The method
Before using the result
- Use consistent fluid properties at the operating temperature. Results do not select equipment or establish code compliance.
- Efficiencies must be greater than zero and no more than 100%.
Worked examples
These original training examples illustrate the method for California SWRCB Water Distribution Operator D1. Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Distinguish water power, pump shaft power and electrical input in a distribution-system calculation. Apply pump and motor efficiencies in the correct order.
- Volume flow
- 2 L/s
- Total dynamic head
- 30 m
- Fluid density
- 1,000 kg/m³
- Pump efficiency
- 75 %
- Motor efficiency
- 90 %
- Ph = 1000 × 9.80665 × 0.002 × 30 = 588.399 W.
- Pshaft = 588.399 / 0.75; Pelectric = Pshaft / 0.9.
- Hydraulic power: 588.399 W
- Shaft power: 784.532 W
- Electrical power: 871.7022 W
2. Comparison example
Compare a different supplied condition using the same method. For Water Certification Exam, the important check is that the input meaning, units and method assumptions still match the problem.
- Volume flow
- 2 L/s
- Total dynamic head
- 40 m
- Fluid density
- 1,000 kg/m³
- Pump efficiency
- 75 %
- Motor efficiency
- 90 %
- Ph = 1000 × 9.80665 × 0.002 × 40 = 784.5319999999999 W.
- Pshaft = 784.5319999999999 / 0.75; Pelectric = Pshaft / 0.9.
- Hydraulic power: 784.532 W
- Shaft power: 1,046.043 W
- Electrical power: 1,162.27 W
Check your understanding
1. Which relationship is used?
Hydraulic power = ρgQH; shaft power = hydraulic/ηpump; electrical power = shaft/ηmotor.
2. Which assumption should you check first?
Use consistent fluid properties at the operating temperature. Results do not select equipment or establish code compliance.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
This tool connects to California SWRCB Water Distribution Operator D1 free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.