Page:The New International Encyclopædia 1st ed. v. 16.djvu/619

* PUMPS AND PUMPING. 541 PUMPS AND PUMPING. PUMPS AND PUMPING MACHINERY (OF., l-"r. pompc, Ger. Fuinpc, Plitmpe, Plumpfe; possibly, though very doubttully, connected with Lat. plumliuin. lead). Devices used to move liquids and gases. The various kinds of pumps, without regard to their motive power, may be broadly classified as follow s : ( 1 ) Bucket lifts, or water elevators, by means of which a balanced pole, or sweep, a windlass, or a wheel, lowers, raises, and empties one or more buckets or other receptacles. (2) Displacement pumps, acting on the principle that two bodies cannot occupy the same space at the same time. (3) Impellers, which by their own continuous motion in the wa- ter to be moved impart some of their velocity to water with which they come in contact. (4) Im- pulse pumps, which employ the force of a sud- denly arrested large column of water to lift a smaller column to a greater elevation than the original source. See Htdraulic Ram. Bucket Litt-s, or Water Elevators. These are the simplest of the four classes of pumps named. They have been used from the remotest historical times and are still employed in vary- ing forms the world over. The well sweep, or bucket and balanced pole, still frequently seen in certain rural sections of America, is much the same as the shadoof of Eg^pt and the paecottah of India. The single bucket or. in Oriental countries, the earthen pot attaclied to a rope wound around a windlass, is another very com- mon water lift. A series of buckets mounted on an endless rope or chain, dipping into the water below, and running over ami driven by a wheel above, is an improvement over either of the fore- going, giving a continuous stream of water. Primitive multiple bucket or pot lifts of this gen- eral character, driven by animal power acting through a rude combination of wheels and hori- zontal sweeps, are sometimes known as Persian wheels, ilodern refinements of this device are called chfiin pumps. .Sometimes the wheel carry- ing the buckets is placed in and driven by a running stream. Another form of water lift is the scoop wheel, composed of a series of curved blades, terminating in a hollow axle, into which they discharge the water scooped up by the revo- lution of the wheel. Where similarly arranged curved tubes take the place of the blades the de- vice is called a tttmpanum. Of the various water lifts described the bucket and chain pumps are most extensively used, particularly where manual labor is costly. Displacement Pumps. In their most com- mon form they employ a piston to push water ahead of them in a cylinder which the piston tightly fits, or else a plunger which does not wholly fill the cylinder, instead of forcing all the water in the cylinder ahead of it, merely dis- places a volume equal to that of the plunger itself. Instead of a piston, steam or air may be used to effect the displacement. Valves are an essential feature of displacement pumps, and may also be used on the outlet end of impeller or centrifugal and jet pumps, to prevent back pres- sure when the pumps are not running. In the simplest form, as in the ordinary suction lift pump, described below, valves are nothing more than pieces of leather or rubber, cut to the de- sired shape, and hinged at one edge or side. They lift for the passage of the water upward and close on the reverse stroke of the piston in order to prevent a reverse flow. In most large pumps many small valves are employed, instead of one of sufficient size to accommodate the w hole flow of water. This reduces the shock and jar due to the sudden opening and closing of the valves. The majority of such valves consist of an inlet, valve seat, disk, or valve proper, stem, cover plate, and spring, although the spring may be omitted. The disks are commonly made of vulcanized india- rubber, and the other parts of bronze. Ball and cone valves are also used, particularly on deep ■ Outlet Val ye -Outlet Valves ■-Inlet Vahes-' Double = Aci-ing Piston Pump. Outlet Single-AcHng Plunger Pump. Outlet Inlet Centrifugal Pump. Air Li-fr Pump. PUMPIXG MACBINEEY — TYPES OF PUMPS. well pumps. The Reidler valve, a German device used on some of the highest grades of American and foreign pumps, employs only one valve on each inlet or outlet, which is closed mechanically, instead of by the force of the liquid being pumped, and therefore has a positive and comparatively gentle motion, combined with a single large water- way of ample capacity. Valve stems control the lift of the valves and prevent displacement from their seats, while the springs are designed to take up slacks. When the only function of a valve is to prevent back pressure, or flow, a single check or flap valve may be used. Displacement pumps are subdivided into many classes, of which the following are the most im- portant: Reeiproeatinr/ pumps have either pis- tons or plungers which move alternately b.ick and forth or up and down, always in a straight line. Such pumps are single or double acting, accord-' ing to whether the water is displaced on one or both parts of the stroke. They are also known as direct-ttcting when the motive power is applied in a direct line with the movement of the piston or plunger, and as of the crank-and-fty-irheel type, or the beam type, when either of these de- vices is employed to transmit the motion. The beam is similar to the walking-beam of some steamboats and is an essential feature of the old Cornish beam engine. (See Steam Engines.) Pumps are knowni as simple, duplex, triple, etc., according as one. two. or more pistons or plungers are driven by a motive power unit. Beam pumps are rapidly diminishing in relative numbers. Crank-and-fly-wheel pumps are quite extensively used, particularly for high duties and for power pumps. Directacting pumps are very common. Wliile large numbers of simple pumos are in use. duplex and triple, but more particularly du-