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Questions and Answers
What is the primary function of non-return valves?
What is the primary function of non-return valves?
Which type of valve is specifically designed to maintain downstream pressure?
Which type of valve is specifically designed to maintain downstream pressure?
What characterizes special service valves?
What characterizes special service valves?
What is the temperature rating range for general service valves?
What is the temperature rating range for general service valves?
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Which of the following valves is used to prevent backflow during pump shutdown?
Which of the following valves is used to prevent backflow during pump shutdown?
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In what ways can throttling valves operate?
In what ways can throttling valves operate?
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What distinguishes severe service valves from other types?
What distinguishes severe service valves from other types?
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Which is NOT a characteristic of general service valves?
Which is NOT a characteristic of general service valves?
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What is the cavitation index threshold for a globe valve with reduced trim size, flow over the plug, to be considered incipient cavitation?
What is the cavitation index threshold for a globe valve with reduced trim size, flow over the plug, to be considered incipient cavitation?
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What material hardness is recommended for valve construction to prevent cavitation damage?
What material hardness is recommended for valve construction to prevent cavitation damage?
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Which of the following modifications can help prevent cavitation in a valve system?
Which of the following modifications can help prevent cavitation in a valve system?
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For a ball valve that is 900 open with a full trim, what is the incipient cavitation index?
For a ball valve that is 900 open with a full trim, what is the incipient cavitation index?
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What action should be taken if the cavitation index falls between incipient and choked levels?
What action should be taken if the cavitation index falls between incipient and choked levels?
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If a valve's cavitation index is 0.38, what does this indicate about the valve's flow situation?
If a valve's cavitation index is 0.38, what does this indicate about the valve's flow situation?
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What is the choked cavitation index for a globe valve over the plug with full area?
What is the choked cavitation index for a globe valve over the plug with full area?
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What flow direction is associated with a globe valve that has a choked cavitation index of 0.52?
What flow direction is associated with a globe valve that has a choked cavitation index of 0.52?
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What causes cavitation in a liquid flowing through a valve?
What causes cavitation in a liquid flowing through a valve?
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Which of the following best describes the process of cavitation?
Which of the following best describes the process of cavitation?
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What is the primary cause of water hammer in process applications?
What is the primary cause of water hammer in process applications?
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What effect does cavitation primarily have on a valve over time?
What effect does cavitation primarily have on a valve over time?
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What is a cavitation index used for?
What is a cavitation index used for?
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Which of the following can cause water hammer due to rapid valve closure?
Which of the following can cause water hammer due to rapid valve closure?
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What is the maximum acceptable stroking duration for closing a valve?
What is the maximum acceptable stroking duration for closing a valve?
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How does increasing pressure affect the vapor bubbles in a cavitation scenario?
How does increasing pressure affect the vapor bubbles in a cavitation scenario?
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What role does the flow velocity play in the cavitation process within a valve?
What role does the flow velocity play in the cavitation process within a valve?
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What can be a consequence of water hammer in piping systems?
What can be a consequence of water hammer in piping systems?
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What can be a direct consequence of cavitation occurring near a valve's surface?
What can be a direct consequence of cavitation occurring near a valve's surface?
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Which frequency range is most sensitive to human hearing?
Which frequency range is most sensitive to human hearing?
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Which method is effective in minimizing water hammer in valves?
Which method is effective in minimizing water hammer in valves?
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What is the permissible noise level (dBA) for a duration of 4 hours?
What is the permissible noise level (dBA) for a duration of 4 hours?
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Which of the following statements about cavitation is incorrect?
Which of the following statements about cavitation is incorrect?
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What effect does turbulence in valves typically have?
What effect does turbulence in valves typically have?
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What is one effect of low-frequency noise on humans?
What is one effect of low-frequency noise on humans?
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What can be done to handle unexpected surge in a fluid system?
What can be done to handle unexpected surge in a fluid system?
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Which of these factors is NOT a common consequence of water hammer?
Which of these factors is NOT a common consequence of water hammer?
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What is a benefit of upgrading the packing box in valve maintenance?
What is a benefit of upgrading the packing box in valve maintenance?
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Which sealing method does not require continual retightening?
Which sealing method does not require continual retightening?
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What is a primary motivation for addressing fugitive emissions in valve maintenance?
What is a primary motivation for addressing fugitive emissions in valve maintenance?
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What can cumulative and irreversible hearing damage begin with?
What can cumulative and irreversible hearing damage begin with?
