Massachusetts Plumbers Journeyman Practice Exam

At what pressure should a completed water supply system be tested for tightness?

1. 50 pounds per square inch

2. 75 pounds per square inch

3. 100 pounds per square inch

4. 125 pounds per square inch

The correct answer is: 125 pounds per square inch

A completed water supply system should be tested for tightness at a pressure of 125 pounds per square inch. This standard testing pressure ensures that the system can withstand operational pressures and checks for leaks or weaknesses in the installation. Testing at this level helps to confirm that connections, fittings, and materials used in the system are secure and that there are no potential failures that could lead to leaks during normal operation. Testing at lower pressures, such as 50, 75, or 100 pounds per square inch, may not adequately identify all potential issues within the system, since it could potentially mask problems that might only become apparent at the higher operational pressures that the system will face in everyday use. Therefore, using 125 psi for the tightness test aligns with safe practices to ensure the reliability and integrity of the plumbing system.