The accompanying engravings illustrate the cylinder valves and valve motion of the Burnham single cylinder pump. Fig. 294 is a plan of the main cylinder valve face, having the same arrangement of ports as the cylinder shown in Fig. 293. A longitudinal section of the steam cylinder is shown in Fig. 292. Motion is imparted to the slotted arm and cam, A, by means of a crosshead and a roller on the piston rod. The cam works between and in contact with two blocks on the valve stem, and by adjusting these two blocks the stroke may be shortened or lengthened, as the case may require. The valve stem of the auxiliary valve, H, Fig. 293, always moves in a direction opposite to that of the piston. The action of this valve alternately admits steam through the double ports, J J, and K K, to each end of the valve cylinder, causing the valve piston, I, to move the main slide valve, D, which, in turn, admits steam to the main cylinder through the double ports, E E, and L L. As the travel of the cam is only one-fifth that of the piston travel, the valve moves slowly, and without jar or noise which is often caused by long travel and rapid motion. [Illustration: FIG. 293.] [Illustration: FIG. 294.] Steam enters the steam chest at B, and fills the space, F, between the valve piston heads and the auxiliary valve chest, G, shown in Fig. 292. With the auxiliary valve, H, in the position shown, Fig. 293, steam passes into both ports, J and K, but as the port, J_{1}, is closed by the valve piston, I, no steam can enter the valve cylinder through it, but the other port, K (extending to the extreme end of the valve cylinder), never being covered by the piston, is open, and admits steam into the space, M. As this port is quite small the space fills slowly and the piston moves gradually until it uncovers the last port, J_{1}, when the full volume of steam is admitted, which quickly moves the piston to the opposite end of the valve cylinder. During this movement of the valve piston, the large port, J, remains open to the exhaust until it is covered by the valve piston. When the port, J, is covered by the valve as at J_{1}, it has no connection with the exhaust, consequently, there being no outlet for the exhaust vapor, it is compressed and forms a cushion for the valve piston, I. The valve piston carries with it the main valve, D, which admits steam to the main steam cylinder through the double ports, E, E_{1}, and L, L_{1}, Fig. 294. The same cushioning and slow starting of the piston occurs in the main as in the valve cylinder, each having double ports. This arrangement insures a uniform travel of piston under varying degrees of load. A momentary pause of the piston at each end of the stroke permits the water valves to seat quietly, without shock or jar, and the slow initial movement of the piston (whereby the water columns are started gradually) relieves the pump and piping of excessive strains.