Title: Directional control valve system

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Abstract: A system particularly useful in trucks for manipulating a hydraulically operated work station comprising a network of four intercommunicating directional valves including a primary valve directing the flow to or from the work station and located between the work station, a hydraulic fluid pump and a fluid reservoir. The valve is designed so that when in the hold position fluid is continuously circulated from the reservoir through the pump and valve and movement of the work station is prohibited. The primary valve is normally biased to its hold position and is air actuated to its work or return position by an operational valve manipulated by a safety manual control. The operational valve directs air to the work or return side of the primary valve which is provided with free floating pistons for adjusting the primary valve spool in response to the flow of air in a surrounding chamber. The chambers and valve housing cooperate to fully seal the spool against contamination. Located in the air line on the work side between the primary and operational valve is a limit valve which senses the point of maximum desired travel of the work station and automatically returns the operational valve to its hold position as that point is reached. A safety valve is provided when desirable at the source of air pressure to protect the source if air pressure is lost in the system. When actuated by the loss of air pressure below a predetermined amount, the safety valve stops air flow to the operational valve which shifts the system automatically to neutral.


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