PUMPS A common suction pump, shown in Fig. 65, is the type generaliy used in cisterns or other very short lifts. B is the plunger; C, the bottom valve; and D, the plunger valve. When the plunger is drawn up, a vacuum is formed in the cylinder, and water flows in through C to fill it. When the plunger is forced down, valve D opens and allows the water to flow through the plunger while C remains closed. Water is thus raised by the plunger at each stroke and flows from the spout in an intermittent stream. The atmos pheric limit is indicated in the engraving; but, as before stated, the practical lift is taken at 20 feet or less in pumps having the plunger valve at the ground level. The plunger in this kind of pump is made to trip the bottom valve and drain the pump at will, without a waste-hole or special cock, by merely lifting the handle as high as pos sible.
When the surface of the water is a greater distance below the pump stock than ordinary suction can reach effectively, the cylinder and its working parts must be placed within the limits of lift by suction. This form is termed a lift pump, one type of which is shown in Fig. 66. This particular form is confined to ordinary open shallow wells or deep cisterns. It drains automatically through a waste-hole always open below frost line, located in the stock above the working barrel. There is no limit except the strength of the parts, to which a good lift pump will not bring water if the cylinder is near enough to the water and the pump in good order.
The forcing feature of a pump, making it a lift and force pump, is secured by working the rod of an ordinary lift pump through a stuffing box, and adding an air-chamber to take care of the surplus water pumped on the up-stroke and to expel it while the plunger is being lowered. All the water is pumped on the up-stroke of the plunger, in these pumps; and the expulsion of the surplus through the con stricted spout, giving the familiar steady stream, is dug to the action of the air compressed in the chamber.
Double-acting lift and force pumps draw water by suction on both strokes, and act ually expel it by force into the discharge, the suction and force being alternate in the same cylinder on both sides of a solid plunger. The air-chambcr in these cush
ions the delivery.
It may be stated here that hot water can not be lifted by suction, because the boiling point of water depends upon the pressure on it. Therefore, any endeavor to create a vacuum with a pump results in vapor rising so freely as to prevent accomplishing appreciable results. Warm water can be forced by having the pump below the source, and practically allowing the water to flow into the pump by gravity.
In wells, whether driven, tubular, or open, it is advisable to have the cylinder very near the bottom. The pump standard, for hand use, should be strong, well-made, of 10-inch stroke, with rocking fuicrum, and with rod guided in perfect alignment; the handle age at least 6 to 1; lift pipe not less than 2 inches; rod, hollow, vanized or wood; cylinder, at least twice the length of stroke, lined, and not larger in diameter than the lift pipe—the whole being such that all valves can be withdrawn through the pipe and stanaarci for repair or renewal without disturbing either standard body or pipe. A drain valve to empty standard and pipe below freezing point, is essential. A pump outfit of this character, to deliver water at the ground level, will require at the handle grip, 6 to 8 pounds force on 40-foot, 10 to 12 pounds on 50-foot, and 14 to 16 pounds on 60-foot wells. The lift pipe (above cylinder) should not be plain iron pipe. Polished iron cylinders ought not to be used, even though they are to be always submerged; incrustation will make it difficult to withdraw the cup-leathers—to say nothing of other objections.
The trouble with cylinders of larger diameter than the lift pipe, is the time and expense of withdrawing pipe and standard for repairs; and, of course, the power. to pump with them equals the total lift multi plied by the sectional area of the cylinder in inches.