Journeyman Plumber ExamWater Supply SystemsMedium
A plumber is testing a newly installed water distribution system in a multi-story building. The system is pressurized to 100 psi for the test. However, after 30 minutes, the pressure gauge reading has dropped to 95 psi, with no visible leaks. What is the most likely cause of this pressure drop without visible water leakage?
- AA major pipe burst in an inaccessible wall cavity.
- BRapid consumption of water by unclosed fixtures.
- CA faulty pressure gauge providing an inaccurate reading.
- DTemperature decrease in the water within the piping system.
Show answer & explanationAnswer & explanation
Correct answer: D. Temperature decrease in the water within the piping system.
When water in a sealed system cools, its volume decreases, leading to a corresponding drop in pressure. This is a common occurrence during pressure testing, especially if the initial pressurization was done with warmer water or if the ambient temperature drops during the test.
Why the other options are wrong
- A. A major pipe burst would result in a significant and rapid pressure drop, along with visible signs of water damage.
- B. Rapid consumption of water by unclosed fixtures would lead to a very quick and significant pressure drop, and the test should not be conducted with open fixtures.
- C. While possible, a faulty gauge would likely give inconsistent readings or be permanently off, not a gradual, consistent drop without other signs.
Water Pressure Test Drop (No Leak)
A common phenomenon during water system pressure testing where a slight pressure drop occurs in the absence of visible leaks, usually due to water temperature changes.
- Water contracts when it cools
- Causes pressure drop in sealed system
- Not indicative of a leak if minor and gradual
- Allow system to stabilize before final reading
Memory trick: Pressure drop, no drip? Check the temp, it's a cooling trip!