Drawbar (haulage)

This article is about haulage. For other uses, see Drawbar (disambiguation).
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A large ballast tractor pulling a load using a drawbar
General duty drawbar system on a truck

A drawbar is a solid coupling between a hauling vehicle and its hauled load. Drawbars are in common use with rail transport, road trailers, both large and small, industrial and recreational, and with agricultural equipment.

Agriculture

Agricultural equipment is hauled by a tractor mounted drawbar. Specialist agricultural tools such as ploughs are attached to specialist drawbars which have functions in addition to transmitting tractive force.

Road

A drawbar is mounted or located on the tractive vehicle and is used to accept the coupling of the load. The direction of haulage may be push or pull, though pushing tends to be for a pair of ballast tractors working one pulling and the other pushing an exceptional load on a specialist trailer.

The drawbar should not be confused with the fifth wheel coupling. The drawbar requires a trailer which either loads the drawbar lightly (for example a small boat trailer, or caravan, where a load of up to ~50 kg (110 lb) is part of correct trailer loading practice), or the load is the weight of the coupling components only (larger trailers, usually but not always with a steerable hauled axle, front or rear). By contrast, the fifth wheel is designed to transmit a major proportion of the load's weight to the hauling vehicle.

Rail

Two or more passenger cars or freight cars may be attached by means of a drawbar. At both extremes there is a regular coupler such as the North American Janney coupler or the Russian SA3 coupler. This drawbar eliminates slack action.

The simplified scheme of the SA-3 automatic couplers.
An animation of the SA-3 coupler

See also

References

    • US 6739402  Transport drawbar
    • US 5096075  Slackless drawbar assembly with gravity responsive wedge (rail application)
    • US 5598937  Slackless drawbar assembly (rail application)
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