392 AIR GAUGES 



Tube A is connected to one end of the lever kj by means 

 of the link c. This lever is pivoted at e, and the end j forms 

 a toothed sector that meshes with a pinion on the spindle /. 

 The spindle / carries the black hand, or pointer, of the gauge, 

 is hollow, and rotates about the spindle i, which carries the 

 red hand. Tube B is connected by link b to the lever fg at a 

 point below the fulcrum, or pivot, so that the red hand will be 

 turned in the same direction as the black one. The lower end 

 of the lever fg takes the form of a toothed sector that meshes 

 with a pinion on the spindle I and operates the black hand. 



Copper pipe should be used for air-gauge connections in 

 preference to iron pipe, because the latter, if not carefully and 

 correctly adjusted, will put a strain to the mechanism of the 

 gauge when coupled to it, that will affect the accuracy of the 

 indications; also, the gauge will indicate incorrectly if situated 

 in too high a temperature. 



Operation of Gauge. As brake-pipe pressure connects with 

 M, air under pressure enters tube A and tends to straighten it 

 out. This causes the free end of A to move to the left, drawing 

 the link c with it, thus moving the toothed sector j to the right. 

 As this sector engages with the spindle /, the latter is made to 

 move clockwise, that is, to have a motion in the same direction 

 as the hands of a clock. The black hand is thus given a similar 

 motion. 



Main-reservoir pressure acts within the tube B to straighten 

 it, and the free end is moved to the right. As the bar b is 

 connected below the fulcrum of the lever fg, the movement 

 of the free end of B will cause the toothed sector g to move 

 to the right and turn the red hand clockwise also. The 

 greater the pressure within the tubes, the greater will be the 

 tendency for them to straighten out, and the higher will be 

 the pressure registered by the gauge; d and h are small coil 

 springs to take up the play or backlash in the teeth of the 

 sector and pinion. 



