why do they "have to"? the arm is a lever, which can multiply the travel beyond the pivot, the diaphragm can't move far [look at the depth of the pump body] and the actuator arm is basicly run by a cam lobe with little lift, maybe 1/4" ... and isn't the dual action pump working when moving both directions? that should mean it only has to move half as far for the same amount of work .... besides, I just checked an old regular pump - moves about 1/4", once the slack is out
Bill
