XXVIII. J. DAVIS. 



MACHINERY. 



At present the air compressing plant consists of two Parker 

 continuous current shunt wound motors actuating two air com- 

 pressors. Space has been left for the duplication of this 

 machinery when an extension of the sewerage system requires it. 



The motors are each capable of developing 25 H.P. at a speed 

 of 470 to 500 revs, per minute, when supplied with a current 

 pressure of 500 volts. One motor is, therefore, when running at 

 full speed, capable of performing the whole work. 



By arrangement with the Railway Commissioners, the electrical 

 energy is supplied through a 19/16 in. cable from the power house 

 at Rushcutter's Bay at a cost of ljd. per B.T. unit. 



The air compressors are similar in every respect to that at 

 Willoughby Bay. 



The air receivers are of mild steel, with segmental ends, 

 4 ft. 6 in. internal diameter, and 9 ft. high. They are fitted 

 with manholes and dead weight safety valves, regulated to blow 

 off at 35 lbs. pressure. 



The inlet and outlet pipes are 6 ft. diameter, the former 

 extending upward in the centre of the vessel about 5 ft., and the 

 latter has its mouth protected by a cast iron baffle. The spray 

 water by these means is separated from the air and discharged 

 by a trapped drain pipe in the usual way. 



The motors and compressors, by working in parallel or series, 

 can be run at half or full speed. To accomplish this, and also to 

 ensure the safe starting of the motors against a maximum load, 

 a series-parallel controller has been designed, which allows the 

 current at starting to pass through a series of resistances, which 

 are cut out step by step. 



As the work to be performed is so variable, necessitating the 

 air compressor being run to suit the flow of sewage, it was 

 considered prudent to introduce means by which, when the 

 pressure had either risen or fallen between certain fixed limits, 

 the machinery would be automatically stopped or started. 



The maximum pressure decided on was 30 lbs., and the 

 minimum 22 lbs , the latter being the smallest pressure which 



