The prior art is already aware of safety mechanisms, such as safety controls, for use in hydraulic equipment wherein the hydraulic line is broken or the hydraulic pump is turned off.  One such example of a control is shown in U.S. Pat.  No.  2,964,016, and that patent is showing apparatus useful in retaining a lifted load in an elevated position even though the hydraulic pressure is inadvertently reduced.  The present invention is an improvement upon this type of apparatus, and it accomplishes the arrangement of a hydraulic safety system which is self-actuating and is reliable and operative in the event that the hydraulic pressure is inadvertently reduced, and the lifted load or the like wll not be immediately released in response to the reduced hydraulic pressure. 
Another object of this invention is to provide a hydraulic safety system which is simplified in its apparatus and in its installation, and to provide one which can be readily and easily installed in a hydraulic system and is constantly available and is reusable for locking the system in an operative position when the hydraulic pressure is inadvertently reduced, such as by having a hydraulic line break.  As such, the present invention provides a fail-safe system, for the purposes mentioned above. 
Still further, the present invention provides a hydraulic safety system which is automatically operative, under the conditions and for the reasons mentioned above, and one which can also be manually operated to release it from a locked position wherein the work load is being supported even though the hydraulic line or the like has failed to retain hydraulic pressure.  In accomplishing this object, the manual release is arranged so that it can be operated to gradually release the hydraulic pressurizing and sustaining of the lifted load, for instance, and thus the safety lock or like element of this invention provides for automatic safety and also for controlled manual release of same. 
Other objects and advantages will become apparent upon reading the following description in light of the accompanying drawings.