Each cylinder has two actively controlled poppet valves, one to each of the high and low pressure manifolds. When idling (left in the diagram below) the fluid flows in and out around the low pressure valve. The high pressure valve remains closed and isolates the reciprocating cylinder from the high pressure fluid. When pumping (right), the microprocessor closes the low pressure valve to send fluid to the high pressure service.

It is also possible to hold the high pressure valve open, taking fluid from the high pressure output.

The net result of the rapid sequenced valve actuation is that, at the end of each stroke, each cylinder can be reconfigured to either pump, motor or idle. By controlling the sequence of cylinder enablings, the machine can pump fluid to a hydraulic service or accept it back (while the returning fluid actually helps to drive the crankshaft of the machine) at infinitely variable flow-rates. The valve actuation decisions are occurring every four or five milliseconds in a typical multi-cylinder pump driven at industrial diesel speeds, which gives an effective frequency response greater than 20 Hz.

Further information about the benefits of Digital Displacement® can be found on the Advantages pages, and in the Applications pages.