4. Description of an Improved _Wang Pump.
This pump, shown in Plate CCCCLXX. Fig. S. is a sucking pump, converted by a slight addition into a lifting pump, and fitted for propelling water with any velocity and to any required distance. Near the top of the work ing barrel ABCD of a sucking pump, is joined the pipe Fef, terminating in a rising main ef GH. The top of the barrel AB is terminated with a strong plate AB 771 n, and a stuffing box AB, through which the polished piston rod a b works air-tight, like the piston rod of a steam-engine, so as to prevent either the escape of air or water. The piston cd, which is hollow, has a valve y opening upwards ; and there is a similar valve v at the lower end CD of the bar rel, and there may be advantageously placed a valve x at the bottom of of the main, though it is not necessary.
Let the piston cd be now supposed to be down near v. When it is drawn up it pushes up the air above it, (which will keep down the valve y) driving it through the valve vg in the main where it escapes. The air between cd and v will now expand into the upper part of the barrel below the piston, and it will be rarefied to such a degree, that the predominating pressure of the atmosphere upon the water below will raise it in the suction pipe. When the piston again descends, the air displaced into the barrel from the suction pipe by the ascending water, will get through the valve y, and, upon again drawing up the piston, this air will be driven off and escape through the rising pipe as before. The water is at last brought into the working barrel by repeated •strokes. It gets through the valve y when the piston is down, and when the piston is drawn up the water is drawn up along with it, and lotted up the rising pipe through the valve x.
The advantages of this pump are, 1. That the rarefac tion can be made very complete by bringing the piston near the bottom of the working barrel; 2. That the piston rod being pulled in place of pushed, is less liable to be bent 3. That the parts of the pump are more accessible for repairs; and, 4. That while by putting a cock at z, water may be obtained for common purposes; the pump, by merely shutting this cock, may be used also for extin guishing fire, or for conveying the water to distant places.
5. Description of the Forcing Pump with a Solid Plunger.
This pump, shown in Plate CCCCLXX. Fig. 9. differs from the common forcing pump only in the substitution of a solid plunger ab in place of a piston of the usual form.
This plunger is turned truly cylindrical, and polished, and its diameter is a little less than that of the inside of the barrel. It slides through a collar of leathers AB, which Dr. Robison has described in the following manner: "The top of the barrel terminates in a Ilanch AB, pierced with four holes for receiving screw bolts. There are two rings of metal of the same diameter, and having holes corres ponding to those in the flanch. Four rings of soft leather of the same size, and similarly pierced with holes, are well soaked in a mixture of oil, tallow, and a little rosin. Two of these leather rings are laid on the pump flanch, and one of the metal rings above them. The plunger is then ,thrust down through them, by which it turns the inner edges downwards. The other two rings are then slipped on at the top of the plunger, and the second metal ring is put over them, and then the whole are slid clown to the metal ring. By this the inner edges of the last metal rings arc turned upwards. The three metal rings are now forced together by the screwed bolts, and then the leathern rings are strongly compressed between them, and made to grasp the plunger so closely that no pressure can force the water through them. The upper metal ring just allows the plunger to pass through it, but without any play, so that the turned up edges of the leathern rings do not come up between the plunger and the upper metal ring, but are lodged in a little conical taper, which is given to the inner edge of the upper plate, its hole being wider below than above. It is on this trifling circumstance that the great tightness of the collar depends. To prevent the leathers from shrinking by drought, there is usually a little cistern formed round the bead of the pump and kept full of water."' The operation of this pump is almost exactly the same as that of the forcing pump. When the bottom b of the plunger is in contact with v, it nearly fills the barrel. By drawing it up, a vacuum is made in the barrel. The valve x is shut by the pressure of the atmosphere above, and the air below CD rushes through the valve v into the barrel. and is followed by the water which rises in the suction pipe. The same operation being repeated, the water rises still higher in the suction pipe, till it conies into the barrel. When the plunger ab now descends in the barrel, it will drive the water up into the main pipe through the valve x.