Pipefitter Pipe Systems and Fluid Mechanics 4 — Questions and Answers
Question 1: In a piping system, cavitation is most likely to occur at which location?
- At the pump discharge
- At the pump suction where pressure drops below vapor pressure (Correct answer)
- In long horizontal pipe runs
- At pipe elbows where velocity decreases
Correct answer: At the pump suction where pressure drops below vapor pressure
Cavitation occurs at the pump suction side when local pressure falls below the fluid's vapor pressure, causing vapor bubbles to form and collapse.
Question 2: What does the term 'hydraulic gradient' describe in a piping system?
- The slope of the pipe installation
- The rate of pressure drop per unit length of pipe (Correct answer)
- The velocity change across a pipe diameter
- The ratio of static to dynamic pressure
Correct answer: The rate of pressure drop per unit length of pipe
The hydraulic gradient represents the rate of pressure head loss per unit length along a pipe, indicating how pressure decreases due to friction.
Question 3: When two pipes of different diameters are joined in series, which parameter remains constant throughout?
- Velocity
- Pressure
- Volumetric flow rate (Correct answer)
- Reynolds number
Correct answer: Volumetric flow rate
By the continuity equation, volumetric flow rate (Q = A × V) remains constant in series piping, though velocity changes with cross-sectional area.
Question 4: A pipe system experiences water hammer. Which device is BEST suited to protect against this condition?
- A check valve
- A pressure relief valve
- A surge suppressor or accumulator (Correct answer)
- A flow control valve
Correct answer: A surge suppressor or accumulator
Surge suppressors and accumulators absorb the sudden pressure spike of water hammer by providing a compressible cushion in the system.
Question 5: In fluid mechanics, what is the significance of a Reynolds number greater than 4000?
- Flow is laminar and smooth
- Flow is in a transitional phase
- Flow is fully turbulent (Correct answer)
- Flow has reached critical velocity and will reverse
Correct answer: Flow is fully turbulent
A Reynolds number above 4000 indicates fully turbulent flow, where fluid moves in irregular, chaotic eddies rather than smooth layers.
Question 6: What is the primary purpose of an expansion loop in a steam piping system?
- To increase flow velocity
- To allow thermal expansion and contraction without stressing pipe joints (Correct answer)
- To reduce pressure in the line
- To trap condensate at low points
Correct answer: To allow thermal expansion and contraction without stressing pipe joints
Expansion loops provide flexibility to absorb the dimensional changes caused by thermal expansion and contraction, protecting joints and supports from stress.
Question 7: According to Bernoulli's principle, if fluid velocity increases in a pipe constriction, what happens to static pressure?
- Static pressure increases
- Static pressure remains unchanged
- Static pressure decreases (Correct answer)
- Static pressure fluctuates randomly
Correct answer: Static pressure decreases
Bernoulli's principle states that increased fluid velocity results in decreased static pressure, as kinetic energy increases at the expense of pressure energy.
Pipefitter Pipe Systems and Fluid Mechanics 4
In a piping system, cavitation is most likely to occur at which location?