Valves and Their Functions Quiz
48 Questions
5 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of non-return valves?

  • To only allow fluid to flow in one direction (correct)
  • To increase the pressure of the fluid
  • To allow fluid to flow in multiple directions
  • To regulate the temperature of the fluid

Which type of valve is specifically designed to maintain downstream pressure?

  • Isolation valve
  • Throttling valve
  • Pressure regulator (correct)
  • Check valve

What characterizes special service valves?

  • Designed for general applications without modification
  • Designed specifically for particular applications (correct)
  • Suitable for high-pressure environments only
  • Capable of managing severe pressure fluctuations

What is the temperature rating range for general service valves?

<p>-50°F to 650°F (D)</p> Signup and view all the answers

Which of the following valves is used to prevent backflow during pump shutdown?

<p>Non-return valve (B)</p> Signup and view all the answers

In what ways can throttling valves operate?

<p>Both manually and automatically (C)</p> Signup and view all the answers

What distinguishes severe service valves from other types?

<p>They prevent adverse effects in challenging applications. (B)</p> Signup and view all the answers

Which is NOT a characteristic of general service valves?

<p>Designed for extremely high pressures (C)</p> Signup and view all the answers

What is the cavitation index threshold for a globe valve with reduced trim size, flow over the plug, to be considered incipient cavitation?

<p>0.93 (B)</p> Signup and view all the answers

What material hardness is recommended for valve construction to prevent cavitation damage?

<p>Rockwell hardness 40 or higher (B)</p> Signup and view all the answers

Which of the following modifications can help prevent cavitation in a valve system?

<p>Implementing air injection (C)</p> Signup and view all the answers

For a ball valve that is 900 open with a full trim, what is the incipient cavitation index?

<p>5.2 (D)</p> Signup and view all the answers

What action should be taken if the cavitation index falls between incipient and choked levels?

<p>Use special trim or hard materials (C)</p> Signup and view all the answers

If a valve's cavitation index is 0.38, what does this indicate about the valve's flow situation?

<p>The valve is choked and cannot increase flow further (B)</p> Signup and view all the answers

What is the choked cavitation index for a globe valve over the plug with full area?

<p>0.56 (C)</p> Signup and view all the answers

What flow direction is associated with a globe valve that has a choked cavitation index of 0.52?

<p>Under the plug with full or reduced trim (D)</p> Signup and view all the answers

What causes cavitation in a liquid flowing through a valve?

<p>Liquid pressure dropping below vapor pressure (A)</p> Signup and view all the answers

Which of the following best describes the process of cavitation?

<p>Vapor bubbles collapse explosively against a surface (C)</p> Signup and view all the answers

What is the primary cause of water hammer in process applications?

<p>Quick closing valve (B)</p> Signup and view all the answers

What effect does cavitation primarily have on a valve over time?

<p>Causes permanent deterioration of the valve's interior (B)</p> Signup and view all the answers

What is a cavitation index used for?

<p>To assess the severity of potential cavitation (B)</p> Signup and view all the answers

Which of the following can cause water hammer due to rapid valve closure?

<p>Valve slamming shut (A)</p> Signup and view all the answers

What is the maximum acceptable stroking duration for closing a valve?

<p>1 second multiplied by valve diameter (A)</p> Signup and view all the answers

How does increasing pressure affect the vapor bubbles in a cavitation scenario?

<p>It collapses the bubbles back to a liquid state (A)</p> Signup and view all the answers

What role does the flow velocity play in the cavitation process within a valve?

<p>Increased flow velocity leads to drop in pressure affecting cavitation (B)</p> Signup and view all the answers

What can be a consequence of water hammer in piping systems?

<p>Leaking connections (B)</p> Signup and view all the answers

What can be a direct consequence of cavitation occurring near a valve's surface?

<p>Erosion and material fatigue (D)</p> Signup and view all the answers

Which frequency range is most sensitive to human hearing?

<p>1000 – 8000 Hz (B)</p> Signup and view all the answers

Which method is effective in minimizing water hammer in valves?

<p>Slowly closing the valve (C)</p> Signup and view all the answers

What is the permissible noise level (dBA) for a duration of 4 hours?

<p>95 dBA (A)</p> Signup and view all the answers

Which of the following statements about cavitation is incorrect?

<p>Cavitation only occurs in high-temperature environments (C)</p> Signup and view all the answers

What effect does turbulence in valves typically have?

<p>Creates high noise levels (C)</p> Signup and view all the answers

What is one effect of low-frequency noise on humans?

<p>Fatigue in vital organs (B)</p> Signup and view all the answers

What can be done to handle unexpected surge in a fluid system?

<p>Inject gas to increase fluid compressibility (D)</p> Signup and view all the answers

Which of these factors is NOT a common consequence of water hammer?

