Security lock assembly for shut-off valve

A security lock assembly for a shut-off valve consisting of a valve body and an exterior engageable portion secured to a gate stem so as to rotate said stem, said body having a flange with a hole therein, said security lock assembly comprising:

• a lock disk having a central opening for receiving said engageable portion, abutment edges formed integrally with said disk for engagement with said engageable portion so as to rotate therewith, and a series of indentations formed in a bottom surface of said lock disk at a predetermined position and disposed in an arcuate section on said lock disk;
• a pin-lock assembly retained in said hole of said flange of said valve body, said pin-lock assembly having a pin portion upwardly biased against said lock disk, said pin portion being aligned with said indentations so as to engage therein when said valve stem is rotated to a predetermined closed position, whereby said valve is locked in said predetermined closed position by said pin portion, said pin portion preventing said valve from being turned in a valve opening direction and allowing said valve to be turned in a valve closing position.