104 SOME EEMARKS ON SEWERAGE SYSTEMS. 



ventilator^ is Keeling^s, which, by a gas-Jet burning in a 

 lamp-post, both induces a current and burns much of the 

 foul air. Cowls have often been placed on ventilating 

 shafts to regulate the air currents, with more or less success. 

 In connection with these, flaps are often used to divide 

 sewers into sections, and also to prevent wind draughts 

 through them. 



With regard to all ventilators, it is necessary to remem- 

 ber, that to be eiBcient they must be of ample sectional 

 area, equal, or nearly equal, to the area of the sewer which 

 they ventilate. 



So far I have endeavoured to describe an ordinary gravi- 

 tation system of sewerage. It often happens that on 

 account of levels it is impossible to deliver the sewage at 

 the outfall without recourse to pumping. 



Of pumps there is almost every conceivable variety in use, 

 from the steam-direct acting pump to the hydraulic engine. 

 One of the latest designs is Shone^s Pneumatic Ejector, 

 which will be touched upon hereafter. So far, the most 

 economical, where the flow of sewage does not vary to a 

 very large degree, is the direct-acting steam-pump (^^e., with 

 steam cylinder piston working direct into the pump baiTel), 

 in which the valves are made specially large and get-at-able, 

 so as to be able to pass or clear any large and coarse substance. 



In all such cases, however, it is found necessary to pass 

 the sewage through a screen, to remove all the larger sub- 

 stances ; and it is understood that the pump has a sufficient 

 quantity of sewage to raise to enable it to work at its 

 greatest efficiency. It is easy to arrive at the probable 

 quantity of sewage per twenty -four hours, especially if the 

 population be provided with a systematic water supply ; but 

 it is generally found that of this quantity about one-half 

 flows off during six hours of the morning, and that the flow 



