the left will open the first orifice 70 to the second pressure chamber 54 a drain valve 64 is disposed within the passageway 62 having an open and a closed position a mechanical device such as a spring 72 biases drain valve 64 toward the open position and an electrical device such as a solenoid 74 biases the drain valve 64 toward the closed position when drain valve 64 is in the open position fluid is capable of passing through passageway 62 to tank 40 when drain valve 64 is in the closed position fluid is restricted from flowing through passageway 62 to tank 40 and from flowing to either of the first or second orifices 68 70 from the other of the first or second orifices 68 70 during normal operation of the primary pump 22 solenoid 74 is energized moving drain valve 64 to the closed position in this manner pressurized fluid may be provided to and from the first and second chambers 54 56 to move actuator 50 and change the angle of the swashplate and thus the displacement of the primary pump 22 upon loss of electrical power the control hardware 30 may assume the configuration illustrated in fig4 in this condition the first and second control valves 58 60 are actuated by their respective springs to a flow passing position.