While there are undoubtedly a larger num ber of pumps worked by hand than by any other power, such pumps are relatively small, and are not operated continuously. By far the greater tart of the world's pumping, as to volume, is done with what are called power pumps, many of them being very large. The power generally employed is steami although Compressed air is coming more and more into use, being found more economical. (See PUMPS, COMPRESSED-AIR). The attAnlImeni of the power to the pump • has generally taken the tandem form, with the power cylinder at one end and the pump cylinder at the other, the piston rod of the steam cylinder being ex tended to form the piston rod or plunger rod of the pump. This type is known as the direct-acting pump. In other arrangements the steam cylinder may act upon a walking-beam to which the pump rod is connected; or it may work upon a shaft on which is a fly-wheel. Frequently the work is divided, two or three cylinders being provided for both steam and pumps, working alternately or in succession, and thus discharging a more nearly continuous and uniform volume of water. All of these power pumps discharge the water against a longitudinal axis placed eccentrically as to the plunger, but in the centre of a larger cylinder in which the plunger revolves. A longitudinal backstop, actuated by springs, or by its own weight, prevents the water crowded out of one half of the cylinder from flowing back into the half whence it was forced by the plunger. Another form of rotary pump is the pump, a cylinder having a longitudinal centre shaft set with a series of blades like those of, a screw propeller. This is sometimes called an ((impellers pump, and is of great utility in pumping sewage and similar heavy and hetero geneous liquid mixtures which could not be Moved by the forms of primps commonly in use. One of the last-named type was constructed at Milwaukee in 1889 to flush the Milwaukee River of its sewage-polluted waters. It has a screw wheel 13 feet in diameter, which, revolv ing at a rate of 60 revolutions per minute, de livers 550,000,000 gallons of water a day on a lift of four feet. This water is forced through a brick-lined tunnel 12 feet in diameter, and 2,500 feet long. A' battery of 11 of these screw pumps are in use in New Orleans for discharging storm water from the city's drain age system. They are 12 feet in diameter and run at a speed of 75 revolutions per minute. The screw is placed at the summit of a flat topped siphon and is operated by an electric motor. The discharge is about 550 cubic feet per minute, the height raised varying from five to nine feet. The efficiency of these pumps as shown by actual tests is 80 per cent.
The is the best known representative of the type. It em bodies the principle — that a body revolving around a centre tends to move away from it with a force proportional to its velocity; thus be rim of a revolving wheel imparts a portion of its velocity to any substance adhering to it, and throws it off when the force of the velocity thus imparted exceeds the force of adhesion, as the mud thrown off by the wheels of a car riage, or the water from a mop or towel, rapidly revolved by the hand. The first pump of this type was invented by M. Le Demour, who sent a description of it to the Academie Francaise iri 1732. It consisted of a straight tube attached in an inclined position to a vertical axis, around whibh it was whirled by a crank-handle. Later
forms were constructed by tubes joined in the form of a T, the vertical tube of which was placed in the water. The lower end perforated to admit the water, and fitted with a valve to retain the water in The vertical tube when the pump was not in operation, was placed under the surface of the water and supported upon a pivot. The ends of the horizontal discharge tube were bent down into a circular trough over which they were revolved. When the machine was revolved rapidly the centrifugal force which discharged the water in the horizontal tube was communicated to the water in the ver tical, which was also drawn out, hut in the meantime refilled by the atmospheric pressure on the reservoir. When it is required to lift large quantities of water to a low elevation, centrifugal pumps may be used with greater efficiency than reciprocating pumps, the effi ciency of which diminishes with the lift. A pump of this kind, constructed in Massachusetts in 1818; was equipped with four blades set at right angles like those of a fan blower, and was used for many years. An improved form was exhibited by Appold in England, in 1851, which embodied all of the principal features employed in the best pumps constructed since that time. It is stated that Appold's pump raised continu ously a quantity of water equal to 1,400 times its own capacity per minute. The chamber,o designed to utilize the energy de veloped by the whirling water which in most pumps of this type is lost as eddies in the dis charge pipe, was suggested by Thomson (Eng.), and consisted of a chamber somewhat larger than the pump, in which the water discharged by the pump disc, with considerable velocity, was allowed to rotate and impart its energy as an auxiliary aid to the driving power. A pump constructed by him for drainage purposes, in the Barbados, was equipped with a whirlpool chamber 32 feet in diameter, around a pump disc 16 feet in diameter. Others of large were constructed by Easton and Anderson, for the North Sea Canal, in Holland, which were capable of delivering 670 tons of water per minute to as height of five feet; while the Gwynne pumps employed to drain •the Ferrarese tharshes in Italy, at the junction of the Po Volano and the minor rivers of lower Lom bardy, are capable of a combined delivery 2,000 tons of water per minute.
A large class' of pumps, involving the ptin ciple of centrifugal action in some degree are the turbine pumps.
The turbine pump is practically a reversal of the turbine water-wheel (q.v.), being a tur bine run by power, .generally steam, to produce motion or pressure in a body of water or other liquid. It differs from the centrifugal pump in adding the power advantage of the screw to that of centrifugal force. A common applica, don of _this num , uthere th˘ Jjft_ high and the heavy is to place these pumps in series, the second taking its supply water from the first, and so starting its work with a considerable degree of pressure; the third pump taking water from the second, and so on. As many as 10 of these turbines may be thus combined to form the aten-stageD tur bine pump. By this means the load is dis tributed, the velocities of the rotors being trans muted into pressure in the diffusing chambers. These multi-stage turbine pumps are used in the equipment of fire-boats, which are required to deliver great volumes of water at high pres sure.