Pumps 1, 2 and 3 are connected to the tank through pipe 14 with check valve 15 which prevents fluid return to the tank. Pump 4 is connected to the tank through pipe 16. This arrangement provides for operation in series so that pump 4 delivers fluid through open valve 8 into pipe 14, valve 15 closes and pumps 1, 2 and 3, supplied by fluid under pressure, deliver it into pipeline 13 at double pressure. All four pumps are connected to delivery pipeline 13 through check valves 9, 10, 11 and 12, which prevent fluid in the delivery pipeline from returning to the pumps. Fluid delivery is varied by turning on valves 5, 6, 7 and 8 in various combinations. The system can provide 15 different steps of travel of the operating mechanisms connected to pipeline 13.
$4171$CHP,Dr$