Abstract: An apparatus has a pilot-operated spool valve connecting first and second work passages selectively to a supply conduit and a tank conduit. A first check valve normally allows fluid flow only in one direction from the first work passage to a first workport and when pilot-operated allows bidirectional fluid flow. A second check valve normally allows fluid flow only from the second work passage to a second workport and when pilot-operated allows bidirectional fluid flow. A first pilot valve selectively applies pressure to one end of the spool and to pilot operate the first check valve. A second pilot valve selectively applies pressure to another end of the spool and to pilot operate the second check valve. When fluid drains from a workport to the tank conduit, the associated check valve operates to maintain a predefined pressure in the first or second work passage through which that fluid flows.

Abstract: An apparatus has a pilot-operated spool valve connecting first and second work passages selectively to a supply conduit and a tank conduit. A first check valve normally allows fluid flow only in one direction from the first work passage to a first workport and when pilot-operated allows bidirectional fluid flow. A second check valve normally allows fluid flow only from the second work passage to a second workport and when pilot-operated allows bidirectional fluid flow. A first pilot valve selectively applies pressure to one end of the spool and to pilot operate the first check valve. A second pilot valve selectively applies pressure to another end of the spool and to pilot operate the second check valve. When fluid drains from a workport to the tank conduit, the associated check valve operates to maintain a predefined pressure in the first or second work passage through which that fluid flows.

Abstract: A system for operating a single acting hydraulic cylinder includes a directional valve that has one extreme position in which a workport is connected to a tank return conduit, another extreme position where the workport is connected to a pump supply conduit, and a closed intermediate a position where the workport is disconnected from both the pump and the tank. The directional valve is pilot operated and is biased toward the one extreme position by a spring. An electrically operated primary applies pilot pressure to the directional valve alternately from the pump supply conduit and the tank return conduit. A pilot operated check valve has a first state which restricts fluid flow only from the workport toward the chamber and a second state in which fluid can flows from the chamber to the workport. The system has a pressure compensation that also provides self priming of the directional valve.

Abstract: A system for operating a single acting hydraulic cylinder includes a directional valve that has one extreme position in which a workport is connected to a tank return conduit, another extreme position where the workport is connected to a pump supply conduit, and a closed intermediate a position where the workport is disconnected from both the pump and the tank. The directional valve is pilot operated and is biased toward the one extreme position by a spring. An electrically operated primary applies pilot pressure to the directional valve alternately from the pump supply conduit and the tank return conduit. A pilot operated check valve has a first state which restricts fluid flow only from the workport toward the chamber and a second state in which fluid can flows from the chamber to the workport. The system has a pressure compensation that also provides self priming of the directional valve.