• A pump exhibited in the international exhibition of 1862, by Messrs. Farcot & Sons, attains this object in a much more simple manner. In it " two equal pistons, with valves affording very large water-ways, work parallel to each other in two pump cylinders. During the successive strokes, the first piston draws in water by its upper surface, and delivers it to the ascending column by causing it to traverse the second piston. In its ascending course. the second piston raises m its turn the column of water by its upper face, while the lower face sucks the water, causing it to traverse the first pis ton." It will be seen from this description that a valve is placed in each piston, that the cylinders communicate at their base, and that the pistons make their strokes sim ultaneously. This pump has yielded all the good results promised by its ingenious construction, and it is adopted in the water-supply of Paris.
In spite of the-great antiquity of the lift and force pump, it is only of late years that improvements have been introduced into its construction capable of rendering it an efficient machine—that is, one which returns in the shape of water raised, a good proportion of the power applied to it. In 1849 Morin found by experiments that the power lost was 55 to 82 per cent—that is to say,_ that of the motive-power, 45 per cent WŁ1.5 yielded in the best and 18 in the worst, giving an average of about 30 per cent. In 1851 the jury, reporting on those exhibited in the great exhibition, say that it is one of our worst machines, considered in a mechanical sense, as a means of producing a given result with the least possible expense of power. In those exhib ited in the international exhibition of 1862, we find a marked improvement. The jury report that "a large number of constructors have sought to give the waterways and valves dimensions which render as small as possible the loss of power by frie• lion. They have also sought to give a continuous movement to the ascending col 1111311 of water, independently of the action of the reservoir of air." 3. The Chain-pump.—This pump is formed in general of plates of wood fastened to an endless iron chain, and moving upward in a rectangular case or box. There was exhibited in the international exhibition of 1862a pump of.this description called "hur ray's chain-pump;" a pump which is very much used on public works, on account of the case of its construction and erection, and its admirable efficiency even at considerable heights. In this pump, the friction is reduced by having only 3 or 4 lifts instead of 20 or 30, as was previously the case. The chains pass under a roller at the foot, and are driven by a small pitch-wheel at the top, over which they are conducted, and which is driven by appropriate gearing. The lifts feather in passing over the wheel to the descending side, and only unfold when brought round to the ascending side; thus the pump is enabled to take off the water with the same dip as other pumps. The pump is
not liable to be choked, as a back turn of the chain immediately releases any substance getting between the lift and the barrel. The speed is variable, in proportion to the duty required. The speed at which the chain is ordinarily worked is from 200 to 300 ft. per minute. The greatest lift yet made by Murray's chain-pump is 60 ft. high; but it is con sidered that 100 tons of water per minute could be raised 100 ft. high. From 10 to 12 ft. apart has been found to be the best pitch for the lifts; putting them nearer, needlessly increases the friction. Experiments made by Mr. T,ovick for the metropolitan board of works, showed that the slip of the lifts which work in the barrel, and are one-eighth of au inch shorter each way than the barrel, averaged 20 per cent of their motion, and that the useful work done averaged 63 per cent of the indicator horse-power of the engine working it.
4. 11w Centrifugal P217721). —These pumps, with reference to those previously described, may be called new, as, though they have been in use in one form or an other for at least a century, their merits were not brought prominently forward till the year 1851, when the great efficiency of the models exhibited by Messrs. Appold, Gwynne, and Bessemer drew general attention to the subject.
The essential parts of this pump are-1. The wheel to which the water is admitted at the axis, and from which it is expelled at the circumference, by the centrifugal force due to the rotatory motion imparted to it in passing through the rapidly revolving wheel; and 2. The casing or box in Which the wheel works, and by which the entering water is separated from that discharged.
Fig. 2 is a section of a centrifugal pump. The water enters the pump by the supply pipes A, A, which lead to the central orifices of the wheel B; it then passes through pas sages formed by the vanes and the side covering-plates of the wheel. In passing through these passages cf the wheel, which is made to revolve by power applied to the shaft E, it acquires a rotatory motion, which still con tinues when it leaves the circumference of the wheel, and enters the circular whirlpool chamber F; so that the interior of the pump may be looked ou as a whirlpool, extending from the axle of the wheel to the circumfer ence of the whirlpool chamber. Into this whirlpool the water is drawn at the central orifice of the wheel, and discharged by a pipe at the circumference of the whirlpool chamber; and the force with which it is dis charged, or the height to which it will rise in the outlet pipe is measured by the centrifugal force of the water revolving in the whirlpool.