1194

THEORY AND PRACTICE OF ENGINEERING.

Book II.

as each piston forces twice at each turn of the lantern, the three together will make 3636strokes per hour.

The pistons being 2.J inches in diameter, and 8 inches lift, they force at each stroke a columnof water of 39| cube inches, which being multiplied by 3636 gives 142843 cube inches perhour raised to a height of 150 feet: if it be required to raise water higher than 150 feet,the piston must be diminished in superficies, otherwise the power of one horse would notsuffice; if, on the other hand, a less height be required, the superficies of the piston mustbe increased, or the horse would not raise a quantity equal to his mean strength. To pro-portion the pump-barrels in either case, the following rule will be found useful: thediameter of the pistons being 2£ inches, its square will be 6^ inches, which, multiplied by150 feet, gives 937.J, and this may be taken for the weight of a column of water forcedby each piston ; but as the diameter of these pistons might be greater if the pumps were notto a certain extent defective, we may, supposing them to be perfect, take 1000 for the ex-pression of a column of water instead of 937^, and this will still be too low an estimate :this number of feet is then divided by the height the water is to be raised, and the squareroot of the quotient will give the number sought: for example, if the water is to be raised60 feet, 1000-~60 = 16 !*, whose square root is 4^ inches.

The pumps may be placed at any convenient height above the water by using suction-pipes to raise the water from a brook or river ; the number 1000 must then be divided bythe height of .the reservoir above the water, and not by its height above the pumps.

M. de la Hire, in his treatise on Epicycloids, has described a very simple method ofworking pumps, as executed by M. Desargues at the chateau of Beaulieu, eight leaguesfrom Paris .

In fig. 1857., L M () I is a large wheel, placed horizontally, and composed of severalpieces of timber firmly united ; the axle, AB, of this wheel turns on a pivot and socket,and is kept in its place by a timber framework: the wheel has five wavy teeth onits edge, at OI, which act on the rollers that turn on an axle, C; this axle iscarried by an arm, 1)C, also movable on an axle at D; the arm D C is attached to aportion of a circle, DEF, in such a manner that one cannot move without the other.On the thickness of the arc is a double fiat chain, II G, attached at E: this chain has tworings at its extremity, which support the iron stirrup of a forcing-pump. The lever orarm, N, of this ma-chine is let into theaxle at B, and may beattached to the wheelfor greater strength.

There are two rollerssimilar to the onedescribed diametri-cally opposed to eachother under the wheel,and which ought toact alternately ; forwhen one is in thehollow of the wheelthe other is on thewave : but the wheelturning from O to I,the roller will descendfrom the part O Q,and remount on theopposite side. Thepart O Q is alone tobe considered, for itis that which causesthe roller to descend,and raises the pistonof the forcing-pump.

no effort, but only follows the sinuosity of the tooth, being raised by the weight of thepiston as well as that of the triangle DEF, which fall by their own weight. The wholeeffort of the wheel is due to its weight, so that if it be as heavy as the column of watersustained by the piston, it is evident that there will not be any considerable friction on thepivot P ; it must, however, l*e heavier, so as not to be liable to lifting out of its socket,otherwise it will work on both rollers at once: the number of teeth should be unequal,in order that one roller may always work, and the power moving the lever N act equally,and not by jerks.

Fig. 1858

The roller remounting on the other part of the wheel makes