CSLB C-46 Solar ContractorSolar Thermal System InstallationMedium
A solar thermal system installer is replacing an old pump with a new one in a closed-loop system. After installation, the installer notices excessive noise and vibration originating from the pump. Which of the following is the MOST likely cause of this issue?
- AThe system pressure is too high, causing cavitation.
- BThe pump is undersized for the system's head requirements.
- CAir is trapped in the pump volute or suction line.
- DThe pump motor is improperly grounded.
Show answer & explanationAnswer & explanation
Correct answer: C. Air is trapped in the pump volute or suction line.
Trapped air in the pump volute or suction line is a very common cause of pump noise, vibration, and cavitation-like symptoms, as the pump struggles to move a mixture of air and fluid. Proper purging of air during startup is critical.
Why the other options are wrong
- A. High system pressure would reduce the likelihood of cavitation, which is caused by low pressure (vaporization).
- B. An undersized pump would result in low flow, but not necessarily excessive noise and vibration unless it's severely struggling against high head, which is less common than air.
- D. Improper grounding would be an electrical safety hazard, not typically a direct cause of mechanical noise and vibration.
Pump Noise/Vibration Causes
Common issues leading to undesirable noise and vibration in hydronic circulation pumps.
- Air in the system is a primary culprit.
- Can also be caused by cavitation, misalignment, or mechanical wear.
- Requires systematic troubleshooting for resolution.
Memory trick: When the pump makes a ruckus and a hum, check for air, it's often the drum!