A simple and it is claimed an effective air brake for motor trucks and trailers is now being marketed by an air-brake concern of San Francisco but it has not yet been tried out in the logging industry. “Braking action is secured by means of a diaphragm and pressure plate. The diaphragm is directly connected to the brake-band lever. No air compressor is used in this system. A small air receiver or storage tank takes the spent gases from one of the cylinders by utilizing the outlet afforded by a priming cock. The brakes are applied by a control system mounted on the steering column. By means of a quickly adjusted hose connection, air can be applied to the wheels of the trailer using the control which governs the braking of the truck. The air pressure in the storage tank is automatically maintained by means of an accumulator valve which closes when the tank pressure reaches 150 to 175 pounds. If the tank should be empty at the top of a long grade, sufficient pressure is generated by the compression of the engine to operate the brakes. Opening the throttle to full emergency position will apply maximum braking effect without sliding the wheels.”[6]
[6] Air Brakes for Trucks. Timberman. March, 1920. Page 48g.
This system has not been tried out under the conditions as found in the woods but if it can be made to work satisfactorily it will be a big improvement over the old system as the driver will then have instantaneous control over the load at all times.
LIFE AND DEPRECIATION
The life of the trailer is about the same as that of the truck, and in depreciation, a period of four years is usually allowed. The maintenance and upkeep of the trailer is very low. It rarely gives out and with the ordinary usage requires only a few minor repairs every two or three years.
COST DATA
The items of expense are here segregated in such a manner that they may be used as a basis for figuring the cost of hauling logs under average conditions. These costs are for the truck and trailer as a unit. If a road has to be built, the overhead charge of the road per thousand feet of timber hauled over it together with the cost of upkeep must be added to the figures given below in order to know the total cost of transportation per thousand feet.