The steam acts to throw the main valve only near the ends of the valve travel, and being already in motion the valve requires but very slight help to complete its stroke quickly without shock. The motion of the auxiliary valve is synonymous with the main piston so there can be no practical dead center. The valves are very durable under such easy motion. _With this arrangement of valves no setting is necessary_ because when assembling the parts the centers of the pendulum lever and the toes on the rocker shaft are adjusted parallel with one another. THE McGOWAN. The McGowan single cylinder steam pump and section is shown in Fig. 275. Its main valve is of the ^B^ form and is driven by a valve piston. Steam enters the central port in valve seat and into the cylinder through one of the cavities in the valve and exhausts through the opposite. The two tappet valves cover the auxiliary ports, shown by dotted lines, leading to the ends of the steam chest and connect with the main exhaust ports. These tappet valves are raised by means of levers, the ends of which project downward and into the cylinder so that when the piston nears the end of a stroke it comes in contact with the lever and raises it sufficiently to lift the tappet valves. Each tappet valve lever is pivoted on a pin which fits into a recess near the main ports, as indicated by the dotted lines. [Illustration: FIG. 275.] When the piston reaches the end of its stroke it lifts one of the tappet levers and with it the corresponding valve is raised from its seat, opening the port leading from the end of the steam chest to the main exhaust port. The pressure is thus relieved on one end of the valve piston and the steam pressing on the opposite end forces the valve piston to the opposite end of its stroke, thus reversing the distribution of steam to the cylinder and starting the piston on its return stroke. The valve piston thus moves back and forth, the ends of the steam chest being filled with steam at initial pressure. Steam escaping from one end of the steam chest causes a difference of pressure on the two ends of the valve piston, from which we realize the power to move the main valve. The tappet valves, having a very slight lift, operate without shock or noise. The main valve is connected with the valve piston so that all lost motion is taken up automatically. A rocker shaft, extending through the steam chest carries a toe moving in a slot in the top of the valve piston, so that the valve can be moved by hand. _To set the valves of this pump._ Simply keep the valves in order. The motion of the piston as it nears the end of the stroke opens and closes the valves. THE KNOWLES.