A spool valve actuator may include a stop fixed to the case with a cylindrical body member having a first set of slots of a first length at regular circumferential distances and a second set of slots of a second length at regular circumferential distances offset from the first set of slots, both set of slots configured to slidably receive a proximal portion of a positioner, a ratchet member may comprise, a cylindrical body slidably attached to the spool valve shaft and keyed to the stop to prevent relative rotation, a distal edge comprising a plurality of distally facing teeth configured to engage the proximal portion of the positioner when the ratchet is moved away from the stop, the positioner may comprise a plurality of proximally extending positioning members configured to engage with both the distally facing teeth and the slots in the stop.