NORTH SYDNEY AND DOUBLE BAY SEWERAGE SCHEMES. XXIX. 



would lift the sewage from the ejector stations to the gravitation 

 main, and the former being as high as the pressure could be 

 economically used. Moreover, when the pressure rises above 

 30 lbs. per square inch, it seriously affects the working of the 

 valve gear in the ejectors. It became necessary, therefore, that 

 the series-parallel controller should be automatically governed, 

 so that the pressure should be maintained between these two 

 limits. In order to effect this the air pressure is admitted to 

 either end of a small cylinder, the prolongation of the piston 

 rod of which is a toothed rack, which engages a pinion on 

 the head of the controller spindle. Immediately above this 

 rack there are a series of stops cut on the bar to which the 

 rack is fixed. These stops correspond exactly with the 

 different positions the series-parallel controller must stop at 

 when cutting the resistances out step by step. The bar 

 carrying these stops passes round a die plate, so arranged that 

 only one stop can pass through the plate, the next being 

 unable to do so until the die plate has moved either up or down, 

 as the case may be. The motion is given to the die plate by 

 means of two small hydraulic cylinders, which allow it to slowly 

 travel up or down. The effect is that while the die plate is 

 slowly travelling up or down, as the case may be, immediately 

 the stops referred to coincide with the opening in the die plate 

 the pressure of air in the cylinder forces the stop through the 

 plate, and thereby the rack actuates the controller. The pauses 

 necessary for cutting out the resistances are thus secured. 



This mechanism is regulated by a valve which is constructed 

 to rise at the 22 lbs. pressure, and fall at the 30 lbs., and admit 

 the air pressure on either end of the air cylinder, and 

 simultaneously the water pressure on one hydraulic cylinder, 

 and exhaust from the other. 



There is one other detail to be thought of in stopping and 

 starting the machinery, namely, the circulating and spray water. 

 A small air cylinder, which is regulated by the valve referred to 

 above, works an equilibrium valve placed in the water service. 



