Closed center hydraulic valve control system for aerial lift

An aerial lift comprising:

• a base,
• an elongated boom supported by said base and including a free end,
• a fluid motor operably connected to said elongated boom,
• means for supplying hydraulic fluid to said fluid motor, said means for supplying hydraulic fluid including
• a hydraulic fluid pump operably connected to said fluid motor, and
• means for controlling the supply of hydraulic fluid from said hydraulic fluid pump to said fluid motor, said means for controlling including
• a pilot operated control valve having a first pilot fluid port and a second pilot fluid port,
• means for supplying pilot hydraulic fluid pressure to said first pilot fluid port and to said second pilot fluid port of said pilot operated control valve to control operation of said pilot operated control valve, said means for supplying pilot hydraulic fluid pressure including a first hydraulic fluid conduit operably connecting said hydraulic fluid pump to said first pilot fluid port of said control valve, and a second hydraulic fluid conduit operably connecting said hydraulic fluid pump to said second pilot fluid port of said control valve, and
• means for selectively venting hydraulic fluid from said first fluid conduit and said second fluid conduit, said means for selectively venting hydraulic fluid from said first fluid conduit including a first valve seat and a first valve member selectively engageable with said first valve seat and movable toward and away from said first valve seat, at least one of said first valve member and said first valve seat including notch means defining a first fluid port when said first valve member engages said first valve seat and said first valve seat and first valve member providing for increased fluid flow from said first fluid conduit when said first valve member moves away from said first valve seat, and said means for selectively venting hydraulic fluid from said second fluid conduit includes a second valve seat and a valve member selectively engageable with said second valve seat and moveable away from said second valve seat, at least one of said said second valve member and said second valve seat including notch means defining a fluid port when said second valve member engages said second valve seat and said second valve member and said second valve seat providing for increased fluid flow from said second fluid conduit when said second valve member moves away from said second valve seat.