A hydraulic control system that comprises a hydraulic pressure line, a hydraulic fluid control mechanism and a lag network coupling the pressure line to the control mechanism for restricting flow of hydraulic flow therethrough, and thereby delaying and damping response of the control mechanism to fluid pressure fluctuations at the hydraulic line. The lag network comprises check valve that includes a flow passages interconnecting the hydraulic line and the control mechanism, a valve element, and a spring resiliently urging the valve element to close the passage, such that resistance to fluid flow increases as fluid flow decreases between the hydraulic pressure line and the control mechanism. Preferably, a pair of such check valves are connected in parallel between the hydraulic pressure line and the control mechanism for controllably restricting fluid flow in both directions. To offset decreasing resistance as a function of increasing fluid flow through the check valve or valves, an orifice that exhibits increasing resistance as function of fluid flow may be connected in series with the valves.
A bidirectional check valve controls movement of fluid. A valve body has an opening, a further opening and a passage connecting the opening and the further opening. A poppet is disposed within the passage of the valve body, and a spring is coupled to the poppet. A further poppet is disposed within the passage formed in the first mentioned poppet, and a further spring is coupled to the poppet and to the further poppet. When fluid passing through the opening in the valve body exerts a force on the poppet that is greater than the spring force, the further portion of the outer surface of the poppet is directed away from the further portion of the wall of the passage and permits the fluid to flow from the opening in the valve body through a channel and to the further opening in the valve body. When fluid passing through the further opening in the valve body exerts a force on the further poppet that is greater than the further spring force, the further portion of the outer surface of the further poppet is directed away from the further opening in the valve body to open a further channel in the poppet and permit the fluid to flow from the further opening in the valve body through the further channel, at least one opening in the further poppet, a further passage in the further poppet, a further opening in the further poppet and an opening in the poppet to the opening of the valve body.
A hydraulic circuit is disclosed that can include a flow control element, a pressure compensator connected via a pair of load sense lines to an inlet line and an outlet line, respectively, of a flow control element to provide a constant pressure drop across the flow control element, and a load sense line control valve installed in a load sense line to provide controllable resistance in a flow passage in opposite flow directions, the resistance in each flow direction being different. The load sense line control valve can include a restrictive orifice followed by a spring-loaded check valve in a first flow direction and at least one other restrictive orifice and a check valve in a second flow direction, the second flow direction opposing the first flow direction.
