Shock Absorbers' Contribution to Ambulance Efficiency
Page 44
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I T is not unusual for shock absorbers to be a standard feature of high-class ambulances, and there is, on this type of vehicle, a special need for these items of chassis equipment. Even on machines with suspension systems designed expressly to afford the smooth travel that should be a leading characteristic where the injured or sick have to be transported at the highest practicable speed, shock absorbers are desirable. How much more so, there fore, on vehicles designed originally for goods carrying which have been converted for ambulance work.
With the big increase that has recently taken place in the production of ambulances, both built for that pun pose from the outset and converted from standard goods or passenger vehicles, there has arisen a new application of the shock absorber, which device is not commonly included in the specification of the ordinary goods chassis above a moderate capacity.
Accordingly, a brief description of the products of a leading shock-absorber maker, which has, we believe, supplied this type of equipment for practically every record-making car of recent years, seems appropriate. We refer to Andre (Components), Ltd., Felsham Road, Putney, London, S.W.15, manufacturer of the Andre Hartford and Andre Telecontrol devices.
Both are of the friction type and are designed to offer a degree of resistance to upward as well as downward spring movement. They are, dampers, pure and simple, and, broadly, control spring action by damping out recoil or oscillation.
The two types differ in that the former is regulated by an adjustment on the shock absorber itself, which is set prior to taking the vehicle on the road, whilst the latter is controlled, through the medium of an hydraulic System, from the dashboard, so that the friction can be varied while the vehicle is in motion.
In both cases the absorber unit comprises a number of friction discs, of Anduro weather-proof material, working between stainless-steel plates, alternate ones being in egidl with the two shock-absorber arms. The knuckle action of the last named, at their points of attachment to the chassis, is afforded by Silentbloc bearings.
Springs of adjustable strength regulate the pressure on the plates of the Hartford devices, whilst an elastic hydraulic chamber imparts the pressure in the case of Telecontrol absorbers. From this chamber a copper pipe-line runs to the master control on the dashboard.
To permit the angular motion necessary where the tube passes from shock absorber to frame, there is a multiple coil, which reduces the pipe movement to an amount well under that allowed by the elasticity of its metal.
One regulator may control all four shock absorbers, or two may be used— one for each pair. The device consists of a cylinder containing, as in the absorber, an elastic chamber, and having at one end a screw plunger. Rotation of the knob operating this reduces the volume of the chamber and creates pressure in the system.
A gauge is provided to indicate the degree of pressure and a further fitment is a topping-up pump. In point of fact the system, being hermetically sealed, loses no fluid, but the device is necessary for initial charging, and to replenish it after bleeding, or in the unlikely event of a leak having developed.
This unit comprises a reservoir and small pump, the ball valve of the latter being sealed by screwing down the plunger when th.1 pump is not in use. In connection with the fluid, this is a 30 per cent. solution of pure glycerine in distilled water. Oil must on no account be used. Water alone would actually serve satisfactorily except in frost, and the sole object of the glycerine is to prevent the formation of ice.
With regard to the application of Andre shock absorbers to ambulances, the advantages of the Telecontrol type are particularly marked. The driver is not only enabled to adjust the setting to suit the load—the vehicle may be running light or with full or part complement of patients—hut also can modify the action of the damping devices according to the nature of the road surface over which he is travelling. The welfare of the passengers is thus greatly enhanced, as well as its stability when proceeding, perhaps at high speed, to pick up the cases.
Three main models of the Telecontrol apparatus are available, and they can be employed on trailers, or light or heavy ambulances. Advice on the type selected for any specific vehicle should be obtained from the maker. The price ranges from about £0 to £9 per pair, and includes the cost of all the pertinent apparatus—regulator, filling pump, gauge, piping, brackets, etc.