A simple type of fixed spray is supplied by Messrs. George Kent, Ltd., and is shown in [Fig. 118]. In this case the liquid issuing from the nozzle impinges upon a curved surface or cone, by which it is deflected and spread out, leaving the surface at an angle of 45 degrees to the vertical. One of the advantages claimed for this type is that it has no small holes to become clogged.
Fig. 118.—Fixed Spray Nozzle.
A novel form of this type of apparatus is manufactured by Messrs. Daniel Adamson and Co. Above the orifice in the nozzle is suspended a revolving deflecting plate ([Fig. 119]). The vanes of this plate are shaped in such a way that, as it revolves, the jet impinges against a different angle every instant. None of the energy is wasted in churning or throttling, as the plate merely directs the water in such a way that no two drops ever fall twice on exactly the same spot. It is stated that the diameter of the wetted area of the filter surface is more than double the head.
Fig. 119.—Adamson’s Fixed Spray.
There are a considerable number of other types of nozzles used for fixed sprays. Several of these are illustrated in [Fig. 120], where A is the type in use at Salford; B, the type used at Birmingham; C, a nozzle with a double spreader in use at Waterbury, Conn., U.S.A.; D shows another type in use at Waterbury, with a single spreader, but this is so arranged that it can be adjusted to give a smaller or larger area of orifice. E shows the type adopted at Columbus, Ohio, U.S.A.
In connection with some elaborate studies of methods of distribution for percolating filters, which were carried out for the Sanitary Research Laboratory and Sewage Experiment Station of the Massachusetts Institute of Technology, by Messrs. Winslow, Phelps, Storey and McRae, a special series of investigations were made into the value of what is referred to as the “gravity method of spraying.” This consists in supplying the sewage from troughs or pipes supported above the filter, and discharging it through orifices on the under side of the pipes or troughs in the form of solid jets, which are made to impinge upon concave discs fixed near to the surface of the filter. The effect of this impingement is to cause the liquid to splash upwards and outwards in the form of a fine spray, and, as a result of a long series of tests with various forms of discs and various heads, it was found that the best average results were obtained with a concave metal disc 3 inches in diameter having a curvature corresponding to a radius of 2 inches. With a total head of 4 feet and a head of 3 feet from disc to the pipe above, it gave the best results obtained with that total head. With a total head of 6 feet and a head of 4 feet from disc to supply pipe, it gave the best results obtained by any of the forms of this type of distribution that were tested.