Experimental Studies of a Novel Alternating Flow (AF) Hydraulic Pump

The ideal variable displacement pump for a displacement control circuit is efficient across a wide operating range and readily mounted on a common shaft with multiple pumps. This paper presents a novel variable displacement pump architecture for displacement control circuits that uses the concept of alternating flow (AF) between piston pairs that share a common cylinder. The displacement is adjusted by varying the phase angle between the piston pairs. When the pistons are in phase, the pump displacement is at a maximum and when the pairs of pistons are out of phase, fluid is shuttled between the pistons and the pump produces no net flow. A prototype of the AF pump was constructed from two inline triplex pumps that were modified so that three piston pairs were created. The crankshafts of the two pumps were connected via a sprocket-and-chain transmission. The sprockets allow for accurate measurement of the phase angle, which is adjusted, in this early phase prototype, by disassembling the chain and shifting the sprockets. The prototype AF pump was then mounted to the test stand and experiments were conducted to map the AF pump efficiency and cylinder pressure dynamics across a range of operating pressure, speed, and displacement. The AF pump’s efficiency was measured for 8 diferent phase angles with an efficiency of near 90% at full flow and 65% at 36% displacement. The experimental results were compared to simulation results, presented in a companion paper at this conference.