Test 3

Question 1

What is a final element?

Answer 1

A device that receives a control signal and regulates the amount of material energy in a process.

Question 2

How are the valve flow characteristics represented graphically?

Answer 2

Percent flow vs percent open

Question 3

3 Valve flow characteristics

Answer 3

1. Quick-opening valve
2. Linear Valve
3. Equal-percentage valve

Question 4

List and explain two phenomena that affect the control valves in liquid services.

Answer 4

1. Flashing - Liquid to vapor during pressure drops

2. Cavitation - Vapor bubbles in liquid collapse inside a valve as pressure increases.

Question 5

What is critical pressure ratio?

Answer 5

The ratio of downstream pressure to upstream pressure where gas out of a valve is at sonic velocity.

Question 6

Cv

Answer 6

Valve coefficient, Q x √p/ΔP

Question 7

What is the advantage of using a double ported valve over a single port valve?

Answer 7

Double ported valve reduces the force on the valve plug.

Question 8

Name four types of rotary shaft valves

Answer 8

1. Butterfly
2. Ball
3. Plug
4. Eccentric Cam Control Valve

Question 9

What is the difference between a pressure regulator and a back pressure regulator?

Answer 9

Pressure regulator monitors downstream pressure, while a back pressure regulator monitors upstream pressure.

Question 10

List and Explain three types of dampers.

Answer 10

1. Parallel-blade Damper - A damper with adjacent blades that are in parallel.
2. Opposed-blade Damper - Damper, parallel blades, move in opposite direction.
3. Round-blade Damper - Damper that has a circular blade.

Question 11

List four requirements of an actuator.

Answer 11

Speed
Power
Precision
Resolution

Question 12

List four types of actuators used on control valves.

Answer 12

1. Diaphragm and Spring Actuator
2. Pneumatic Sliding Stem Piston Actuator
3. Pneumatic Rotary Piston Actuator
4. Electric Actuator

Question 13

What is the key feature of a typical valve positioner that allows for accurate positioning?

Answer 13

Feedback

Question 14

Give two examples of processes that would use split range control.

Answer 14

1. pressure control

2. Heating and cooling control valves

Question 15

List and Explain the four types of pressure regulators.

Answer 15

1. Spring-Loaded Pressure Regulator - Valve plug that is controlled by spring opposition.
2. Air-Loaded Pressure Regulator - Uses air pressure to oppose and control downstream pressure.
3. Pilot-Operated Pressure Regulator - Uses upstream fluid pressure to power the diaphragm of a larger valve.
4. Differential Pressure Regulator - Controls pressure difference between the outlet pressure and inlet pressure.