All About Engines

290 All About Engines up and down by the nuts on the pump rod shown in Fig. 161. Now examine Figs. 165, 166, and 167. The first named shows the auxiliary valve ; the dotted lines indi- cate a recess on the face which moves over the main valve. The second and third figures show the front and back faces of the main valve. The lettering on the different views corresponds throughout. Suppose the piston to be at the end of the down- ward stroke. Then the main valve is in the right- hand position, as shown in Fig. 163, and the port c leading to the bottom of the cylinder is open to steam. This is clearer from Fig. 164. The piston now rises, and the auxiliary valve begins to move in the same direction when the piston has half completed its stroke, By the time the piston has completed three-quarters of its stroke the port c is closed by the auxiliary valve (see Fig. 164), and the remainder of the stroke is completed by the expansion of the steam in the cylinder. The upward movement of the auxiliary valve, which results in the port c being closed, also opens to exhaust the port E, leading to the left-hand end of