1. small valves used to drain or release fluid from a system, especially in engines or radiators
Usage: mechanical; automotive

Examples

• The mechanic opened the petcocks to drain the coolant from the radiator.
• Make sure to close all petcocks before refilling the system.
• The engine block has several petcocks for maintenance purposes.
• He turned the petcock counterclockwise to release the trapped air.
• The old tractor’s petcocks were rusted and needed replacement.
• Check the petcocks regularly to prevent fluid leaks.