PUMP is the name given to a Iva known engine for raising water above its natural level. It was invented by Ctesibius, as we have already stated in our but has received many improvements in modern times. In giving an account of the most import ant variations which this engine has undergone, we shall begin by describing the three forms in which it generally appears, viz. the sucking pump ; the lifting pump ; and the forcing pump.
1. Description of the Sucking Pump The sucking pump is represented in Plate CCCCLXX, Fig. 1. where ABDC is called the barrel, and CDEF the suction pipe, which are joined to one another by flanges at CD, (if they are made of cast iron,) so as to be perfectly air tight. The lower end of the suction pipe is immersed in the water to be raised, and generally has a grating across it to prevent the entrance of extraneous substances. The piston c d, attached to the lower end of the spear or rod a b, is a hollow cylinder, and has its exterior circumference formed of leather, so as to move tightly in the barrel ABC, without permitting any air to pass between it and the barrel.
In the centre of the piston there is placed a valve v opening upwards, and at CD another x of the same kind, the construction of which is shown in Figs. 2. and 3. In Fig. S. CD corresponds with CD in Fig. 1, and 1, 2, 3, 4, are the screw holes of the flanges. Upon this plate, with a part NL cut out, there is applied a ring of thick leather NKL ; and another piece of strong leather NR, composing the valve, has its end N placed in the opening NL. The circular part of the leather or valve NR, is of a greater diameter than the opening in the leather NKL, but is not so great as to fill up the circle GK[, Fig. 3. Two brass plates, the uppermost of which is seen at R, are used to strengthen this valve, the under one being a little smaller than the apeiaure in the valve plate, and the upper one a little larger than that aperture.
When this plate is inserted at CD, the tail of the leather valve at N will be compressed between the plates, and will become a hinge on which the valve can rise or fall. A
valve nearly similar is placed at v.
The operation of the pump will now be readily under stood. When the piston c d is depressed towards CD by the power of a man working at the rod or spear a b, the air between c d and CD forces up the valve v, and occupies the space passed through by the piston c d; but, upon drawing up the .piston towards AB, the pressure of the air above c d shuts the valve, and consequently all the air in the barrel below c d, and in the suction pipe, is rarefied. The atmospheric air being no longer balanced by that in the pipe, the equilibrium can only be restored by the water at the bottom of the auction pipe rising a little in that pipe. By depressing the piston a second time, and again drawing it up, the air below c d is again rarefied, and the water rises a little higher in the suction pipe, till, by successive strokes of the piston, the water rises through the valve, and pressing the valve down by its weight remains there. If the piston is now made to descend in the water above CD, it will rise through the valve v, and will be lifted up by raising the piston into the reservoir MN, from which it may be conveyed by a spout or pipe for user Hence it is obvious, that whenever the piston c d is raised, the valve x will rise, and the valve v fall, and vice versa. As the whole pressure of the atmo sphere is equal to about a column of water of 32 feet, the perpendicular height of the piston cd above the surface of the water in the well must never exceed 32 feet.
2. Description of the Lifting Pump.
The lifting pump, which, properly speaking, is only the sucking pump inverted, is shown in Fig. 4. Plate CCCCLXX. In this pump, the spear or rod of the pump consists of a frame a in b, a n b, to which is fixed the piston c d, with its valve v opening upwards. At the flange CD there is also another valve x opening upwards.