Servicing Equipment of the Hydraulic Type
Page 54
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The Hydraulic Principle Used in Jacks, Vehicle Lifts and Brake Testers
ACONCERN which is making good progress with the production of hydraulic appliances for use in conjunction with commercial vehicles is Henry Miller. and Co., and we have recently visited this company's works at 186, Walmer Road, London, W.11, to witness the manufacturing processes used in connection with the different types of equipment made.
The new Skyhi brake tester employs the hydraulic principle not only to measure the brake efficiency on each road wheel, but also to indicate the pressure applied to the brake pedal when the efficiency readings are being taken. The procedure is to jack up all four wheels; positive depression of the brake pedal is then effected by a hydraulic ram fixed to the steering column and adjustable for any reasonably placed brake pedal. This ram has a gauge graduated up to 200 lb. and it is operated by a wing nut. Around the periphery of each tyre is then fitted a steel band that is tightened by means of a chain and a lockable sprocket.
Overcoming Brake Resistance.
The sprocket housing is of malleable iron, and in fitting the band it is Placed at the back of the wheel slightly below the hub level. Beneath this casting is then placed a kind of hydraulic jack with a gauge which reads up to 1,200 lb. This indicates the pressure required to overcome the resistance of the brake shoes. It enables pressure on the four B40 wheels to be balanced to a nicety. To obtain readings for different positions of the drums the band is slacked off and refitted. The complete outfit is marketed in one model to suit all commercial vehicles and the list price is £18 18s.
This brake tester is very conveniently employed in conjunction with the Skyhi hydraulic lift, which is made in singleram and multi-ram patterns. The single-ram type is, perhaps, the best known, and it has the advantage that the lift may be used as a turntable. Standard models are available for loads of three, five or seven tons, the prices being respectively £117 10s., £137 and £152. Installation is ,very simple, the base of the telescopic ram being bedded in concrete, for which a hole of only reasonable size • need be dug. Actuation is purely by hydraulic means, a British 2 h.p. electric motor being employed in conjunction with a high-pressure oil pump of special design incorporating Hoffman ball beatings throughout for radial and thrust loads. The bridge is made of steel girders and carries four adjustable chocks on which the axles ma'y be rested if it be necessary to jack the wheels clear of the ramps for brake-testing or other purposes. A release valve is provided to obviate all risk of the ram bursting by reason of overload.
The 3-ton model has a track length of 16 ft. 6 ins., an inside width of 3 ft. and an outside width of 5 ft. 8 ins. In the case of the five-tanner these dimensions are respectively 19 ft., 3 ft. 10 ins. and 7 ft. 2 ins., and in the case of the seven-tonner they are 21 ft., 3 ft. 8 ins. and 7 ft. 8 ins.
Types of Hydraulic Jack.
Assimilar safety device is incorporated in all the models of Skyhi hydraulic jack for commercial motors. These are made for any load that it is required to lift ; to give an example, 15-ton jacks are supplied to the Underground Railway, and the London General Omnibus Co., Ltd., uses considerable numbers of the model 373 4-ton jack, not only for garage purposes but also for its coaches. The list price of this model, which is of the two-stage telescopic type, is £8 8s. The single-stage 4-ton model is listed at 1.6 Os. For heavy commercial motors the model 810 8-ton jack, selling at £8 8s., is suitable for garage and service use, for it can be made In any• reasonable height to meet requirements. The 10-ton model, with dual pumps and
handle for carrying, can be made with any initial height and is listed at £12 12s.