Section Three Valves

Question 1

What is the primary function of a valve?

Answer 1

To start, stop, or regulate the flow of a fluid in a piping system.

Question 2

What are the main categories of valves?

Answer 2

Stop valves, check valves, throttling valves, and special-purpose valves.

Question 3

What is a stop valve?

Answer 3

A valve designed to completely shut off flow when closed.

Question 4

What is a throttling valve?

Answer 4

A valve designed to control or regulate flow rate.

Question 5

What is a check valve?

Answer 5

A valve that allows flow in one direction only and prevents backflow.

Question 6

What is the most common type of stop valve?

Answer 6

The gate valve.

Question 7

How does a gate valve operate?

Answer 7

By raising or lowering a gate (wedge) between the seats to open or close flow.

Question 8

Should gate valves be used for throttling?

Answer 8

No, they should be fully open or fully closed to prevent seat and gate damage.

Question 9

What are the main types of gate valves?

Answer 9

Solid wedge, flexible wedge, split wedge, and double-disc.

Question 10

What is a globe valve?

Answer 10

A valve with a disc that moves perpendicular to flow, designed for throttling or regulating flow.

Question 11

Where is a globe valve commonly used?

Answer 11

Where frequent flow regulation is needed, such as in steam lines or cooling systems.

Question 12

What are the flow characteristics of a globe valve?

Answer 12

They cause more pressure drop than a gate valve due to the tortuous flow path.

Question 13

What is an angle valve?

Answer 13

A variation of the globe valve with the outlet at 90 degrees to the inlet.

Question 14

What is a ball valve?

Answer 14

A valve that uses a spherical ball with a hole through it to control flow.

Question 15

What is the advantage of a ball valve?

Answer 15

Quick quarter-turn operation with tight shutoff and minimal pressure drop.

Question 16

What is a butterfly valve?

Answer 16

A valve with a rotating disc mounted on a shaft that opens or closes the flow with a quarter turn.

Question 17

What are butterfly valves commonly used for?

Answer 17

Large-diameter, low-pressure systems like HVAC or water service.

Question 18

What is a plug valve?

Answer 18

A valve that uses a cylindrical or tapered plug with a passageway to control flow.

Question 19

What is a needle valve?

Answer 19

A small valve with a tapered, needle-like stem for precise flow control.

Question 20

Where are needle valves commonly used?

Answer 20

Instrumentation, calibration, and fine adjustment applications.

Question 21

What is a diaphragm valve?

Answer 21

A valve using a flexible diaphragm pressed against a seat to stop flow.

Question 22

What type of service is a diaphragm valve ideal for?

Answer 22

Corrosive, dirty, or slurry service because the fluid doesn’t contact moving parts.

Question 23

What is a check valve used for?

Answer 23

To prevent backflow in piping systems.

Question 24

Name common types of check valves.

Answer 24

Swing, lift, ball, and spring-loaded check valves.

Question 25

How does a swing check valve operate?

Answer 25

A hinged disc swings open with flow and closes automatically with reverse flow.

Question 26

How does a lift check valve operate?

Answer 26

A disc or piston lifts off the seat with forward flow and reseats with backflow.

Question 27

What is a relief valve?

Answer 27

A valve that automatically opens to relieve excess pressure.

Question 28

What is the difference between a relief valve and a safety valve?

Answer 28

A safety valve opens fully and instantly at a set pressure (steam/gas), while a relief valve opens gradually (liquid service).

Question 29

What is a pressure-reducing valve?

Answer 29

A valve that maintains a constant downstream pressure regardless of inlet pressure fluctuations.

Question 30

What is a foot valve?

Answer 30

A check valve installed at the bottom of a suction line to retain prime in pumps.

Question 31

What is a solenoid valve?

Answer 31

An electrically operated valve using a magnetic coil to open or close the flow.

Question 32

What should be considered when selecting a valve?

Answer 32

Type of service, operating pressure and temperature, flow characteristics, and maintenance needs.

Question 33

What are common end connections for valves?

Answer 33

Threaded, flanged, soldered, socket-weld, and butt-weld ends.

Question 34

What is a valve body made from for general service?

Answer 34

Brass, bronze, cast iron, or steel depending on application.

Question 35

What is a stem in a valve?

Answer 35

The component that transmits motion from the handwheel or actuator to the disc, gate, or plug.

Question 36

What is packing in a valve?

Answer 36

Material around the stem that prevents leakage through the bonnet.

Question 37

What is the bonnet of a valve?

Answer 37

The top cover that encloses the stem and packing assembly.

Question 38

What is a valve seat?

Answer 38

The surface against which the closure element seals to stop flow.

Question 39

What is the function of an actuator?

Answer 39

A device that automatically operates a valve using air, electricity, or hydraulics.

Question 40

What is a manual valve?

Answer 40

A valve operated by handwheel, lever, or wrench.

Question 41

What does “fail-safe” mean in valve systems?

Answer 41

The valve moves to a predetermined safe position (open or closed) upon power or signal loss.