150 C. W. DARLEY. 



demonstrated fully what could be done in this way. The pro- 

 portion between the pumps and steam cylinders in that case being 

 such that the water pressure is just about half the boiler pressure. 

 If the engineer desires to keep about forty-five pounds pressure in 

 the main he must maintain ninety pounds pressure in the boiler. 



When the pressure in the main rises anything over forty-five 

 pounds through closing valves or otherwise, the engine simply stops 

 and having no stored energy no harm results, but upon drawing 

 off a few gallons the engine again starts to replenish what has 

 been drawn off. In this case although the service tank only has 

 a head of about seventy feet, in time of necessity the pressure in 

 the main can be raised equal to that from a head of one hundred 

 and five feet, which is sufficient for all practical purposes in 

 country towns. 



It is almost indispensable that a Service Reservoir should in all 

 cases be lined throughout either with concrete, brick, or hammered 

 stone pitching, for the purpose of facilitating cleansing and wash- 

 ing out, which, in the case of Reservoirs fed by pumping direct 

 from rivers, must be frequently done, especially during seasons 

 when the river may be flooded. 



Were the lining omitted not only would washing out or cleans- 

 ing be rendered almost impossible, but the water would be con- 

 taminated and discoloured by the wash on the muddy slopes and 

 bottom, for it must be borne in mind that unless an unusually 

 large Service Reservoir is constructed the water level must be 

 rapidly altering its level every day. 



In America it is usual to construct a Service Reservoir receiv- 

 ing water from such rivers as the Mississippi, Ohio, &c, with as 

 large an area as possible and comparatively shallow, and thus they 

 fill the double duty of Service Reservoir and Settling Tank. It 

 is not an uncommon occurrence to see a deposit of as much as four 

 feet of silt in one of these Reservoirs after a few months pumping 

 in Spring. 



The position of the Reservoir must guide the engineer as to 

 whether it should be covered or not, — in most cases it is desirable 



