It with be proper to connect these hoops, before putting them in, by three or four cords, from top to bottom, which will keep them at their proper distances; thus will the bag have the form of a barber's bellows or powder-puff. The distance between the hoops should be about twice the breadth of the rim of the wooden ring to which the upper valve and piston-rod are fixed. Now let this trunk be immersed in the water. It is evident, that if the bag be stretched from the compressed form which its own weight will give it by drawing up the piston-rod, its capacity will be enlarged; the top valve will be shut by its own weight; the air in the bag will be rarefied, and the atmosphere will press the water into the bags. When the rod is thrust down again, this water will come out by the top valve and fill part of the trunk. A repetition of the operation will have a similar effect; the trunk will be filled, and the water will be discharged by the spout.
Many attempts have been made to introduce pumps worked by a continuous rotary motion, and a great deal of ingenuity has been exercised to prevent that waste of power arising from friction, with which they have all been more or less accompanied, but in a greater degree than the best reciprocating pumps. The reader who is solicitous for information on this point will find numerous descriptions of patented inventions of the kind in the Repertory, the London Journal, the Register of Arts, etc.; but as none of them have, in our opinion, been yet brought to work so well as the reciprocating pump, we shall here add only one of those contrivances, which possesses as strong claims to notice as any of them. It was the subject of a patent granted to Mr. Robert Winch, of Battersea, in 1826, and is delineated in the subjoined cut, which represents a vertical section. At a a is a cylindrical case of metal, the holes at the circumference being for the bolts, by which the circular side-plates are secured to it; b is the rising main pipe from the well; kkk the waterway, and c the discharge pipe; d is a circular box, turned round upon the hexagonal shaft in the centre by a winch outside.
To the periphery of this circular box the flap-pistons g g g g are fixed by joints, and, as they revolve, they are successively closed as they come in contact with a "circular inclined plane" ee,the under side of which forms a stop to the upward course of the water on that side of the cylinder. On passing the curved piece e, the pistons successively fall open, with their edges touching the interior surface of the pump case; the water which has passed up from the main pipe through the valves i i, and occupied the spaces marked kk, is then carried forward by the pistons as they revolve, and is discharged in a continuous uniform stream at c. To prevent the pistons from striking violently against the cylinder,. as they are turned against it by the resistance of the water, as well as to avoid hard rubbing in those parts, catch-hooks hhhh are employed, the action of which is too obvious in the drawing to require more explanation
To facilitate the shutting of the flap-pistons, as they come in contact with the curved piece e, each of them have a second joint in the middle, which gives them great flexibility of motion. In another modification of this invention, the patentee employs a rotary vane for closing the flap-pistons or valves in succession, instead of the curved stop described; but this arrangement renders it necessary to have a toothed wheel fixed to the axis of the circular box, to work a pinion on the axis of the rotary vane, that the motion of the latter may exactly correspond with that of the pistons. Since it is impossible, when a pump is well made and is in good order, that the piston can move without displacing the water that is above or below it, according to the circumstances of its construction, so, in all pumps that consist of cylindrical working-barrels and pistons, nothing more is necessary to ascertain the quantity of water they will deliver, than to calculate the solid or cubical contents of that part of the barrel in which the vacuum is produced, and to reduce it to some standard measure, and then to multiply this by the number of strokes made in a given time: thus, if a pump is nine inches diameter, and makes an effective stroke of about eighteen inches, such a cylinder will be found to contain 1134 cubic inches; and as 277 1/4 cubic inches make an imperial gallon, so four gallons will be equal to 1109 cubic inches; consequently, such a barrel will contain and throw out rather more than four gallons at every stroke; and supposing this pump to make ten strokes in a minute, it would yield above forty gallons in a minute, or sixty times that quantity in an hour, and so on.
This rule applies in every case, whether the water is sent to a small or great elevation, because the piston cannot move without displacing the water in the barrel; but a small allowance must be made for leakage, or waste, because some water will.constantly pass the piston and escape, or be otherwise lost and wasted.