WTO Water Distribution & Storage Systems 3 — Questions and Answers
Question 1: A water hammer event in a distribution system is best described as:
- Gradual pressure loss due to pipe corrosion
- A sudden pressure surge caused by rapid changes in flow velocity (Correct answer)
- Chemical scaling on valve seats
- Vibration from a misaligned pump impeller
Correct answer: A sudden pressure surge caused by rapid changes in flow velocity
Water hammer occurs when flow is suddenly stopped or reversed, creating a shock wave of high pressure that can damage pipes, valves, and meters.
Question 2: Which device is installed at a customer service connection to allow the utility to shut off water supply without entering private property?
- Corporation stop
- Curb stop (Correct answer)
- Gate valve
- Check valve
Correct answer: Curb stop
A curb stop (or curb valve) is located at the property line and allows the utility to control the customer's service without accessing the private side.
Question 3: What is the purpose of a blow-off assembly at a low point in a water main?
- Introduce chlorine for disinfection
- Allow air to escape when filling the main
- Drain the main for maintenance or flushing (Correct answer)
- Measure flow velocity
Correct answer: Drain the main for maintenance or flushing
Blow-off assemblies are installed at low points to drain sediment, standing water, or the full main volume during maintenance operations.
Question 4: Fire hydrant flow testing is conducted primarily to:
- Measure chlorine residual at the hydrant
- Determine available flow and residual pressure for fire suppression (Correct answer)
- Check for cross-connections in the service area
- Identify leaking service lines
Correct answer: Determine available flow and residual pressure for fire suppression
Hydrant flow tests measure residual pressure and flow rate to verify adequate fire protection capacity is available in that area of the distribution system.
Question 5: The C-factor in the Hazen-Williams equation represents:
- Cross-sectional area of the pipe
- Roughness coefficient of the pipe interior (Correct answer)
- Concentration of chlorine residual
- Cubic feet per second of flow
Correct answer: Roughness coefficient of the pipe interior
The C-factor (Hazen-Williams roughness coefficient) reflects the smoothness of a pipe's interior; higher values indicate smoother pipes with less friction.
Question 6: Air release and vacuum breaker valves are installed at high points in a pipeline because:
- Pressure is highest at elevated points and needs relief
- Air accumulates at high points and can restrict flow or cause negative pressure (Correct answer)
- Chlorine residual is lowest at high points
- Meters are less accurate at high elevations
Correct answer: Air accumulates at high points and can restrict flow or cause negative pressure
Air naturally migrates to high points; trapped air reduces flow capacity and negative pressure during draining can collapse flexible mains if not vented.
Question 7: A distribution system leak detection survey using acoustic correlators primarily detects leaks by:
- Measuring pressure drops along the main
- Detecting the sound frequency of water escaping under pressure (Correct answer)
- Monitoring chlorine residual changes between zones
- Using infrared cameras to find temperature differences
Correct answer: Detecting the sound frequency of water escaping under pressure
Acoustic correlators identify leaks by analyzing the sound vibration of pressurized water escaping from a pipe and triangulating the leak location.
WTO Water Distribution & Storage Systems 3
A water hammer event in a distribution system is best described as: