After passing through pressure reducer 1 (see Fig. a) in which its pressure is reduced, the compressed air is divided into two streams. Part of the air passes into external chamber a of pneumatic relay 2; the rest passes through second pressure reducer 3 and is delivered to nozzle 4 and further, through nozzle 5, to internal chamber d of relay 2. Surface irregularities are traced by stylus 6 mounted on lever 7. The movements of stylus 6 are transmitted to plate 8 which interrupts air flow from nozzle 4 into nozzle 5 and relay 2. The fluctuations of pressure in relay 2 are sensed by membrane 9 which is linked by levers to pen 10. Upon a drop in pressure in internal chamber d of relay 2, membranes 11 and 12 are bent inward. At this, valve 13 shuts off air flow to external chamber a and valve 14 connects the chamber to the atmosphere. Membrane 9 bends inward, moving the pen to the right. Upon an increase in pressure in internal chamber d, pen 10 moves to the left. Stylus travel over the surface being tested is accomplished by weight 15 (see Fig. b); the speed of travel being varied by piston-type regulator 16 which has flow-control valve 17. The motion of the weight is transmitted to drum 22, which feeds the paper chart, and to stylus 6 through pinion 18 and rack 19, as well as two bellows, 20 and 21, filled with liquid.
$4077$EHP,M$