23,017. Gibbs, A. Nov. 18. Regulators.-Relates to apparatus for compressing air into the frame &c. of a vehicle when running down hill, and utilizing it as an auxiliary driving power. The invention is described as applied to a bicycle. In order to maintain a constant pressure, a regulator of the form shown in Fig. 12 is used. An expansible corrugated metal case 34 is arranged between the air tube 32 and the reservoir. One side of the case carries an adjustable screwed stem 35, which bears on a valve spindle 36 so as to open the valve when the box collapses owing to the fall of pressure in the cylinder.