In Fig. 1 it will be noted that the exploded gases are expelled by the rising piston from the cylinder through the exhaust valve e and exhaust pipe e p.

Fig. 5 (a) shows the exhaust valve in its position in the wall of the cylinder and closed against the escape of the exhaust gases.

Fig. 5 (b) shows a section of the valve when it is open, leaving a free escape for the exhaust gases in the direction of the arrow.

It will be noted that the valve is kept in its seat by means of a spring, and it remains in this position throughout the suction, compression and explosion strokes. During the exhaust stroke, however, when the explosive gases are expelled from