Abstract: A solenoid valve includes a housing including a channel, a single-acting through hole, a double-acting through hole, a spring biased spool in the channel, a lateral outlet communicating with the double-acting through hole, and a hole element passing through an edge of the channel to communicate with both the double-acting through hole and the channel; a switch on the housing and including an axial tunnel, a shaft in the tunnel, a lateral single-acting hole communicating with the tunnel, a double-acting hole communicating with the tunnel, and a linking hole perpendicular to the tunnel but not communicating therewith; a pilot valve on the switch; a base at a bottom of the housing, and a spring biased check valve at a lower opening of the housing and the base, the check valve communicating with the single-acting through hole.

Abstract: A guidance control system for trailing implements attached to a tractor is disclosed. The system can function to steer the implement in a row crop, for example, and can also steer the tractor. A proportional servo valve having a rotatable spool is disclosed, which valve can be controlled to operate in an open center or closed center modes of operation.

Abstract: A single tool carrier reciprocatingly driven in opposite directions by a pair of double ended reciprocating pneumatic pistons, one of the pistons driving the carrier through rack and pinion gear means and the other piston driving the carrier through a pin integrally connected to the carrier, mounted vertically on the carrier and engaging the said other piston. Seal rings, preferably of Teflon, are mounted on both ends of both pistons. The pistons operate in opposite directions. One piston is made relatively light so that its weight and the weight of the other shoe are counterbalanced against each other.

Abstract: The actuator includes two piston motors interconnected in opposed driving relation with a fixed axis rotary shaft, and fluid pressure control means for controlling the piston motors so that they rotate the shaft bi-directionally at constant rotational velocity with constant resultant torque. The two piston motors preferably are of different effective cross sectional areas, the smaller motor being continuously pressurized with fluid composed solely of fluid from a fluid pressure source, and the larger motor being selectively pressurized with fluid made up of fluid from the fluid pressure source together with fluid exhausted from the smaller motor. A single valve controls fluid flow to and from the piston motors to effect bi-directional shaft rotation, or maintain the shaft in a fixed position. The valve may be operated automatically by servo control means responsive to the positions of the piston motors.