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Which of the following equipment may be affected by valve performance issues due to noise and vibration?
Which of the following equipment may be affected by valve performance issues due to noise and vibration?
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What is a common cause of leakage in a valve that has recently been repaired?
What is a common cause of leakage in a valve that has recently been repaired?
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Which of the following is NOT a potential cause of excessive wear on a valve seat?
Which of the following is NOT a potential cause of excessive wear on a valve seat?
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What must be ensured before disassembling and reassembling a valve?
What must be ensured before disassembling and reassembling a valve?
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What action should be taken if a leak persists after tightening the bolts?
What action should be taken if a leak persists after tightening the bolts?
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During troubleshooting of a valve, what is the recommended practice?
During troubleshooting of a valve, what is the recommended practice?
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If a valve is used in a corrosive application, what should be done before maintenance?
If a valve is used in a corrosive application, what should be done before maintenance?
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Which condition can rarely cause damage to a valve's body or bonnet?
Which condition can rarely cause damage to a valve's body or bonnet?
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What should be done if there is evidence of foreign material between the gate and seat?
What should be done if there is evidence of foreign material between the gate and seat?
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Study Notes
Valve Maintenance
- Valves are mechanical devices designed to direct, start, stop, mix, or regulate the flow, pressure, or temperature of a process fluid.
- Different classes of valves exist based on their function, application, and design, including styles, sizes, and pressure ranges.
- Common valve types include plug, ball, globe, butterfly, and gate valves.
- Materials used in valve construction vary, including steel, iron, plastic, brass, and specialized alloys.
Basic Valve Components
- The internal components of a valve are collectively called trim.
- Typical trim includes the disc, seat, stem, and sleeves to guide the stem.
- Valve performance is determined by the interaction between the disk and seat, and the disk's position relative to the seat.
Types of Valves
- Manual Valves: These valves are typically operated manually (e.g., by a handwheel or lever). Some manual valves can be motorized through actuators.
- Control Valves: These are automatically operated valves designed to control flow, temperature, or pressure. They are often used for precise regulation.
Types of Valves (continued)
- Ball Valves: Ball valves are characterized by a spherical closure element that rotates to open and close the flow.
- Gate Valves: These valves use a gate-like closure element that opens and closes to regulate the fluid flow like a gate.
- Plug Valves: Plug valves feature a plug-type closure element that rotates to control the flow.
- Globe Valves: Used in a wide variety of applications that require regulation. They have a body with a globe-shaped structure and often accommodate various different types of trim.
Classification of Valves
-
By Function:
- On-off valves: used to block or allow flow.
- Non-return valves: allow flow in only one direction.
- Throttling valves: regulate flow at different points between fully open and fully closed.
-
By Application:
- General service valves: widely applicable.
- Special service valves: designed for specific applications (e.g., high pressures, corrosive fluids).
- Severe service valves: designed for unusual or demanding applications.
-
By Motion:
- Linear valves: move in a straight line to control flow (e.g., gate, globe, pinch).
- Rotary valves: rotate to control flow (e.g., ball, plug, butterfly).
Common Valve Problems
- High pressure drops
- Cavitation: the formation and implosion of vapor bubbles in a fluid.
- Flashing: the conversion of liquid to vapor when the vapor pressure is reached.
- Choked flow: a restriction on the flow rate of a gas or vapor due to the velocity reaching sonic speeds.
- High velocity
- Water hammer: pressure surge caused by rapid changes in flow direction.
- High noise level
- Fugitive emissions/leakage
Valve Maintenance
- Visual inspections, especially for leakages.
- Correct tightening of bolts when leakages are observed and maintaining procedures
- Regularly checking for wear and/or damage to gaskets, and packing.
- Inspecting for leaks in all possible locations. Replacing parts when needed/possible.
- Inspecting for wear and/or damage to seats, bodies, and/or plugs.
- Maintaining and troubleshooting as needed to ensure efficient operation and prevent potential damage.
- Regular inspections and maintenance are critical for valve upkeep and reliability.
Valve Nomenclature
- Different standards (e.g., ANSI, ISO) define valves and pipelines.
- Measurements such as pipe diameter (DN) and pressure ratings (PN) are standardized to ensure compatibility and efficiency in systems.
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Description
Test your knowledge on different types of valves and their specific functions with this comprehensive quiz. Explore concepts like non-return valves, throttling valves, and cavitation thresholds to deepen your understanding. Ideal for students and professionals in engineering and fluid dynamics.
