Information AboutSemi-trailer |
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A semi-trailer is a Trailer without a front axle. A large proportion of its weight is supported either by a Road Tractor or by a detachable front axle assembly known as a Dolly . A semi-trailer is normally equipped with legs which can be lowered to support it when it is uncoupled. A Road Tractor coupled to a semi-trailer is often called a Semi-trailer Truck or ''semi''. Though most road trailers meet this definition, the term is most often applied to heavy trailers appropriate for use in such a rig. ADVANTAGES AND DISADVANTAGES .]] Advantages In Road Haulage semi-trailers predominate over Full Trailer s because of their flexibility in use.
Disadvantages
COUPLINGS There are two types of couplings: fifth wheel and '''automatic'''. In some applications, no separable coupling is fitted and the trailer is bolted to the tractor unit using a bearing and rocker feet as are used under a fifth wheel ''skid plate''. Fifth wheel coupling The towing vehicle has a wide coupling plate known as a Fifth Wheel Coupling bolted onto its chassis on which the semi-trailer rests and pivots. As the tractor reverses under the trailer, a king-pin under the front of the trailer slides into a slot in the skidplate and the jaws of the fifth wheel close on to it. The driver has to raise the trailer legs manually and couple the airbrake lines and electrical cable. On tractor-trailers that have different colored lines, the red and blue lines are air lines used in brake operations, and the green one is the electrical line. Automatic couplings Many years ago automatic couplings predominated but are now quite rare. Automatic couplings were generally used for payloads of 12 tons or less, e.g. on the Scammell Mechanical Horse . There is no coupling plate on the tractor. There is a turntable permanently fixed to the underside of the trailer. This locks on to the chassis of the tractor. When the tractor reverses under the trailer its legs rise and the brake and electrical connections are made automatically. Almost the entire coupling and uncoupling procedure is operated by the driver from inside the cab, except that he or she has to descend to release (or apply) the trailer parking brake. BATTERY SEMI-TRAILER A battery propulsion semi-trailer is a semi-trailer that contains the batteries that are used to power an electric truck or bus. TYPES Different types of semi-trailers are designed to haul different cargoes. ;Box :The most common type of trailer can haul almost anything that can fit inside. Also called a van trailer. ; Reefer - see Refrigerator Truck :Box trailer with a heating/cooling unit (reefer) attached. Used for hauling produce, ice cream, etc. ;Tanker - see Tank Truck :Used for hauling liquids like gasoline, milk, etc. ;Dry Bulk :Resembles a big tanker, but is used for sugar, flour and other dry powder materials. ;Flatbed :Consists of just a load floor and removable side rails, and a bulkhead in front to protect the tractor in the event of a load shift. Can haul almost anything that can be stacked on and strapped down. ;Lowboy :Type of flatbed in which the load floor is as close to the ground as possible. Most commonly used to haul heavy equipment, cranes, bulldozers, etc. ;Car carrying trailer :Carries multiple cars; usually new cars from the manufacturer. SEE ALSO
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