64 will have approximately seven turns more specifically the groove may have 1 2 turns in the area occupied by piston spring 78 and 5 6 turns in the remainder of the piston 62 it will be appreciated that a tight spiral path i e many turns makes it more certain that the rinsing agent will reach deposits in the annulus however too many turns could result in back leakage during the pumping stroke due to the corresponding reduction in the piston 39 s regions of higher diameter which are responsible for the piston 39 s tight fit within the piston channel it is to be noted however that since the forward stroke is very fast e g 1 5 milliseconds and the refill time is much longer e g 100 150 times longer the back leakage is dramatically smaller than the forward flow furthermore a helical groove of the type shown in fig5 causes fluid flow to transition from laminar to turbulent thereby restricting fluid flow thus the groove generally provides a flow path when the actuator is moving relatively slowly retracting and provides a sealing action when the actuator is moving fast pumping while the groove in the outer surface of the actuator piston is shown in fig9 as having a hemispherical cross section it is known that sharp edges in the flow path such as edges 134 in fig9 may cause further denaturing of the protein therapy drug therefore in a particular embodiment shown in fig1 groove 64 has a cross sectional shape including rounded edges 136 it should be clear however that.