatibility?
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How do reciprocating stem valves provide a tight seal?
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What happens when a butterfly valve is fully closed?
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Which statement is true regarding double seated sliding stem globe valves?
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What is a common hazard associated with butterfly valves?
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How do you achieve flow control with reciprocating stem valves?
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Study Notes
Control Valves
- Two main types of control valves are: Rotating Stem and Reciprocating Stem
Rotating Stem Valves
- Ball Valves:
- Used for on/off duties and not for accurately controlling flow rates
- Basic construction: spherical ball in a pipeline with a hole through the center allowing fluid flow
- Closed by rotating the ball 90 degrees, presenting the sides of the sphere to the fluid
- Opened by rotating the ball 90 degrees back, presenting the hole in the sphere to the flow
- Simple to operate and suitable for controlling corrosive materials
- Ball can be constructed from corrosion-resistant material (PTFE)
- Can operate at high temperatures and pressures (e.g., 200°C and 300 atmospheres)
Ball Valve Advantages
- Low pressure loss when open
- Easy to operate
- No lubrication required, minimizing contamination risk
- Excellent seal, resulting in minimal leakage
- Can be used for corrosive materials
- Can be used with suspensions but frequent cleaning may be required
Ball Valve Disadvantages
- Not suitable for accurate flow control
- Product can be trapped behind the ball, resulting in bacterial growth and contamination
Butterfly Valves
- Commonly used in large diameter pipelines for controlling gas and steam flows
- Circular disc in a pipeline that rotates 90 degrees
- Fully open position: disc is parallel to the flow, allowing full flow
- Fully closed position: disc is perpendicular to the flow, stopping the flow
- Often fitted with sealing rings to ensure complete shut-off
Butterfly Valve Advantages
- Cheap and reliable
- Fast and easy to operate (only 90 degree rotation)
- Takes up minimal space
- Offers low resistance to flow when fully open
Butterfly Valve Disadvantages
- Prone to leaks if not properly locked into position
- Fast flowing or dense liquids can push the valve open
- Product can become trapped, resulting in bacterial growth
Reciprocating Stem Valves
- Use a closing gate that travels perpendicularly to the receiving seat, sealing the valve shut
- Common types: single and double seated sliding stem globe valves
- Construction of single and double seated globe valves:
- Actuator: provides the plug that seals or opens the valve
- Valve body: houses the plug
- Actuator can be operated manually or automatically
Reciprocating Stem Valve Advantages
- Effective for flow control
- Opening size can be adjusted easily, providing control over the orifice size
- Single seated valves provide a tight seal
Reciprocating Valve Disadvantages
- Double seated valves can be prone to leaks and should be used with another valve or a single seated valve for tight seals
- Seals may require frequent replacement if corrosive or high pressure liquids are transferred
- Product can get trapped in the seats of these valves
Diaphragm Valves
- Used when cleanliness, bubble-tight shutoff, and chemical compatibility are critical
- Streamlined flow path, absence of cavities, and minimal contact surfaces, make it less likely to cause contamination
- Two main types are: Weir style and straightway diaphragm valve
- Straightway valve is suitable for high flow, slurry applications due to its unobstructed flow path
Diaphragm Valve Advantages
- Streamlined path, absence of cavities, and minimal contact surfaces make it less likely to cause contamination
- Wide range of diaphragm materials available, suit various applications and fluid types
- Can be used effectively as control valves, but not as effective as a globe type control valve
- Easy to maintain
- Reliable closure, the resilient diaphragm seats tightly against the weir
- Prevention of leakage, the diaphragm protects components that may be prone to corrosion
Diaphragm Valve Disadvantages
- Not suitable for high temperature or pressure applications
Shuttle Valves
- Used to alter the direction of flow between two ports
Non-Return Valves (Check Valves)
- Allow flow in one direction only
- Two main types: hinged and ball non-return valves
- Can be spring loaded to require a specific pressure to open the valve
- Close automatically when the flow stops or reverses, preventing fluids from flowing back to the vessel of origin
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Description
This quiz covers the major types of control valves with a focus on the ball valve. Learn about the construction, operation, and advantages of using ball valves in various applications. Ideal for those studying engineering or fluid dynamics.
