Control valve system with float valve

A hydraulic control system for controlling an actuator having a pair of actuator ports, the system having a pump, a reservoir, a pilot operated main control valve for controlling fluid communication between the actuator, the pump and the reservoir, the main control valve having a pair of work ports communicated with the actuator ports, first and second pilot valves for controlling operation of the main control valve, one of the pilot valves being operable to move the main control valve from a neutral position holding the actuator stationary to a first position causing the actuator to move in a first direction, and the other pilot valve being operable to move the main control valve from the neutral position to a second position causing the actuator to move in a second direction, characterized by:

• a lockout valve comprising a pressure responsive poppet valve member movable in response to fluid pressure in a lockout chamber to control communication between a work port of the main control valve and a corresponding one of the actuator ports, a first lockout port communicated with a corresponding one of the main valve work ports, a second lockout port communicated with a corresponding one actuator ports, an orifice communicating the second lockout port with the lockout chamber;
• a vent passage communicating the lockout chamber with the main control valve;
• a vent check valve for controlling fluid flow through the vent passage;
• resilient means for urging the vent check valve to a closed position thereby preventing fluid flow out of the backout chamber via the vent passage;
• and
• pressure responsive means communicated with one of the first and second pilot valves for opening the vent check valve when the one pilot valve is pressurized.