NOTABLE ADVANCES IN MODERN STEAMERS.
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A New 6-ton Allchin Chrertype Wagon with Three Speeds and Ackerman Steering. First Public Appearance of a Special Boiler Adopted on the Garrett Undertype.
A MONGST the particularly interest ing exhibits at the recent Brewers' Exhibition held at the Royal Agricultural Ralf, were two which deserved especial mention, as they indicated the progress which is being made in the development of the modern steam wagon. We refer to the Garrett undertype, with its somewhat novel boiler, andthe new Allchin 6-ton overtype steam wagon.
It is not very long since we participated in 'a trial run made with the former .vehicle, but at that time the boiler used was of a temporary natuee, and, although we gave certain details regarding the type which would eventually be fitted, we were unable to illustrate it or to enter into particulars. It is of the vertical water-tube type, and embodies details which are found on both Sentinel and Atkinson machines, whilst combining with these the very commendable features of unusual accessibility and increased heating area.
The boiler is built up on a stout foundation ring, and is so arranged that by merely removing the large square plate at the front. all the tubes, which slope down to the back, are rendered accessible either for reneival or for clean ing, the latter process being a matter of a few hours' work only, which is facilitated by the provision of a smaller door at the back.
The construction has eliminated the need for stays, and welded joints have been reduced to a. minimum. It is designed with a working pressure of 250 lb. per sq. in., but is hydraulically tested before use to 450 lb. per sq. in The firing is done through the foot-. plate, the fuel passing down an inclined elute into the firebox. Incorporated in the design of the boiler is an efficient superheater, which consists of a number of tubes, suitably bent to give a large heating area and situated in the smokcbox. The tubes are of solid drawn-steel expanded into east-steel headers, and the heating surface is sufficient to raise the temperature of the steam by 100 degrees F. The boiler fittings are of very solid construction, and include Safety valve, steam-pressure gauge, water gauge, injector, feed-check valve and blow-off cock. The injector is situated some little distance from the boiler so that it cannot become hot and refuse to work.
The nest of water tubes comprises 60 of 11-in. diameter, and it is claimed that the complete boiler has an unusually large steaming capacity.
For the sake of these who have' not seen our previous description, we will enumerate the chief points of the complete vehicle. The chassis is of pressedsteel, of ample section, and tapered. to front and rear. The engine consists of two high-pressure' cylinders, the steam to which is distributed by means of piston valves operated by Joy gear. This eliminates the sometimes troublesome eccentrics. It is of the horizontal, double-acting type, with the crankshaft supported on Timken roller bearings. The whole unit is in an oil-tight casing, which also holds the two-speed gear and differential.
Lubrication of the cylinders is attended to by a' mechanically operated lubricator arranged in the cab, whilst, the working parts of the engine receive their oil by splash from the bath; and to ensure the coerect quantity of lubricant being kept in this bath an oil gauge and inspection doors are provided in the crankcase.
The differential countershaft is also supported in Timken roller bearings, and the transmission-from it to the driving wheels is effected by two heavy roller chains. The feed pump, which is arranged outside the chassis frame, is controlled from the steering column, and is driven through a reduction gearing from the engine crankshaft.
The control for the wagon is by means af a stop valve fitted to the boiler, and operated by an accelerator pedal. The brakes are particularly efficient, the foot and hand brakes having side by-skle shoes acting on a single drum in each rear wheel.
The Allchin wagon, made by Wm. All. chin, Ltd., of Globe Works, 'Northampton; is a great improvement on the 5-ton
model built previously. It has three speeds against the two formerly utilized, and the erearing is arranged so that the fast-speed pinion is right up against the crankshaft bearing, thus there is practically no overhang. The gearing permits normal speeds of 12, 8 and 4 m.p.h., and the pinions are thrown into mesh by means of two levers with a special locking arrangement, which prevents any risk of two speeds being engaged simultaneously, The engine closely resembles the old model, but, has larger cylinders, these being q ins., diameter and 7* ins. dia
meter respectively by 8 ins. stroke, ana the three-way cock allows them to be changed from compound working to double high-pressure when extra power is. desired. The-valve motion is of the well-known Stephenson link type, amid is very stoutly constructed.
The safety valve used to be at the top of the cylinders, but this arrangement has been altered, and the valve is now supported on a right-angle pipe pro)ecting from the front of the engine. this obviates the obstruction of the driver's view, which previously occurred. The loco-terpe boiler is of the same cepacity, but it has been improved by lagging the outside of the firebox with sheet asbestos. This has resulted in a considerable reduction in fuel consumption.
A feed-water heater of very simple type, comprising two straight tubes in the amokebox, is now fitted as standard. The water pump is a new-pattern plunger type, gear driven from the crankshaft, the reduction being 1 to 3. This pump was formerly held to the boiler by studs, but it is now attached to the frame-member supporting the fire box. • •
The strainer between the water tank and tbe pump and injector, used to be under the footplate, . where it was very inaccessible, and when it was necessary to turn off the water, as in the event of frosty weather, it involved the operator lying on his back for this purpose. 'lie strainer is now at. the side of the tank in a very accessible position.
The fuel consumption is said to be 20-25 miles per cwt. when running on Welsh coal and with a 6-ton load. One important alteration is the use of Ackerman-type steering. This embodies a bell. orank lever connected by a cross-rod to the off side steering arm.
Few alterations have been made in the rear axle, but both brakes now operate on drums bolted to the road wheels. Each is of the external-contracting type; one acts on the near-side wheel and the other on that at the off side. Provision has also been made on the axle for the fitting of e-third brake if required. Previously the brakes were arranged so that one acted on a rear wheel and the other on the axle. The differential locking device, which sometimes proves very useful when running in soft ground, is retained.
Careful attention has been paid to springing. The front cross-spring is longer, whilst at the rear the semiellipties are each fitted with a supplementary laminated spring, which comes into action when a 4-ton load is carried, or if there be excessive deflection, due to road shock while running with a smaller load. This form of graduated springing has often been recommended in this Journal, as it obviates to a great extent the harsh running which is almost always felt when a; vehicle is running unloaded or with a comparatively light load.
The comfort of the driver has by no
meane been neglected, as the cab_ has been considerably modified. It is now wide, and equipped with side doom and two comfortable seats, one at each side.