<p>Decreased fluid temperature (D)</p> Signup and view all the answers

What is a benefit of upgrading the packing box in valve maintenance?

<p>It is usually more cost-effective than complete replacement. (A)</p> Signup and view all the answers

Which sealing method does not require continual retightening?

<p>Live-loading (A)</p> Signup and view all the answers

What is a primary motivation for addressing fugitive emissions in valve maintenance?

<p>Health and safety concerns (C)</p> Signup and view all the answers

What can cumulative and irreversible hearing damage begin with?

<p>Loss of high-frequency sound (C)</p> Signup and view all the answers

Which of the following equipment may be affected by valve performance issues due to noise and vibration?

<p>Nearby process equipment (D)</p> Signup and view all the answers

What is a common cause of leakage in a valve that has recently been repaired?

<p>Misalignment between the plug and seat (C)</p> Signup and view all the answers

Which of the following is NOT a potential cause of excessive wear on a valve seat?

<p>Poor lubrication (C)</p> Signup and view all the answers

What must be ensured before disassembling and reassembling a valve?

<p>Valve is free from pressure and working fluid (A)</p> Signup and view all the answers

What action should be taken if a leak persists after tightening the bolts?

<p>Check for damaged gasket or packing (A)</p> Signup and view all the answers

During troubleshooting of a valve, what is the recommended practice?

<p>Perform periodic inspections and troubleshoot during operation (A)</p> Signup and view all the answers

If a valve is used in a corrosive application, what should be done before maintenance?

<p>Decontaminate the valve (B)</p> Signup and view all the answers

Which condition can rarely cause damage to a valve's body or bonnet?

<p>Minor damage (A)</p> Signup and view all the answers

What should be done if there is evidence of foreign material between the gate and seat?

<p>Inspect and remove the foreign material (B)</p> Signup and view all the answers

Flashcards

Non-return Valve

A valve that allows fluid to flow in only one direction, preventing backflow.

Throttling Valve

A type of valve that regulates flow, temperature, or pressure.

Pressure Regulator

A special type of throttling valve that maintains constant pressure downstream.

Special Service Valve

A valve designed for a specific application with special requirements.

Signup and view all the flashcards

Severe Service Valve

A valve designed for demanding applications with extreme conditions.

Signup and view all the flashcards

General Service Valve

Valves that can handle most common applications without modifications.

Signup and view all the flashcards

Check Valve

A type of valve that allows fluid to flow in one direction while preventing backflow.

Signup and view all the flashcards

Automatic Control Valve

A valve that adjusts its position automatically to control flow conditions according to process needs.

Signup and view all the flashcards

Cavitation

The act of a liquid turning into a vapor because the pressure drops below its vapor pressure. It often happens quickly due to changes in flow velocity, for instance, through a valve.

Signup and view all the flashcards

Vena Contracta

The point where the flow area narrows the most during fluid flow through a valve.

Signup and view all the flashcards

Bubble Implosion

The process of cavitation bubbles collapsing as they move away from the vena contracta, creating pressure waves that erode valve surfaces.

Signup and view all the flashcards

Cavitation Index (σ)

A measure that indicates the potential for cavitation in a valve. It considers upstream pressure, downstream pressure, and vapor pressure.

Signup and view all the flashcards

Cavitation Damage

Cavitation can cause damage to the internal surfaces of a valve, leading to performance degradation.

Signup and view all the flashcards

Flow Characteristic Distortion

Cavitation can affect the flow characteristics of a valve, resulting in decreased performance and reduced efficiency in a system.

Signup and view all the flashcards

Material Fatigue

Caused by the implosion of vapor bubbles near the valve surface.

Signup and view all the flashcards

Vapor Pressure

The tendency of the liquid to create bubbles due to reduced pressure is called the vapor pressure. It depends on temperature.

Signup and view all the flashcards

Cavitation Index

A dimensionless number that quantifies the potential for cavitation in a valve. It is calculated based on upstream and downstream pressure, as well as vapor pressure.

Signup and view all the flashcards

Cavitation Index Criteria by Valve Type

The valve type determines the cavitation index thresholds for incipient and choked conditions. This table provides a good overview of the different valve types and their cavitation indices.

Signup and view all the flashcards

Incipient Cavitation

The point at which cavitation just begins to occur in a valve. The valve is still operating efficiently but the risk of damage is increasing.

Signup and view all the flashcards

Choked Cavitation

The point at which the valve is completely choked by cavitation. The flow is severely restricted, and the valve is at risk of damage.

Signup and view all the flashcards

Special Trim for Cavitation Prevention

Using special valve internals, such as a multi-stage trim, is a way to reduce the pressure drop across the valve, therefore lowering the cavitation index and preventing damage.

