Fig. 27.—Tube Central in Wholesale Drug House, Distributing Orders to all Departments.
Fig. 28.—Lamson Distributing Station in well-known Publishing House.
In 1840 a pneumatic railway was actually built and worked between London and Croydon, and in view of its success was followed by others between Dalkey and Kingstown and between Exeter and Plymouth. From this it will be seen that transportation by pneumatic means is not modern in its application, and was originally intended for very large tubes and weights, but modern development has been toward small tubes and light weights.
The Vacuum Cleaner. The pneumatic transporting of material in the form of dust has been brought to a very high state of perfection during recent years and an enormous number of plants is now in use, ranging from the hand-propelled machine to very large stationary equipments.
Certain hand-propelled machines have been constructed in such a way that the fan is directly operated by gearing from the running wheels, and after a few moments a very considerable speed is attained and the suction of the fan is used for lifting the dust from the surface over which the apparatus is travelling.
Numerous designs of more powerful machines actuated by hand bellows have been placed on the market and these possess the advantage that they are independent of the use of power; but it is not altogether easy to operate a machine by one hand and to manipulate the nozzle with the other.
Electrically driven machines of almost numberless designs are available. These usually employ a high speed fan of the single-stage type, but a piston pump is embodied in some designs.
In the removal of dust the same principle applies as in the conveying of heavier materials, i.e. it is not so imperative to obtain a high vacuum as it is to have a large volume of air moving at high velocity, hence the multi-stage turbine machine has distinct advantages as regards weight of material moved and economy of power.
The multi-stage exhauster consists of turbine wheels mounted on a single shaft, the air being drawn into the first wheel, from this to the second wheel and so on right through the machine, each wheel increasing the suction on the intake end according to the total number of wheels or stages. This style of machine is procurable in either the stationary or portable type, and in both it is made in various sizes, the portable machines ranging from 1/12 h.p. up to ½ h.p. for domestic purposes, and from 1½ to 3 h.p. on trucks for cleaning electrical machinery, railway carriages, etc. Figs. 29 and 30 illustrate typical stationary and portable plants respectively.