Many hydraulic hammers have a hydraulic chamber which receives pressurized fluid from a hydraulic pump for moving a piston in a direction against a volume of compressible gas.  Once the piston reaches a predetermined position, an actuating valve is automatically sequenced to a position for venting the hydraulic chamber, thereby allowing the compressed gas to rapidly propel the piston in an opposite direction against a cutting tool.  The actuating valve of some of those hammers blocks the flow of fluid from the pump to the hammer during the propelling stroke of the piston.  When this happens, the pressurized fluid is commonly relieved by a relief valve connected to the pump output conduit.  This reduces the efficiency of the operation in several ways.  First of all, since the pressure relieving setting of the relief valve must be higher than the normal operating pressure of the hammer, considerable energy must be expended to pump the fluid through the relief valve at such high pressure.  Secondly, since the operating speed of the hammer is dependent upon the pump output, a larger pump is required since some of the pressurized fluid is not being utilized in the actual operation of the hammer. 
One prior art reference relating to this general subject is U.S. Pat.  No.  4,715,265, issued Dec. 29, 1987 to Graul et al.  That system relates to an apparatus for vibratory operation of a working piston in which the piston is moved toward the tool by pressurized hydraulic fluid from a pump through an actuating valve.  The actuating valve has an inlet port connected to the pump and alternately establishes and blocks communication of fluid through the valve from the pump to the actuating chamber.  A pressure equalizing storage means or reservoir is also connected to the inlet port of the actuating valve.  However, that reference fails to provide any functional use for such pressure equalizing storage means. 
The present invention is directed to overcoming one or more of the above problems.