The piston rods are separable at the crossheads. The crossheads are of steel. The steam cylinders and pump cylinders are connected by six heavy steel stretcher rods. Adjusting valves are fitted to steam cylinders for controlling motion of pistons. The valve gear is provided with a special lever adjustment by which the length of stroke of pistons may at any time be changed, even while the pump is running.
In Fig. [356] is shown a form of independent vacuum pump, with its condenser, built by the Conover Mfg. Co.
This apparatus consists of a jet condenser with air pump, boiler feed pump, and engine to drive both, combined as one machine. The air pump is a single acting bucket plunger pump, driven by a crank shaft, turned by the engine, which is a single cylinder compound automatic cut-off engine, and also drives the boiler feed pump; it is of the trunk pattern, and the small space around the trunk on the top side of the piston forms the high pressure cylinder. Steam is admitted to the high pressure side, at boiler pressure, and is cut off and expanded and exhausted into the receiver, whence it is admitted under the bottom side of the piston, where it is again cut off and expanded, finally exhausting into the condenser.
The piston makes the down stroke when the air pump makes the up stroke; and it will be seen by referring to the cut that the engine does nearly all its work when making the downward stroke. When steam is acting on the top side of piston at high pressure, the vacuum at the same time is pulling on the full area of the piston underneath.
Fig. 356.
When the engine makes the up stroke, the steam at low pressure from the receiver acts to push the piston up; and as the air pump is doing no work then, being on its down stroke, the only work of the engine is to keep the machine up to speed.
