1. n. [Well Completions]

A device that is operated to equalize the pressure across a valve, plug or similar pressure or fluid isolation barrier. The operating mechanism on many pressure-sealing devices is rendered inoperable once the mechanism has been activated by pressure. In such cases, the pressure across the pressure barrier must be equalized before the barrier can be removed.

2. n. [Well Workover and Intervention]

A high-pressure valve, generally of small diameter, located on a conduit that runs between the two sides of an isolation valve or blowout preventer ram set. The forces acting on isolation devices such as blowout preventer rams can be extremely high, preventing the rams from being opened, or causing damage to the ram set seals during the opening process. The equalizing valve allows the pressure to be equalized across the ram set or isolation valve, enabling the device to be opened safely.

See: blowout preventer