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.
The condensing chamber is usually placed at the rear and connects directly with the channel plate at the bottom of the pump. The opening shown in front is for the discharge water.
The steam cylinders are so arranged that either piston may be examined by removing its cylinder head, without disturbing the other cylinders. The valves are of the Corliss, or semi-rotative, type and the high-pressure cylinders are provided with cut-off valves to assure the desired ratio of expansion.
The interior of each air cylinder may be inspected by removing the plates shown in front, near the middle. There are also two plates at the top for inspection of the discharge valves. The four machinery steel columns form a light but very strong frame allowing free access to the working parts.
The next four cuts show Dean Brothers’ twin cylinder air pumps with their special steam valve gear. They are made for and supplied with either surface or jet condensers. See Fig. 352.
The arrangement of the valve gear is such that steam will be applied at the upper end of one piston at the same instant that it begins to act on the lower end of the other. By this device steam is so controlled in the steam chests that no pressure comes on the main pistons, until the moment that both are ready to move, after having reached the full limit of their stroke, thereby securing an exactly uniform, but opposite, motion of the pistons. Fig. 354 is a sectional elevation of the steam cylinder and steam chest; Fig. 353, a front elevation; Fig. 355, a section of the air cylinder, and Fig. 352, an exterior perspective view of the pump.