3. A small double cylinder engine operating either a pinion and rack as above described, or revolving a drum with a chain attached to it, and the rear end of the dipper handle as described in the first case.
4. A long steam cylinder attached to the dipper handle, whose piston rod is connected to the dipper, extending or withdrawing it as desired.
FIG. 5.—VICTOR STEAM SHOVEL; Toledo Foundry & Machine Co., Toledo, O.
The thrusting mechanism used in the last two cases imparts a rapid, steady and powerful motion, but the extra engines or steam cylinder and their connecting steam pipes involve a complication which often more than balances their advantages.
Swinging the crane in a horizontal direction is generally accomplished in one of the following three ways:
1. A chain passing around the swinging circle attached to the post, and wound around drums connected to the engine by positive gearing or friction clutches.
2. A wire rope passing round the swinging circle and connected to the piston rods operated by two long steam cylinders.
3. A chain passing round the swinging circle and wound around a drum connected to a small reversible engine.