Abstract: A lockable hydraulic valve for preventing unauthorized use of a system, machinery item or vehicle requiring operation by both electric and hydraulic circuits. The valve comprising a housing provided with a spool bore and at least one hydraulic inlet and at least one hydraulic outlet. A spool allows oil passage from inlet to outlet in a first spool position. A key can drive the spool 90 degrees from a second, locked position to a first open position. A lock member in a hollow provided in the solid housing, engages and revolves the spool and also serves to block access to the exposed end of the spool. A locator member prevents axial movement of the spool member and locates in a spool groove. A non-central spool projection projects outward and operates at least one electric switch to immobilize at least one essential electric circuit simultaneously to the blocking of oil flow.