Fig. 281.
Fig. 282.
The auxiliary valve controls the admission and exhaust of steam for the steam chest and valve piston in the manner common to all slide valve engines. The valve piston is connected to the main valve, which allows the valve to find its own bearings on the seat and not only takes up the wear automatically, but produces even wear.
To set the auxiliary valve, see that the valve is in its central position when the rocker arm is plumb, and that the collars on the valve stem are located at equal distances from each end of the sleeve. When the piston moves to one end of the stroke, the auxiliary valve will open the small port at the opposite end, provided the collars on the valve stem have been properly placed. Setting the collars closer together shortens the stroke of the piston, and moving them farther apart lengthens the stroke. The piston should always make a full stroke without danger of striking the cylinder heads.
THE DEANE.
The details of the valve gear used on the Deane single cylinder steam pumps are shown in the accompanying engraving. The main valve is operated by a small piston called the valve piston, shown in [Fig. 286]. The ears on the main valve fit freely but without lost motion into a slot cut in the valve piston, so that when the valve piston moves in either direction it carries the main valve with it.
The valve piston is fitted to the valve chest and is operated by steam admitted alternately to the opposite ends of the chest. The movements of this valve piston are controlled by a secondary valve, which admits and exhausts the steam to the valve piston through the small ports at the sides of the steam chest. The secondary valve derives its motion from the valve stem, tappets, links and the piston rod as shown.
The valve piston is steam jacketed which insures equal expansion of the parts in starting the pump and prevents the seats from pinching the valve piston before these parts have acquired a uniform temperature.
The action of this pump is as follows: Suppose the piston moving in the direction of the arrow nears the end of the stroke; the tappet block comes in contact with the left-hand tappet and throws the secondary valve to the left until it’s edge, A, [Fig. 284], uncovers the small port, S, Fig. 283, admitting steam to the valve piston.