Abstract: A hydraulic drive circuit for tracked vehicles is provided in the form of two hydrostatic transmissions, one for each track with a control system for one track acting as a master control and the other transmission control following as a slave unit, except as modified by the signal from a manual steering control.

Abstract: A proportional pressure compensating hydraulic control valve having a valve body and a valve spool mounted in the valve body for movement from a neutral or open center position wherein fluid flows through the valve body to an operating position wherein the flow of fluid through the valve is restricted to direct inlet fluid through a flow control orifice to a pressure passage within the valve body, the pressure passage being connected to one of a pair of cylinder passages, the other cylinder passage being connected to a tank passage. The valve spool in an open center mode controlling the flow of fluid to the control orifice and being pressure compensated to maintain a predetermined flow rate through the control orifice, pressure compensation being achieved by imposing inlet and pressure passage pressures selectively to each end of the valve spool so that the valve spool responds to the pressure differential across the control orifice.

Abstract: A pilot operated check valve having pressure actuated poppet valves positioned to limit flow in one direction through each of two flow paths through the valve, each poppet valve including a one-way check valve to control reverse flow through the two flow paths and a spool positioned in said valve and being responsive to inlet pressure in one or the other of the flow paths to open the check valve in the opposite fluid flow path when the pressure differential between inlet pressure and return pressure is within a predetermined ratio.