Lock valve for double acting cylinder

Abstract

A lock valve for a double acting cylinder including a housing that defines first and second fluid paths for supplying a control fluid to the cylinder to actuate pushing cylinder extension or pulling cylinder retraction and to positively locate the cylinder in any partially extended position. First and second spaced check valves are respectively disposed along the first and second fluid paths to normally prevent reverse fluid flow therealong from the cylinder. Aligned openings of the check valves are closed by spring biased valve elements thereof from the opposite side of each opening as the other check valve. A bore in the housing between the check valves slidably receives a control piston with first and second actuating portions for respectively moving the check valve elements upon piston movement in opposite directions to open the check valves and permit the reverse fluid flow from the cylinder. First and second sides of the control piston respectively surround the first and second actuating portions and are communicated with the first and second fluid paths as well as being biased by a pair of helical springs to provide a centering action of the control piston in a manner that prevents leakage from the cylinder. When control fluid is pumped through either fluid path, the associated check valve opens to permit fluid flow to the cylinder and the control piston is concomitantly moved against the action of the helical springs to open the other check valve and thereby permit reverse fluid flow from the cylinder. The helical springs encircle the actuating portions and have outer ends seated about the check valve openings as well as inner ends seated by a pair of stop members that respectively engage the first and second sides of the control piston. Stop surfaces on the housing are located at ends of the control piston bore and are spaced from each other the same distance as the length of the control piston so that each engages the control piston in its center position. The lock valve housing is preferably mounted on one end of a double acting cylinder opposite the cylinder end through which its piston connecting rod extends and is thereby particularly adaptable for use as a tilting cab control cylinder. A bore through the housing connects the first fluid path with the cylinder to provide its extension while a conduit connects the second fluid path with the cylinder to provide its retraction.