Hydraulically driven hammer system

In a hydraulically driven hammer system a hydraulic piston and cylinder assembly means including a hydraulic valve for actuating said assembly for causing reciprocal relative movement between the piston and cylinder thereof, a support frame connected to a stationary part of said piston and cylinder assembly, a massive ram connected to a movable part of said piston and cylinder assembly, said massive ram being guided by said frame for reciprocal relative movement therein, said hydraulic valve having a fluid operated pilot which switches the valve in response to the application thereto of a given pressure, pilot means which controls operation of said hydraulic valve in response to movements of said ram, said pilot means comprising a land and means forming a surface over which the land moves, said land and said surface cooperating to separate a region of said given pressure from a region of different pressure, a pilot conduit having an opening onto said surface and extending therefrom to said fluid operated pilot, a said land and said means forming said surface being relatively movable upon movement of said ram with respect to said frame so that said land covers and uncovers said pilot opening and alternately exposes said pilot opening to said region of given pressure and said region of different pressure, and a restrictive flow conduit extending from said source of different pressure to said pilot while said land covers said conduit and until said pilot opening becomes exposed to said source of given pressure, said restrictive flow conduit providing substantially more restriction to fluid flow than said pilot conduit, whereby when said pilot opening is covered by said land, and while said ram is moving in a direction such that said pilot opening will become exposed to said given pressure, the resulting leakage through said pilot opening and through the finite clearance between said land and said surface is compensated by a corresponding flow through said restrictive flow conduit to prevent premature switching, but when said opening becomes exposed fully to said region of given pressure, the resulting greater flow through said pilot conduit operates to switch the valve.

In a hydraulically driven hammer system, a hydraulic piston and cylinder assembly and means for actuating said assembly for causing reciprocal relative movement between the piston and cylinder thereof, a massive ram connected to a moveable part of said piston and cylinder assembly, said massive ram being guided by a frame for reciprocal relative movement therein, a switching valve for sequentially connecting a chamber in said piston and cylinder assembly to sources of higher and lower pressure to reciprocally move said ram in hammering and retraction directions, respectively, said valve comprising a housing formed with a internal bore, first and second inputs from said source of higher and lower pressure respectively and opening into said internal bore at spaced apart locations, an output connected to said piston and cylinder assembly chamber and opening into said internal bore at a location between said first and second inputs, a first valve spool element moveable reciprocally in said bore for covering and uncovering said first input, a second valve spool element also moveable reciprocally in said bore for covering and uncovering said second input, an abutment spacer in said bore for maintaining said spool elements sufficiently far apart so as not to allow said spool elements to cover said output, said abutment spacer being of sufficient length to communicate movement of said second valve spool element, beyond its input closing position, to said first valve spool element to move same to an input opening position, said first spool element being biased on an input closing position and means for actuating said second valve spool element to move back and forth in said bore in response to predetermined movements of said ram.