[55]. Centrifugal brake, or clutch. The weight segments are driven into contact with the ring by centrifugal force. Springs may be used to return them out of action.
[56]. Three-segment compound brake: grips the wheel all round.
[57]. Compound bar brake, with right and left hand screw grip levers, used for heavy gun compressors.
[58]. Compound ring brake, on similar principle to [No. 57]. See remarks to [No. 41].
[59]. Wedge and split ring, used for internal brake ring or clutch, in a similar way to [No. 38].
[60]. Hollow drums, with radial pockets, half filled with loose material, or water, mercury, &c., which retard the motion of the drum by the weight and friction of the loose material.
An hydraulic cylinder and piston is frequently used as a brake or retarding device for reciprocating motion, the water passing from one side of the piston to the other, through an adjustable valve. Friction brakes are employed as dynamometers to indicate the power given off or absorbed by any piece of machinery. Automatic brakes (see [Sections 15] and [69]) are used for hoisting machinery, &c.
Brushes, formed of stiff bristles or wire, are used as a retarding device for circular or rectilinear motion.