Hydraulic circuitry for an excavator

A hydraulic system for a hydraulic excavator having drive motor means, a platform slew motor, a boom control motor, a jib control motor, and a bucket control motor, the improvement comprising:

• a pair of substantially identical variable capacity pumps for supplying fluid to said system;
• a first series of series connected distributors operative to selectively direct fluid from one of said pumps to the drive motor means and, the jib control motor;
• and,
• a second series of series connected distributors for directing fluid from the other of said pumps to the drive motor means, then the bucket motor and finally the boom control motor;
• and,
• combining means including a cross-over spool valve operative to make the fluid supplied to one series of said distributors available to the last distributor in said other series when said one series is in substantially the neutral position.

A hydraulic system comprising:

• first and second pumps, each having a pressure side and an intake side;
• conduit means defining first and second circulating paths for the first and second pumps respectively, and including respective ducts connected to the pressure side and intake side of each pump;
• a first control valve operatively associated with said first path and a first hydraulically operable load;
• a second control valve;
• a branch conduit interconnecting said second control valve and said second circulating path;
• a first check valve positioned in said branch conduit for allowing flow from the second circulating path to the second control valve, but blocking flow from said second control valve to said second circulating path;
• the second control valve connecting the second path with a respective hydraulically operable load through the branch conduit;
• a selectively shiftable auxiliary valve in said first path permitting circulation of a hydraulic medium therealong but actuatable to block said circulation, said auxiliary valve having a first position communicating between said duct connected to said pressure side and said duct connected to the intake side of the first pump and permitting return flow of fluid from the first path to the first pump and a second position blocking return flow of fluid;
• a shunt conduit connecting said first path, between said auxiliary valve and said first pump at the duct connected to the pressure side of the first pump, with said branch conduit at a point in said branch conduit between the first check valve and the second control valve;
• and
• a second check valve in said shunt conduit automatically opening upon shifting of said auxiliary valve into said second position for unidirectional flow of the medium between said first path and said branch conduit upon blockage of circulation in said first path by said auxiliary valve, whereby a load energized through the second control valve may draw upon medium through the branch conduit from both the first path and the second path.