Hydraulic control circuit for pile driver

A pile driver arrangement including:

• a) a reciprocal impact member having a lower contact end and an upper end and contact means on said impact member for operating a trip valve,
• b) a hydraulic cylinder having a lower rod end and an upper blind end located above said impact member upper end,
• c) a reciprocal piston axially movable in said hydraulic cylinder,
• d) a piston rod connecting said impact member upper end to said reciprocal piston, whereby upward movement of said reciprocal piston in said hydraulic cylinder lifts said impact member,
• e) a first hydraulic fluid conduit means connecting said upper blind end of said hydraulic cylinder and said lower rod end of said hydraulic cylinder,
• f) a hydraulic fluid storage tank,
• g) a pump for supplying hydraulic fluid under pressure from said storage tank to said lower rod end of said hydraulic cylinder to move said piston upwardly in said hydraulic cylinder and thereby lift said impact member,
• h) a second hydraulic fluid conduit means connecting said pump and said lower rod end of said hydraulic cylinder,
• i) a control valve located in said second conduit means for controlling the flow of pressurized hydraulic fluid through said second conduit means from said pump to said lower rod end of said hydraulic cylinder, a longitudinally spring loaded spool in said control valve and an orifice in said spool to permit a constant leakage of hydraulic fluid through said control valve to said tank,
• j) a third hydraulic fluid conduit means adapted to connect said pump to an adjustable trip valve,
• k) an adjustable trip valve connected to said third conduit means for shifting the longitudinal position of said spring loaded spool in said control valve to control the flow of hydraulic fluid from said pump to said lower rod end of said hydraulic cylinder and an adjustable control member in said trip valve,
• l) a fourth hydraulic fluid conduit means connecting said trip valve and said control valve whereby movement of said adjustable control member in said trip valve by said contact means on said impact member shifts the position of said spring loaded spool in said control valve,
• m) a replenishment check valve in said first conduit means, whereby hydraulic fluid can only flow in said first conduit means from said upper blind end of said hydraulic cylinder to said lower end of said hydraulic cylinder to fill said lower blind end of said hydraulic cylinder when said piston is decelerating upward after said adjustable control member in said trip valve is adjusted to permit hydraulic pressure in said fourth conduit means to shift the longitudinal position of said spring loaded spool in said control valve,
• n) additional hydraulic fluid conduit means connecting said upper blind end of said hydraulic cylinder and said tank,
• o) a fifth hydraulic fluid conduit means connecting said lower rod end of said hydraulic cylinder and said upper blind end of said hydraulic cylinder,
• p) a drop valve located in said fifth conduit means, said drop valve having first and second ports connected to said fifth hydraulic fluid conduit means and a third port connected to a sixth hydraulic fluid conduit means,
• q) said sixth hydraulic fluid conduit means connecting said third port of said drop valve to said control valve, whereby a pilot pressure is supplied from said control valve to said third port of said drop valve, and
• r) said drop valve including a poppet in communication with said third port and biasing means for holding said poppet in the closed position in combination with the pilot pressure from said control valve during the upward movement of said impact member, whereby during the drop portion of the operating cycle of said impact member when said control valve is in the shifted position, hydraulic fluid flow in said fifth conduit means is sufficient to open said poppet of said drop valve and flow into said upper blind end of said hydraulic cylinder, said control valve being held in the shifted position by differential hydraulic pressure as generated by said biasing means on said drop valve poppet in said fifth conduit means.