This pump is said by Dr. Robison to have been invented by Sir Samuel Moreland. The advantage consists in the facility with which the 'plunger can be repaired, and the accuracy with which it may he made to work. See Desa guliers' Experimental Philosophy, vol. i. p. 166.
6. Description of a Pump without Friction.
This machine consists of a wooden tube ABCD, Plate CCCCLXX, Fig 10. either square or cylindrical, having a valve v at its lower end. The depth of the water in the pit must be at least equal to the distance of its surface NO from the place of delivery K. A small cistern EADF is placed at the top of the wooden tube, and on a level with K. A tube KHG, with a valve at H, is united to the tube at G. A beam of wood LNI, and of at least the same length as the tube, is suspended by a chain from a working beam, and is loaded with weights at I, exceeding the weight of the column of water displaced. If this beam now descends by its own weight from the position shown in the figure, the water between NI and v must rise all round it in the narrow space between it and the tube A BCD, and when the bottom NI comes to v, the water will have risen to K, in the rising pipe GEM. When the plunger LNI is drawn up again to the first position, as in the figure, the water in the tube will sink again, but that in the rising pipe will remain in consequence of the valve H having closed. When the plunger descends a second time, the water will again rise in the tube to K, and will now flow out at K, and the quantity discharged will be equal to the part of the plunger L'NI below the surface of the pit-water, bating the small quantity between the plunger and the tube, which may be made very small by a good workman.
Dr. Robison observes, that he has seen a machine con sisting of two of these pumps, which was made by an un taught labouring man, which had great power. • The plungers were suspended from the end of a long beam, the upper surface of which was fixed into a well with a hand rail on each side: A man stood on one end till one plunger descended to the bottom of its tube, and he then walked quietly to the other end, the declivity being at first about 25°, but gradually growing less as he advanced. In this way he caused the other plunger to descend, and so on alternately. Dr. Robison informs us, that a very feeble old man, whose weight Was 110 pounds, raised 7 cubic feet of water 11 feet high in a minute, and wrought eight or ten hours every day. A stout young man, he adds, weigh ing nearly 135 pounds, raised 81 cubic feet to the same weight in the same time, and when he was loaded with 30 pounds, he raised 9i to the same height, working ten hours a•day without fatigue. See Robison's ilfechanical Philosophy, vol. ii. p. 671.
. Description of Haskins' Quicksilver Pump without Friction.
This very machine was invented by Mr. Haskins and improved by Desagulicrs, and has been de scribed in great detail in the Philosophical Transactions for 1728, vol. xxxii. p. 5, and also in Dr. Desaguliers' Ex perimental Philosophy, vol. ii. p. 491.
The first experiment which Mr. Haskins made was with an engine which lie erected at the house of Dr. Desagu Tiers about 1720, but in that engine as much mercury was moved every stroke as the water raised, and conse quently the expense of the mercury was very great. Dr. Desaguliers, however, informed him that he might accom plish his object with a very small quantity of both Mr. Haskins and a Mr. William Vreem found out the
construction represented in Plate CCCCLXX, Fig. 11.
In this figure mnop is a cylindrical iron tube, about six feet long, and open above. Another cylindrical tube, ab, close at top, and of a smaller bore, is connected with it at its bottom on. From the main pipe A proceeds a third iron cylinder efgh, which can move up and down between the other two cylinders without touching either of them. In the main pipe AB there is a valve at v and another at x, as near as possible to the pipe efgh. Let us suppose that the two connected cylinders mnop and ab are suspended by chains Cm, Cp, from the end of a working beam, and let mercury be poured in between mnop and ab till it rises to about three•fourths of the height mn. Let us suppose, also, that the lower end of the pipe AB is plunged in the cistern of water, and that the valve v is not more than 33 feet above the surface of the water. Let us now that the chains Cp, Cm, descend, and along with them the cylinders ab, mnop, then the air above a will he rarefied, the valve v will fall, and x will rise, and a portion of water will rise in the suction pipe B, and the pressure of the external air acting on the mercury between the tubes efgh and mnop, will make it descend in that space and rise in the space between efgh and the tube ab. As mercury is about 13 times heavier than water, it will rise 1 inch in that interval for every 13 inches of rise in the water. if the chains and their attached cylinders are now drawn up, the air which formerly came from the pipe B will be prevented from returning by the valve x. The valve v will there fore rise, and the air will escape through it at the pipe A. By a repetition of the operation, the water will rise higher and higher in the suction pipe, and the mercury rise higher and higher in the interval between efgh and ab, till at last the water will flow through x and fill the whole apparatus. When this is done the cylinders have descended about 30 inches. If they are now drawn up, the water in of cannot return through the valve x, and will therefore be forced up through the valve v into the rising pipe A, because in raising the cylinders the force with which they press against the water, presses down the mercury betwen ab and efgh, and causes it to rise between efgh and mnop, till the two mercurial columns are nearly on a level. The continued rise of the cylinders causes the mercury to fall still farther between ab and efgh, and rise still higher in the space be tween efgh and mnop. Hence, in order to balance this inequality of the columns of mercury, the water rises through the valve v till the height of the water in the pipe A is 13 times the difference of the mercurial columns. When the cylinders are again depressed, more water will rise in the suction pipe, and the rise in the cyliriders will drive the water still higher up the pipe A, and the mercury will be higher in the inner than in the outer space. By continuing this action, the water will rise in A till the mercury in the outer space arrives at the top of the cylin der. Dr. Robison remarks, that with the dimensions already mentioned, the machine will raise water about 30 feet in the pipe A above x, which will make the whole height above the pit-water 60 feet. The machine requires to be slowly worked.