NERVOUS DISCHARGES 



23 



fTl 



held down on ratchet 10 by the pawl spring 9 so as to engage 

 it. Valve 6 slides over the lag valve 12 and the ratchet valve 11. 



The ratchet valve 11 is shown in the figure in its original 

 position or right hand end of its stroke. When valve 6 is per- 

 mitted to make its return or outward stroke the valve 1 1 moves 

 also, pushed by the pawl 8. If valve 6 has a stroke of one and 

 one-half inches, valve 11 will move with it about one-fourth 

 inch. The lag valve 12 will also move the same „ 



distance pushed by valve 1 1 . When one -fourth 

 inch of the return stroke has been made, pawl 

 8 is tripped by the striking of the lug on top 

 of the pawl against a shoulder in casing 1. 

 When the ratchet valve is thus released, it 

 moves to the right, driven by lever spring 20 

 acting through finger lever 18, finger shaft 17 

 and rocking finger 16. When ratchet valve 11 

 moves to left it acts through the said finger 

 lever, etc., together with connecting rod 23 so 

 as to draw out dash pot plunger 24 and thus 

 suck air (or water) through check valve 27. 

 When, on the other hand the ratchet valve 

 moves to the right, the dash pot plunger is 

 driven back by the action of lever spring 20. 

 The air now contained in dash pot 25 is pre- 

 vented from escaping by check valve 27 and 

 can only pass out through adjusting cock 26. 

 In this way the return stroke of ratchet valve 

 is retarded and is very slow. When ratchet 

 valve moves to right on its return stroke it 

 leaves the lag valve 12 behind. 



If the time interval before a second stroke 

 of spur valve 6 is long enough, ratchet valve 

 1 1 will have reached its original position and its 

 second stroke will be the same as the first and 

 lag valve 12 will not be moved. If on the other hand, the time 

 interval is short so that the second stroke of the spur valve 

 comes before the ratchet valve has arrived at its original posi- 

 tion, the ratchet will cause the ratchet valve to advance further 

 to the left than before and hence the lag valve will be advanced 

 further to the left. 



27 



Figure 2. 

 mitter. 



Trans- 

 Trans- 



verse section on 

 line A A of Fig- 

 ure 1. 



