The pump circulates fluid in a closed circuit, as part of a test system. The fluid discharge is routed back to the inlet via a pressure reducing system.

The actuator of the pump consists of a flywheel driven by a constant velocity electric drive. A fibre rope connects the pump rod end to a boss on the flywheel, via a deflection sheave. The idea is that this arrangement reciprocates the pump with a sinusoidal velocity profile. Note the actuator can only pull on the rod, it cannot push it to get the piston to return (rope only works in tension). To do this, we use hydraulic means (i.e. we configure the pump's inlet pressure to be sufficient to force the piston to return). The rope remains in tension on both the extension and retraction of the pump, but is much higher on the extension as this is the pump discharge stroke (pulling against high pressure). The actuator essentially brakes the return of the piston during the inlet stroke.