Girling Brakes for the Hands Semi-trailer
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ALIVIOST exactly a year ago we described an interesting new semi-trailer marketed by Hands (Letchworth), ,Ltd., of Letchworth. Since that time the outfit has been fully tested by a mimber of important operators, and the concern's works at Letchworth have been extended and reorganized to facilitate production.
Whilst the general design of the outfit remains unchanged, various modifications have been made since the semi-trailer was introduced and the most important, of these is, perhaps, the standardization of Girling brakes on all models.
This?system is used extensively on private cars ; it has also been adapted for trolleybuses in the Girling-Peters layout, and its use on goods vehicles has been forecast by this journal. Although several important chassis makers have experimental set-ups in use, we believe theHands semi-trailer to be the first goods .machine on which Girling brakes are the standard fitment.
Important advantages are claimed for the Girling brake and these appear to be fully borne out in practice. It is of simple design, the shoes being expanded by a wedge bearing against rollers, outside these being plungers on which the shoe tips bear.
This method of operation affords a high degree of efficiency and, in addition, there is the advantage that, when the wedge is not directly coupled to the power or vacnum cylinder, as in the case of the Hands semi-trailer, the intermediate gear may consist solely of rods or cables in tension, torsional cross-shafts being eliminated.
On the Hands standard semi-trailer the brakes are of the vacuum type, and the control is obtained by an ingenious regulating valve, which not only maintains a constant balance of vacuum throughout the system, but sets the time of the braking effort to give an early or delayed action in relation to the braking of the tractor unit.
An accompanying illustration shows the arrangement of the double-bogie unit for the 10-ton model, and the vacuum cylinders are to be seen forward of the transverse spring. The simple rod operating gear for the final stage is noteworthy, and each pair of brakes is fully compensated.
The trailer brakes are independently connected to the foot and hand brakes of the tractor unit and a further point is that, when the semi-trailer is uncoupled from the motive unit, the vacuum line is automatically disconnected through the medium of a patented valve, and the trailer brakes are Immediately applied. A mechanical control is provided for operating the brakes when the trailer is uncoupled from the tractor.
The Hands semi-trailer is available in two forms, one type of machine having a single axle and a further model
having a double-bogie axle. The first is marketed in two types, a 5-6-tanner and an 8-tormer, whilst the doublebogie outfit is designed for 6, 8, 10, 12 and 15-ton payloads. All models can deal with considerable, overloads and a wide safety margin has been allowed for in all the highly stressed components.
A big saving in weight has been obtained, without any loss of strength or rigidity, by the use of a central box girder to form the backbone of the frame. The crossmembers are pressed from the same material and are electrically welded to the main girders. Light side members are welded to the cross-members and these embody a profile border which carries the flooring. • No outrigger :brackets, body runners, or a sub-frame are required. The Hands concern has installed a large press and makes its own frame members so that no difficulty is encountered if a variation from the standard frame design be required. Thus, the frame may be straight, or of the semi-drop or full-drop type and the variation in the loading height of
drop-frame models may be set to any reasonable dimensions to cater for special operating conditions.
The frames are built up in a jig and are first spot welded, being then transferred to a swivelling stand. The use of the last-named piece of equipment makes every part of the frame easily accessible to the welder, and an accompanying illustration shows a frame turned on its side to facilitate welding operations.
A two-speed hydraulic lifting gear is incorporated in the head of the main frame and, in addition to fulfilling its primary function of lifting the trailer clear of the tractor, it also controls automatically the coupling gear and the braking system. The control lever provides for three positions—" closed," " pump " and "open "—and, to uncouple the trailer, the lever is placed in the " pump " position. This operation releases the locking sleeve on the turntable and allows the high gear of the pump to be brought into action.
Operation of the pump first lowers the jockey wheels, then low gear is engaged to lift the trailer clear of the motive unit, after which the brakes are automatically applied, as previously mentioned, and the rear light adapter is disconnected.
The range of lift provided is ample and, when recoupling, the trailer may be dropped inch by inch on to the turn table so that should there be any alteration in levels, due to the tractor having moved from the place where it was uncoupled, no difficulties are experienced.
Recoupling may be effected from any angle and, during this operation, the locking sleeve is masked by the turntable housing and cannot suffer damage. When the trailer is in place,. the movement of the lever to the " closed " position operates the locking sleeve, brings the brakes under control from the tractor, remakes the rear light connection and rettirns the hydraulic gear to the " off ," position.
On the double-bogie unit the springs are mounted transversely, the axle bearers being carried on large bearings fitted in the spring bosses. A feature of the design is that the axle bearers can be revolved upon their own axes so that the inside wheels can be brought to the outside position. To change the ,tyres of the inner wheels is; therefore, a simple matter, moreover, the inspection of the brakes and hubs is greatly facilitated. The single-axle machine is equipped with low-periodicity semi-elliptic springs, so constructed that no shackles are required.
These semi-trailers are light in weight, have a generous platform area, and all parts of the gear are substantially built. The design represents a serious attempt to cater for every requirement of operators who use this class of machine and the price is reasonable.