298 SEWAGE AND ITS PURIFICATION 



heads are expected to be 7" and 15". Suitable vanes may be 

 attached to the ends of the arms, and controlled by a master 

 vane, so that the wind pressure may be utilized to help the pro- 

 pelling arrangements during times of storm. 



5. Jennings' Patent Automatic Sprinkler claims among 

 special features that the arms are jointless, and carried on 

 protected ball-bearings, and that the loss of head in the 

 Distributor itself is negligible. The centre tank T (Fig. 46) is 

 fixed, and the arms alone rotate, their weight being carried on 

 the moving vertical shaft S, which runs on ball-bearings. 

 An overdraw syphon O supplies each arm from the central 

 tank. The syphon is kept full by water traps at the inlet and 

 outlet ends, but it has to be filled in the first place by means 

 of a pump. The perforations in the arms are arranged with 



Fig. 46. — Jennings' Patent Automatic Sprinkler for Sewage and Water Filtration, 



the object of distributing equally over each sq. yd. of filtering 

 area. The feed supply F to the central tank T, through the 

 underground pipe A, is regulated by an automatic syphon D, 

 governed according to the volume of sewage by a syphon valve 

 and ball float. The head is kept constant by a weir. When 

 the flow increases two additional arms come into. operation as 

 in some other forms ; in this way it is said that the maximum 

 flow may be four times as great as the minimum. The pattern 

 shown is adapted for filters up to 50 ft. diam. ; above this size 

 a fixed central column is used. It is not explained how the 

 central bearing would be affected if one arm of the distributor 

 became filled before the other, and consequently threw the 

 distributor out of balance. Jennings' sprinklers, 80 ft. diam., 

 are in operation at the sewage works, Cole Hall, Yardley, 

 and Kenilworth, and smaller ones of 10 to 40 ft. at St. Leonards, 