Signup and view all the flashcards

Air Injection for Cavitation Prevention

Injecting air into the flow stream can disrupt the imploding bubbles, reducing their destructive potential. This is particularly useful for large valves dumping into tanks.

Signup and view all the flashcards

Downstream Back Pressure for Cavitation Prevention

Increasing the downstream pressure help to reduce the pressure drop across the valve. This can be achieved with a downstream back pressure device.

Signup and view all the flashcards

Hardened Materials for Cavitation Prevention

Using materials with high hardness, typically Rockwell hardness 40 or higher, can help to resist the erosive effects of cavitation, extending valve life.

Signup and view all the flashcards

Water Hammer

A sudden pressure spike caused by the rapid stopping of fluid flow in a pipe, often due to valve closure.

Signup and view all the flashcards

Quick-Closing Valve

A valve that is designed to close quickly, causing a sudden stop in fluid flow and leading to water hammer.

Signup and view all the flashcards

Stroking Duration

The amount of time it takes for a valve to fully open or close. A longer stroking duration helps minimize water hammer.

Signup and view all the flashcards

Valve Actuator

A device that slows the closure of a valve to reduce the sudden change in pressure and prevent water hammer.

Signup and view all the flashcards

Effects of Water Hammer

The potential problems caused by water hammer, such as ruptured pipes, leaking connections, and damaged equipment.

Signup and view all the flashcards

Surge Protection Devices

Devices designed to absorb sudden pressure surges and prevent water hammer by releasing excess pressure.

Signup and view all the flashcards

Gas Injection

The addition of gas into a system to reduce the impact of water hammer by making the fluid more compressible.

Signup and view all the flashcards

Valve Noise

Turbulence created by valve geometry that generates loud noises in the downstream piping.

Signup and view all the flashcards

Most damaging noise frequency range for humans

Noise with frequencies between 1000 and 8000 Hz is most damaging to human hearing.

Signup and view all the flashcards

Noise-induced hearing loss

Exposure to high-intensity noise can lead to permanent hearing loss.

Signup and view all the flashcards

Harmful noise level for hearing

Noise levels exceeding 100 dBA can be harmful to human hearing.

Signup and view all the flashcards

Lower-frequency noise effects

Lower-frequency noise can negatively impact the function of internal organs like the heart and liver.

Signup and view all the flashcards

Packing box upgrades for valve sealing

Continuously monitored packing requires more effort and attention.

Signup and view all the flashcards

Live-loading for valve sealing

Live-loading maintains constant pressure on packing without requiring frequent adjustments.

Signup and view all the flashcards

Metal-bellows seal for valve sealing

Metal bellows seals provide complete leak prevention in linear valves.

Signup and view all the flashcards

Fugitive emissions

Fugitive emissions are leaks of gases or liquids from equipment like valves, sensors, or regulators.

Signup and view all the flashcards

Excessive Valve Leakage

Excessive wear on the seat ring-plug is a likely cause of excessive leakage in a valve, even after maintenance according to the manual.

Signup and view all the flashcards

Causes of Valve Seat Wear

Erosion, corrosion, cavitation, and flashing are common reasons for excessive wear on the valve seat ring-plug.

Signup and view all the flashcards

Valve Misalignment

Misalignment between the plug and seat is a frequent reason for leakage in a newly repaired valve.

Signup and view all the flashcards

Valve Disassembly Safety

Before disassembling and reassembling a valve, ensure it is free of pressure and working fluids.

Signup and view all the flashcards

Valve Decontamination

Decontaminate valves used with corrosive, toxic, or caustic substances before handling to prevent harm to personnel or equipment.

Signup and view all the flashcards

Valve Installation Procedure

After repairing a valve, install it as explained in the procedures.

Signup and view all the flashcards

Gate Valve Troubleshooting

Regularly inspect and troubleshoot gate valves for potential issues. This can often be done while the valve is operational.

Signup and view all the flashcards

Gate Valve Leakage

If leakage occurs in a gate valve, tighten the bolts as per the procedure. If leakage persists, inspect and potentially repair the gasket or packing.

Signup and view all the flashcards

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.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Valve Maintenance PDF

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.

More Like This

Distributor Valve Functions Quiz
5 questions

Distributor Valve Functions Quiz

NoteworthyHappiness9933 avatar
NoteworthyHappiness9933
The Heart: Function Quiz
12 questions

The Heart: Function Quiz

BrightestVuvuzela avatar
BrightestVuvuzela
Pump & Compressor System Components
40 questions

Pump & Compressor System Components

WealthySydneyOperaHouse3045 avatar
WealthySydneyOperaHouse3045
2 Plumbing System Essentials Quiz
62 questions

2 Plumbing System Essentials Quiz

AdvancedCourage8795 avatar
AdvancedCourage8795
Use Quizgecko on...
Browser
Open
Browser
Browser