13G OF THE GENERATION AND [SECT. in. 



will be forced up the feed pipe by the pressure of the steam, and be driven out 

 at the valve. 



For water at 60, 2'94 feet in height is equivalent to 1 Ib. on the circular 

 inch, but the water in the feed pipe will generally be nearly 212, and then 

 3 feet is required. Hence, three feet in height for each pound per circular inch is 

 the proper height. 



The stone float should obviously be in that part of the boiler where it will be 

 least disturbed by the formation of steam ; and the feed pipe should deliver its 

 supplies as far from the point where the steam is principally generated as possible. 

 253. On account of the force of steam required in high pressure engines, an 

 ordinary feed pipe cannot be applied to supply the boiler, without making it of 

 a very inconvenient height : water is therefore supplied to the boiler by a small 

 forcing pump, worked by a lever connected with one of the reciprocating parts 

 of the engine; and this water, instead of passing immediately into the boiler, should 

 pass through a pipe or receptacle which traverses back and forward in the steam 

 which escapes from the engine, so as to become considerably heated before it 

 enters the boiler, that it may not check the production of steam. A much better 

 method, however, is to make the smoke pass round and heat a small supply 

 boiler, which should have a communication with the proper boiler. The pump 

 in the former case supplies the small boiler. 



In supplying a boiler by a pump worked by the engine, the same supply is 

 given at all times, whatever may be the quantity converted into steam and used. 

 Now as the consumption of steam is variable, the quantity injected by the pump 

 must often be in excess. This may be remedied by the use of a float, in land 

 engines. Let A, B, (Fig. 2. Plate i.) be two connected valves, in the box which 

 receives the water from the pump, the one A opening to the boiler, the other B 

 opening to the waste pipe. If the stem of these valves be connected to the lever 

 of a balanced float, as indicated in the figure, the increase of water in the boiler 

 above its proper level will cause the valves to descend, and close the communica- 

 tion to the boiler, while the waste valve opens and admits the superfluous water 

 to run off by the pipe. In this construction the boiler will receive the supply 

 from the pump regularly at all times, except where it is in excess for the quantity 

 used, and then the float F rises, and shuts the passage of entrance to the boiler, 

 and opens the one to the waste, till the quantity no longer exceeds the consump- 

 tion. This simple arrangement renders the feed regular, which is of much 

 importance. l 



1 In the early boilers of Mr. Watt, a whistle was attached : the pipe connected with the whistle 

 descended through an orifice in the top of the boiler to a few inches below the proper level at 



