When dealing with such materials as malt and grain, it is an advantage to be able to inspect the material entering the receiver, and at least one maker secures this advantage by constructing the chamber of a glass cylinder to which are bolted cast iron top and bottom pieces carrying the necessary pipe connections and discharge valves. Fig. 8 illustrates this construction and also shows fairly clearly the method of driving or revolving the discharge valves. The top flange of the valve has a worm wheel tooth cut around its periphery and the actuating worm engages in this wheel, thereby obtaining a large reduction in speed. In other words, the worm can be driven by a light, high speed belt and pulley, and still revolve the valve at a very low speed; such gearing is smooth, silent running, and altogether admirable for such a purpose as the one under consideration.
Fig. 8.—Fixed Discharger with Glass Receiver.
A very common form of separator, which is used almost invariably on plants dealing with wood shavings, sawdust and similar materials, is known as the cyclone or centrifugal separator. This is usually constructed with a sheet steel body with the inlet for the dust-laden air at the top, and so arranged that the air enters tangentially. Inside there is a smaller cylinder of sheet steel forming an air outlet, and the laden air sweeps round the annular space between the body and the inner cylinder. This results in a whirling action and the material entrained in the air is projected by centrifugal force against the side of the separator body. In some instances an internal ledge, or plate of “corkscrew” form, leads the material downwards towards the outlet at the bottom of the separator.
In the case of some of the denser materials which can be conveyed by air, it is sufficient to connect the discharge pipe to an open bin or chamber, the material in such cases being heavy enough to separate itself by the action of gravity.
Mr. Gordon S. Layton, describing dischargers in his paper, before the Engineering Group of the Society of Chemical Industry (Birmingham, April, 1920), stated—
“There are two types of dischargers in use: The first consists of a large steel box divided into two compartments. This box is arranged to oscillate about a horizontal axis, so that each compartment alternately is brought under the lower opening of the receiver vessel.
“The other type of discharger consists of a bucket wheel rotating continuously inside a closely fitting casing. The material which is being conveyed falls into the pockets of the bucket wheel when these are on the top of their revolution, and is passed out through an opening in the lower side of the casing.
“It will be obvious that the working of both types is liable to be interrupted by the jamming of a foreign body (such as a piece of wood or a bolt) in the working parts; in each case, special mechanism for driving the discharger has been devised, to avoid the interruption resulting from such blocking, and to enable the discharger to keep on working continuously.”
The rotary type of discharger is preferable to the tipping box type, for the following reasons: because the rotary discharger is more easily kept air-tight, works without vibration, and gives a practically continuous stream, whereas the discharge from the tipping box occurs as large isolated masses of material.