PUMPS AND PUMPING MACHIN ERY. In the modern acceptation of the term, a pump is a machine for exerting mechanical action upon fluids. It is commonly employed for raising liquids to a higher level; for propelling them through pipes and orifices under (hydrats• lic) pressure; and for the compressing and rarefying of gaseous substances. The pumps used for compressing gases are discussed under the title Ant COMPRESSORS; those for rarefication under Ant-PUMP and VACUUM-PUMP.
Pumps operate by two quite distinct methods, and are consequently classified as (1) suction or pumps and (2) force pumps. The suction pump depends for its operation upon the constant pressure of the atmosphere-14.7 pounds per square inch. The action of the pump is to release from this pressure that area under the influence of the pump's piston : the air pressure outside of that area causes fluids affected by it to flow into the space in which the pressure has been diminished. In the force pump the force is applied directly by the pump mechanism to the fluid to be moved, regard less of atmospheric pressure. In its simplest form, the modern atmospheric or suction pump consists of a cylinder (c) connected at the bot tom with a pipe (p), the lower end of which is immersed below the surface of the water. In the cylinder are placed two valves (isv and lv), the lower stationary and the upper attached to a piston (f) at the end of a rod (r), which moves the piston up and down under the motion of a handle (h). A pipe or spout (s), attached to the cylinder near its upper end, receives and discharges the water raised by the working of the piston. Both the valves open upward, and the action of the entire arrangement, based upon the physical fact that two bodies cannot occupy the same space at the same time, is as follows: When the downward stroke of the handle moves the piston upward, the air in the space A is rarefied, having to occupy a greater space, and the partial vacuum thus formed re lieves the pressure of the atmosphere from the lower valve, which being opened upward by the pressure of the air in the space (B) of the pipe, allows a portion of it to pass into the space (A). When the piston descends
under the upward stroke of the handle, the air in the space (A) is compressed, the lower valve Is closed, and when the density of the com pressed air becomes greater than that of the atmosphere, the upper yelve is forced open and the air passes into and out of the space (D). Thus, by the continued up and down movement of the piston, all the air in the space (B) is completely exhausted, the water rising in the suction pipe under the pressure of the atmos phere upon its surface in the well, until it fills the space (B) up to the lower valve. The next upward movement of the piston empties the air in the space (A), which is immediately filled with water by the opening of the lower valve. The downward motion of the piston reheves the pressure and allows the lower valve to fall into its seat. The water then in the lower part of the pump flows through the valve in the piston into the space (D), from which it is discharged through the spout by the next up ward movement of the piston which at the same time refills the space (A) by suction. Under the laws of fluid pressure discovered by the ex periments of Torricelli and others, the height to which a column of water will rise depends upon the atmospheric pressure at any point on the earth's surface, and varies with the altitude of that point. At the level of the sea, the atmosphere exerts a pressure of 14.7 pounds to the square inch, and will support a column of water in a closed tube from which the air has been exhausted; ,between 33 and 34 feet in height, while u .n the top of Mont Blanc, or Pike's Peak, 15,111 or 16,000 feet above the sea, the atmospheric pressure will support a similar column of water only abopt 16 or 17 feet in height. A knowledge of this fact is important not only in determining the maximum distance at which the lower valve of a pump may be placed from the surface of water to be pumped, but also in every branch of hydraulic engineer ing in which atmospheric pressure is utilized.