Control circuit for a cylinder allowing flow between an upper and a lower chamber

A hydraulic control circuit arrangement for a single-acting cylinder having a slidable piston element in a cylinder housing, a first cylinder chamber facing the piston element, a second cylinder chamber separated from the first chamber by the piston element, and a piston rod extending from the piston element to an outer end thereof through the second cylinder chamber, comprising:

• a hydraulic power source for supplying an operating oil for operating the single-acting cylinder;
• a hydraulic tank for receiving and storing the operating oil;
• a directional control valve arranged between the hydraulic power source and the single-acting cylinder for controlling a supply of the operating oil from the hydraulic power source to the single-acting cylinder, the directional control valve being shiftable from a neutral position thereof to one of a first position whereat the first cylinder chamber of the single-acting cylinder is connected to the hydraulic power source and a second position whereat the first chamber of the single-acting cylinder is connected to the hydraulic tank;
• a first conduit of the operating oil for providing a fluid connection between the first cylinder chamber of the single-acting cylinder and the directional control valve;
• a second conduit of the operating oil for providing a fluid connection between the second cylinder chamber of the single-acting cylinder and the hydraulic tank;
• a third conduit of the operating oil for providing a short-circuiting fluid connection between the first and second cylinder chambers of the single-acting cylinder;
• a first pilot-operated vale for controlling an evacuation of the operating oil from the second cylinder chamber of the single-acting cylinder through the second conduit in response to a change in a pressure in the first cylinder chamber of the single-acting cylinder with respect to a preset pressure when the directional control valve is shifted to and maintained at the first position thereof;
• a flow control valve arranged in the first conduit and having an inlet port thereof directly and fluidly connected to both the first cylinder chamber of the single-acting cylinder and the third conduit, and an outlet port thereof directly connected to the directional control valve, the flow control valve controlling a flow of the operating oil in the first conduit when the operating oil is allowed to flow out of the first cylinder chamber of the single-acting cylinder, to thereby generate a pressure differential thereacross;
• and
• a second pilot-operated valve arranged in the third conduit and urged to a first position thereof providing a short-circuit fluid connection between the first and second chambers of the single-acting cylinder through the third conduit when the directional control valve is shifted to the second position thereof, the second pilot-operated valve being connected to one port of said directional control valve, said one port being a port for supplying said operating oil to said first conduit when said directional control valve is shifted to said first position thereof, said second pilot-operated valve being shifted from the first position thereof to a second position thereof to allow only the operating oil to flow from the second to first cylinder chamber of the single-acting cylinder when the directional control valve is shifted to the first position.

A hydraulic control circuit arrangement for a single-acting cylinder having a slidable piston element in a cylinder housing, a firs cylinder chamber facing the piston element, a second cylinder chamber separated from the first chamber by the piston element, and a piston rod extending from the piston element to an outer end thereof through the second cylinder chamber, comprising:

• a hydraulic power source for supplying an operating oil for operating the single-acting cylinder;
• a hydraulic tank for receiving and storing the operating oil;
• a directional control valve arranged between the hydraulic power source and the single-acting cylinder for controlling a supply of the operating oil from the hydraulic power source to the single-acting cylinder, the directional control valve being shiftable from a neutral position thereof to one of a first position whereat the first cylinder chamber of the single-acting cylinder is connected to the hydraulic power source and a second position whereat the first chamber of the single-acting cylinder is connected to the hydraulic tank;
• a first conduit for the operating oil for providing a fluid connection between the first cylinder chamber of the single-acting cylinder and the directional control valve;
• a second conduit of the operating oil for providing a fluid connection between the second cylinder chamber of the single-acting cylinder and the hydraulic tank;
• a third conduit of the operating oil for providing a short-circuiting fluid connection between the first and second cylinder chambers of the single-acting cylinder;
• a first pilot-operated valve for controlling an evacuation of the operating oil from the second cylinder chamber of the single-acting cylinder through second conduit in response to a chane in a pressure in the fist cylinder chamber of the single-acting cylinder with respect to a preset pressure when the directional control valve is shifted to and maintained at the first position thereof;
• a flow control valve arranged in the first conduit and having an inlet port thereof directly and fluidly connected to both the first cylinder chamber of the single-acting cylinder and the third conduit, and an outlet port thereof directly connected to the directional control valve, the flow control valve controlling a flow of the operating oil in the first conduit when the operating oil is allowed to flow out of the first cylinder chamber of the single-acting cylinder, to thereby generate a pressure differential thereacross;
• and
• a second pilot-operated valve arranged in the third conduit and urged to a first position thereof providing a short-circuit fluid connection between the first and second chambers of the single-acting cylinder through the third conduit when the directional control valve is shifted to the second position thereof, the second pilot-operated valve being shifted from the first position thereof to a second position thereof to allow only the operating oil to flow from the second to first cylinder chamber of the single-acting cylinder, when the directional control valve is shifted to the first position, said flow control valve and said first and second pilot-operated valves being integrally assembled into a single valve unit independent from said directional control valve, and said first and second pilot-operated valves being provided with respective pilot lines connected to pilot pressure obtaining ports formed in said directional control valve.