The “Acme” type of fixed spray, manufactured by the Ames Crosta Sanitary Engineering Company, is shown in [Fig. 115]. The special feature of this spray is that it has a loose metallic cone, which is provided with a helical groove, inside the nozzle. This cone rotates as the sewage passes through the nozzle, and thus gives a maximum spray with a small head. These sprays have a free waterway, and the rotation of the cone tends to prevent the choking of the orifice.
A simple form of fixed spray consists of perforated pipes arranged at suitable intervals over the surface of a filter, and provided with dosing apparatus to give intermittent supply under pressure, and thus deliver the sewage in the form of jets from the perforations in the pipes. An improved form of this type of distribution is supplied by the Septic Tank Company. This is illustrated in [Fig. 116], from which it will be seen that orifices in the top of the distributing pipes are fitted with nozzles, set at an angle of about 45 degrees to the vertical. The discharge from these nozzles, it is claimed, gives the maximum efficiency of distribution.
Fig. 116.—Fixed Spray Jet.
Fig. 117.—“Carlton” Adjustable Fixed Spray.
A self-cleansing spray jet has been brought out by the Carlton Engineering Co. From the illustration, [Fig. 117], it will be seen that a plug B is fitted into the orifice and supported upon a spindle, which is attached at its lower end to a lever connected to an automatic tipper on the outside of the nozzle. The tipper is fed by the spray from the nozzle, and as it falls alternately on one side and on the other it raises and lowers the plug B in the orifice, which tends to prevent any clogging, and also varies the area of the orifice and the rate of discharge, as well as the area of the filter-surface covered by the spray.