132 Operation of single jaw and pawl coupling

With the trailer kingpin uncoupled, the jaw will be held open by the pawl in readiness for coupling (Fig. l.24(a)). When coupling the tractor to the trailer, the jaw of the fifth wheel strikes the kingpin of the trailer and swivels the jaw about its pivot pin against the return spring, slightly pushing out the pawl (Fig. l.24(b)). Further rearward movement of the tractor towards the trailer will swing the jaw round until it traps and encloses the kingpin. The spring load notched pawl will then snap over the jaw projection to lock the kingpin in the coupling position (Fig. l.24(c)). The securing pin should then be inserted through the pull lever and table eye holes. When the tractor is driving forward, the reaction on the kingpin increases the locking force between the jaw projection and the notched pawl.

To disconnect the coupling, lift out the securing pin and pull the release hand lever fully out (Fig. l.24(d)). With both the tractor and trailer stationary, the majority of the locking force applied to notched pawl will be removed so that with very little effort, the pawl is able to swing clear of the jaw in readiness for uncoupling, that is, by just driving the tractor away from the trailer. Thus the jaw will simply swivel allowing the kingpin to pull out and away from the jaw.

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