Chapter 2
Valves
OBJECTIVES
After studying this chapter, the student will be able to:
▪ Explain the purpose of valves in industrial manufacturing.
▪ Identify the basic components of a gate valve.
▪ Identify the basic components of a globe valve.
▪ Explain the operation and design of a ball valve.
CHAPTER 2 REVIEW QUESTIONS
1. List the three basic types of actuators and explain how each works. Answer: Actuators
come in three basic designs: pneumatically (air) operated, electrically operated, and
hydraulically operated. Pneumatically operated actuators are the most common type.
They come in three designs: diaphragm, piston, and vane. Each design converts air
2. List the information found on the bridgewall markings. Answer: The body of the valve
contains bridgewall markings, which provide manufacturer information specific to the
valve. The bridgewall markings include the following letters and symbols:
W = Low-temperature water service
3. List the basic components of a gate valve.
4. Compare a gate valve and its function to a globe valve.
Answer: Gate valves are primarily used for on/off service, while a globe valve is
5. Identify the three most common gate (flow element) designs.
6. List the two gate valve designs and explain how each works.
Answer: The stem on a gate valve comes in two designs: rising stem and nonrising stem.
Located at the top of the gate valve is the handwheel. The handwheel is attached to a
7 . Globe valves are primarily used for what type of service?
8. Describe the flow of fluid through a globe valve.
Answer: A globe valve places a movable metal disc in the path of a process flow. This
9. Describe quick opening or quarter turn valves.
Answer: Ball valves, plug valves, butterfly valves, are classified as quick opening or
10. Describe the operation and design of a diaphragm valve. Answer: Diaphragm valves use
a flexible membrane and seat to regulate flow. The handwheel operates just like the
handwheel on a gate or globe valve. The stem is attached to a device called the
compressor. The compressor pushes on a flexible diaphragm. The internal parts of the
11. Compare a relief valve to a safety valve and describe how each works.
Answer: Relief valves are engineered to work with liquids while safety valves work to
relieve pressure in gas systems. A relief valve is designed to open at a predetermined
12. List the four types of check-valves and explain how the device
works? Answer: Swing check, lift check, ball check, stop check. Check valves are
13. A butterfly valve can be used for what type of service? Answer: Butterfly valves are
14. Explain a process technician’s role in maintaining and operating valves.
Answer: Maintaining equipment is an important part of an operator’s job. Valve stem
threads exposed to weather need to be lubricated with antiseize compound to keep them
15. List the four common disc designs used with globe valves. Answer: Plug, needle,
16. Compare and contrast the operation of a weir and non-weir
diaphragm valve. Answer: Diaphragm valves come in two designs: weir and nonweir.
The weir diaphragm valve has a weir (a dam) located in the body of the valve (Figure
17. Describe the term, accumulation. Answer: Relief valves vary in design and style. Relief
18. List the basic components of a control loop. Answer: The chemical processing industry
uses a complex network of automated instrument systems to control its processes. The
19. Describe the three types of pneumatic actuators. Answers: They come in
three designs: diaphragm, piston, and vane. Each design converts air pressure to
mechanical energy. The diaphragm actuator is a dome-shaped device that has a flexible
20. Describe the design and operation of a solenoid valve. Answer: The internal structure of a
solenoid resembles that of a globe valve (Figure 2.27). The disc rests in the seat, stopping