Abstract: A rotary plug valve is disclosed having a housing and a valve core which can be selectively locked in an unlimited number of positions relative to the mandatory inlet and outlet piping, said valve having no visible indication of the internally concealed locking mechanism location. Selectively, a locking pin, that can be activated by authorized personnel, is passed through a passageway engaging a concealed locking cap preventing rotation of the valve core relative to the valve housing for security and safety applications. Removal of the locking pin with an authorized key permits operation for conventional usages.