The supplemental valve ports are shown in section 4.
To set the valve of this pump: Remove the steam chest, place the piston at mid stroke with the lever, plumb, then set the stem at its mid position with the secondary valve in place. See that the tappets measure equal distances either side of the tappet block.
Note.—These small ports are not liable to fill with oil and dirt in practice, on account of their direct connections. If through leakage or any other reason the valve piston should fail to throw the main slide valve, the projection B (see 1) on the valve stem (of which it is a part) compels the valves to move mechanically. So when steam is turned on, this pump is certain to begin its work.
Fig. 351.
The water end of this pump consists of a cylinder with valve chambers as shown. The piston rod has two stuffing-boxes, which makes a water seal around the rod so that no air can enter the cylinder, as the chamber between the two stuffing-boxes is kept constantly filled with water. It will be noticed that the suction pipe enters the pump in such a position in relation to the valves that both suction and discharge valves are perpetually immersed in water.
When this pump is pumping air only, there is sufficient water left within the valve chambers to provide a water seal under all working conditions. The valves in this pump are easily reached for inspection or repairs, a hand-hole being provided for each valve, with proper covers, which are easily and quickly replaced.
The Worthington Vertical Beam Vacuum Pump with condenser attached is shown in Fig. [351].
This is a pump of great simplicity and strength. The figure shows a compound engine for using high pressure steam; these machines can be built with simple steam cylinders of equal diameters, but they are not recommended except in special cases; for example where the steam pressure is very low. Each side of the pump end is single-acting, the buckets being of the form used for years in detached air pumps in marine service. The two sides are connected together by a beam and links attached to the cross-heads. As one side comes down and does little work, the other side makes an up-stroke and does full duty in emptying the condenser to which the suction is attached.