If the minimum pump suction pressure is below what psi, a compound pressure and vacuum gauge must be used?

The requirement for using a compound pressure and vacuum gauge arises from the need to accurately measure both positive pressure and vacuum conditions in pumping systems. If the minimum pump suction pressure falls below 20 psi, a standard pressure gauge might not provide sufficient accuracy, particularly when it comes to measuring negative pressure (vacuum). A compound gauge is specifically designed to measure pressures below atmospheric levels, which is essential in applications involving low suction pressures.

Utilizing a compound gauge in situations where the suction pressure is below 20 psi ensures that both the vacuum conditions and any positive pressures are accurately represented, preventing damage to equipment and ensuring safe operation. This level is established to enhance system reliability and operator safety, thus making it critical for all installers and technicians to adhere to this standard.