PNEUMATICS. 



downward pressure sustained by the 

 piston. 



On the other hand, the upward pres- 

 sure is produced by the weight of the 

 atmosphere pressing on the water in the 

 reservoir, and transmitted through the 

 column C B, to the lower surface of the 

 piston. But as this pressure has to sup- 

 port the column B C, we must subtract 

 from it the weight of this column, in 

 order to obtain the effective upward 

 pressure on the piston. From a column 

 of water, thirty-four feet in height, and 

 with a base equal to the section of the 

 piston, subtract as many feet as there 

 are in B C, and we shall obtain a column 

 whose weight is equal to the upward 

 pressure. This must be taken from the 

 downward pressure, and the remainder 

 will give the force required to lift the 

 piston. If from 34 + h feet we sub- 

 tract 34 feet, the remainder is h feet ; 

 but in doing this, we have subtracted 

 more than enough by the number of feet 

 in B C ; this number must, therefore, be 

 added, and the whole column whose 

 weight is lifted, has the height h + BC ; 

 that is, H"B + BC, orH"C. 



(43.) Thus it appears, that the force 

 necessary to lift the piston is the weight 

 of a column of water, whose height is 

 that of the level of the water in the 

 pump, above the level of the water in 

 the well, and whose base is equal to the 

 section of the piston. This force, there- 

 fore, from the commencement of the 

 process, continually increases, until the 

 level of the water rises to the discharg- 

 ing spout S, and thenceforward remains 

 uniform. 



(44.) To compute the actual force 

 necessary to work a pump, (exclusive of 

 the pump-rods,) therefore, let the height 

 of the discharging spout S, above the 

 level C of the water in the well, be ex- 

 pressed in feet, and let the number which 

 expresses it be h. Let half the diameter 

 of the piston, expressed in parts of a 

 foot, be r ; the section of the piston, ex- 

 pressed in parts of a square foot, will 

 thenberxrx3.14.(rzote,jo. 4.) If this be 

 multiplied by the number of feet h in the 

 height, we shall obtain the number of 

 cubic feet of water which it is necessary 

 to lift at each stroke. This is h x r x 

 r x 3.14. Each cubic foot of water 

 weighs about 1000 oz. av., or 624 Ibs. ; 

 this7 multiplied by ^xrxrx3.14, 

 will give, in pounds av., the force re- 

 quired at each stroke to lift the piston. 



The quantity of water discharged at 

 each stroke, is equal to a column of wa- 



ter, -whose base is the section of the pis- 

 ton, and whose altitude is the length of 

 the stroke. This quantity may, there- 

 fore, be found in cubic feet> by multi- 

 plying r x r x 3.14 by the number of 

 feet in the length of the stroke. The 

 weight of the water discharged may be 

 ascertained in pounds avoirdupois, by 

 multiplying this by 62, and the number 

 of imperial gallons by dividing the num- 

 ber of pounds by 10. 



II. The Lifting-Pump 

 (45.) This pump also consists of an 

 hollow cylinder A B (fig. 24 .) immersed 

 in the reservoir from & 24. 

 which the water is 

 to be raised. A 

 valve opening up- 

 wards is fixed in 

 this cylinder at V, a 

 little below the level 

 L of the water in the 

 reservoir. A piston 

 P, having also a 

 valve opening up- 

 wards, is moved in 

 this cylinder by a 

 frame F F F F, con- 

 nected with the end 

 of the piston-rod 

 PH. At the top of 

 the cylinder is a 

 spout S to discharge 

 the water elevated. 

 Let us suppose 

 the piston P at the 

 bottom B of the cy- 

 linder. The pressure 

 of the water in the 

 reservoir, will force 

 water through the 

 piston-valve, until 

 the water rises in the cylinder to the valve 

 V, or to about the level of the water in 

 the reservoir. It would rise to the exact 

 level, but for the weights of the valves. 

 Upon elevating the piston P, the water 

 not being permitted to pass through the 

 piston-valve will be pressed against the 

 valve V, and opening it, will pass into 

 the upper chamber V A of the cylinder ; 

 from whence it is not allowed to return, 

 since the valve V opens upwards. As 

 the piston rises in B V, the pressure of 

 the water in the reservoir forces water 

 after it into the cylinder ; and upon its 

 descent, this water passes through the 

 piston-valve. The next ascent forces 

 water again through V ; and so on. 



The water thus continually forced 

 through V, every ascent of the piston 



