. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 126 BULLETIN 711, U. S. DEPARTMENT OF AGEICULTUEE. The main engine, or what is known as the skidding engine, has 12 by 12 inch cylinders and three drums. The back drum, the one next* to the boilers, is known as the slddding line drum. This drum hauls the log in. The middle drum is known as the return or trip line drum. This is used not only to haul the carriage back to the woods but to hold the carriage in proper position when the log is being yarded under the carriage, also to regulate the speed of travel of the load
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 126 BULLETIN 711, U. S. DEPARTMENT OF AGEICULTUEE. The main engine, or what is known as the skidding engine, has 12 by 12 inch cylinders and three drums. The back drum, the one next* to the boilers, is known as the slddding line drum. This drum hauls the log in. The middle drum is known as the return or trip line drum. This is used not only to haul the carriage back to the woods but to hold the carriage in proper position when the log is being yarded under the carriage, also to regulate the speed of travel of the load when gravity carries it forward. The return line drum is pro- vided with an interlocking and reversing device, which permits the interlocking of the skidder and receding line drum after the ends of the logs have been elevated sufficiently to clear obstructions. By means of this device the return line is paid out automatically as the skidding line is drawn in. The third drum from the boiler is the slack-pulling drum, which enables the engineer to pay out from the carriage the length of skidding line that is necessary to reach the logs that lie to one side or the other of the overhead cable. The slack- oiaf£_. Fig. 40.—Skidding carriage, Lidgerwood overhead system. pulling drum has a friction device set with a tension of about 500 pounds, so that the line will not hang slack. The loading engine has double cylinders and four drums, two friction and two clutch drums. The friction drums are used in loading, but only one of them at a time. The two make it possible to shift the loading line from one side to the other, so that it is unnec- essary for the loading engineer to look over the machine when loading is in progress. The two clutch drums are used for raising the main cable, rigging, etc. The machine, as a rule, is mounted on a steel car, which is 22 by 8 feet and is equipped with a jack at each corner and swivel trucks. With this equipment it is possible to jack up the car, t
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