Jack safety device

A safety device on a jack which has a hydraulic cylinder and a hydraulic stem shaft extending into the hydraulic cylinder, the safety device comprising:

• coupling grooves provided in a row on a horizontal length of the hydraulic stem shaft extending into the hydraulic cylinder;
• a hollow set key lid mounted on a hole forming an entrance to the hydraulic stem shaft in the hydraulic cylinder;
• a spanner positioned on said hollow set key lid and having a bearing surface in camming contact with said hollow set key lid;
• a stop rotation key having one end for abutting in said coupling grooves and another end for pivotal attachment to said spanner
• a spring positioned with said hollow set key lid to oppose a withdrawal action of said stop rotation key from said coupling grooves;
• said stop rotation key and said spanner connected eccentrically relative to said bearing surface camming contact to cause a lifting of said stop rotation key out of said grooves upon movement of the opposite end of said spanner from the connection to said key in a direction towards the hydraulic cylinder and a movement of said key into said grooves under action of said spring upon release of said opposite end of said spanner in a direction away from the hydraulic cylinder;
• and
• a propelling stem shaft demountably connected to said spanner and said key with a quick pin sliding in a groove connect and disconnect structure.