The force-pump barrel is usually set in a horizontal position, with the pump handle ver tical, so that the man pumping can throw his weight against it in much more effective fash ion than in an up-and-down stroke.
A- lift pump is one that raises the water bodily by lifting or scooping it up; it may employ a piston in a tube, but the common de vice is an endless chain with circular buckets fixed a few inches apart, these buckets being shaped like washers and fitting loosely the bore of the pipe through which the chain is raised. The chain is hung at the top over a driving windlass; the lower end dips in the water; the turning of the windlass by a crank draws one side of the chain up through the pipe, and the washer-like buckets draw up the water between them. The old-fashioned ship-pump was the simplest sort of lift pump, consisting of a pipe running from the deck nearly to the bottom of the ship's hold. In this pipe was let down a rod, having a handle at the top and dish-shaped leather buckets near the lower end. By working the handle up and down the sailor who manned the pump lifted water in a con tinuous stream. With such a pump it was nec essary for the sailor to make the downward movement rapidly, so as not to lose the water raised, while reaching down for more.
A centrifugal pump of the form also called a rotary pump is one having a short cylindrical case, in which turns a rotary piston having several radial arms that embrace sectors of the cylindrical space, so that water may be ad mitted at one side and passed out at the other side. Tesla's pump might also be called centrif ugal, since it receives the water axially in a wheel, and throws it out at the periphery; its fundamental characteristic, however, is capillary attraction or skin friction. By placing several discs about three-sixteenths of an inch apart and rotating them in unison the water is picked up by the side friction of the discs, and then when the disc spaces are full, it is thrown out by centrifugal force. A centripetal pump is one having a rotating mechanism that picks up the water at the periphery and delivers it at the axis, a sort of reversed turbine.
Steam pumps are made in numerous forms, some being simple force-pumps operated by a steam-engine. A common direct-acting steam pump has large gears mounted in a water-tight case, and meshing closely so that their rota tion withdraws the air from a water pipe, creates a partial vacuum and raises the water.
The propeller pump, or spiral pump, also called Archimedes pump, employs an inclined tube, within which a broad-bladed screw turns, the edges of the blades filling the tube. When the lower end is placed in water, and the tube placed at an angle of about 30 degrees, rotation of the screw picks up the water by the advancement of the blades and carries it to the top.
The vacuum pump utilizes a closed vessel, to which steam is admitted and a little cold water then turned in to condense the steam. This condensation forms a partial vacuum, and because of atmospheric pressure the water rises and fills the steam chamber. The pulsometpr pump is of this type. It consists essentially of a double chamber, having a ball-valve at to and clack-valves at bottom. Steam is admitted to one of the chambers and presses out the water contained there. Condensation then talc ing place a vacuum is formed, and the ball falls over and closes the opening through which the steam entered and water flows up through the clack-valves and again fills the chamber. The steam in the meantime acts upon the water contained in the adjoining chamber. Conden sation then taking place there, the ball falls back to that side, and the operations go on alternately, the result being a steady stream of water sucked into one chamber after an other, and then forced out and upward by the steam pressure. The water is drawn into the machine from the centre.
A hydraulic or hydrostatic pump is simply the pump of a hydraulic press, crane, punch, etc. The principle of the hydraulic press and hydraulic ram are described under those titles. The hydraulic crane and hydraulic punch are simply a crane or a punching press having one or more hydraulic cylinders with large diam eter pistons which are moved with great force by means of water pumped in through a small aperture. The pressure of water varies with the degree of surface. If a stream of water of one square inch cross section be forced into a large cylinder under a pressure of 100 pounds, the pressure of the water will move a piston of 500 square inches surface sliding in the large cylinder, with a push of 50,000 pounds, less the friction involved, which is slight. The larger piston of course will move at one five-hun dredth of the speed of the smaller pumping piston.