When shaft A rotates, motion is transmitted through worm 1, worm wheel 2 and connecting rod 3 to slider 4, piston rod 5 and piston 6. Space a between piston 6 and membrane 15 is filled with fluid. As piston 6 travels to the right a vacuum is set up in space a and membrane 15 is bent to the right. This sets up a vacuum in chamber d into which the fluid to be metered is drawn through valve 7. As piston 6 travels to the left, membrane 15 is bent to the left, forcing out the metered fluid through valve 8 into the discharge pipeline. The accuracy of pump delivery is maintained by the provision of special valve 9 which by-passes fluid into space a, replenishing leakage losses. Relief valve 10 protects the system against overloads by releasing fluid from space a. The amount of fluid fed in each stroke can be varied without stopping the pump as follows: as slider 4 travels to the left, a part of its stroke is idle until it reaches gear 11, mounted on the threaded portion of piston rod 5. In its travel to the right, a part of the stroke of slider 4 is also idle until its cover reaches nut 12 which is screwed on the end of piston rod 5. The amount of idle travel of the slider (and dwell of rod 5) depends upon the distance between gear 11 and nut 12 which can be adjusted by turning gear 13, meshing with gear 11. The position of gear 11 on rod 5 is registered by indicator 14 which shows the length of the piston stroke on a scale.
$4041$THP,FD$