Valves

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Questions and Answers

What is a primary function of a ball valve?

On/Off flow control (correct)

Pressure regulation

Temperature regulation

Accurate flow rate control

What happens when you rotate a ball valve by 90 degrees?

The valve partially opens

The flow is completely stopped (correct)

The valve provides a continuous flow

The valve converts to a butterfly valve

Which of the following about ball valves is NOT true?

They are simple to operate

They require regular lubrication (correct)

They provide an excellent seal

They can be used with corrosive materials

In what scenario is using a ball valve potentially hazardous?

When accurate flow control is required Signup and view all the answers

Which material is frequently used to construct the ball in a ball valve to handle corrosive fluids?

PTFE Signup and view all the answers

Which category do ball valves belong to?

Rotating Stem Valves Signup and view all the answers

What is a disadvantage of using a ball valve?

Product can be trapped behind the ball Signup and view all the answers

What type of pipe applications are butterfly valves mainly used for?

Large diameter pipelines for controlling gas and steam Signup and view all the answers

What is a key advantage of diaphragm valves?

They have a streamlined flow path and minimal contact surfaces. Signup and view all the answers

Which type of diaphragm valve is best suited for high flow, slurry applications?

Straightway diaphragm valve Signup and view all the answers

What is a disadvantage of using diaphragm valves?

They are not suitable for high temperature or pressure applications. Signup and view all the answers

Which statement accurately describes non-return valves?

They prevent backflow of fluids by closing when flow stops. Signup and view all the answers

What is the primary function of a shuttle valve?

To alter the direction of flow between two ports. Signup and view all the answers

In terms of valve types, what is a key feature of check valves?

They may be spring-loaded to require specific pressure for operation. Signup and view all the answers

Which valve type is less effective as a control valve compared to globe-type control valves?

Weir style diaphragm valves Signup and view all the answers

What is the primary reason diaphragm valves are considered effective in preventing contamination?

They feature minimal contact surfaces and no cavities. Signup and view all the answers

What is the main operation method of a butterfly valve?

Rotating through 90 degrees Signup and view all the answers

What is a significant disadvantage of butterfly valves?

Potential for leaks when not locked Signup and view all the answers

Which type of valve is well-suited for applications requiring cleanliness and chemical compatibility?

Diaphragm valve Signup and view all the answers

How do reciprocating stem valves provide a tight seal?

By traveling perpendicularly to the valve seat Signup and view all the answers

What happens when a butterfly valve is fully closed?

It is at right angles to the flow Signup and view all the answers

Which statement is true regarding double seated sliding stem globe valves?

They may require regular seal replacement. Signup and view all the answers

What is a common hazard associated with butterfly valves?

Bacterial growth due to trapped products Signup and view all the answers

How do you achieve flow control with reciprocating stem valves?

By increasing or decreasing the orifice size Signup and view all the answers

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.