Historical and Socio-cultural Origins of Amazonian Dark Earth

A continuously variable speed converter is incorporated in a main housing of a fluid pump and is drivingly connected at an output shaft thereof to a pump rotor so as to transmit the driving power of an engine to the pump rotor at various output/input speed ratios. An actuator is operatively connected at its piston to a speed change mechanism of the speed converter and is responsive to pressurized fluids, which are delivered from the pump, respectively, through and not through a throttle element provided on an outlet passage of the pump. The piston is biased by means of a spring to operate the speed change mechanism to maintain constant the pressure difference between fluids before and behind the throttle element, so that fluid may be delivered from the pump approximately at a predetermined flow rate regardless of changes in engine rotational speed.