A common suction pump, shown in Fig. 65, is the type generally 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 atmospheric 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 possible.
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.
Fig. 65. Common Type of Suc tion Pump for Short Lifts..
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 constricted spout, giving the familiar steady stream, is due to the action of the air compressed in the chamber.
Double-acting lift and force pumps draw water by suction on both strokes, and actually 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-chamber in these cushions the delivery.
It may be stated here that hot water cannot 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 fulcrum, and with rod guided in perfect alignment; the handle leverage at least 6 to 1; lift pipe not less than 2 inches; rod, hollow, galvanized or wood; cylinder, at least twice the length of stroke, brass-lined, and not larger in diameter than the lift pipe - the whole being such that all valves can be withdrawn through the pipe and standard 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.
Fig. 66. Type of Lift Pump Adapted to Long Lifts..
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 in pounds to pump with them equals the total lift multiplied by the sectional area of the cylinder in inches.
The importance of cylinder diameter will be better understood by comparison. A total lift of 100 feet, with cylinder 2 inches in diameter, gives 135 pounds, which, with the handle leverage at 6 to 1, will be lifted with from 22 to 25 pounds' force according to kind of rod, tightness of stuffing box, size of lift pipe, etc. With the same outfit and conditions, merely substitute a cylinder of 4 inches' diameter, and 540 pounds will then require to be lifted, which, with the same ratio of leverage, calls for over 90 pounds' force on the handle to lift the water. Then, if the lift pipe is materially smaller than the cylinder, the increase in velocity, when the cylinder water enters the lift pipe calls for an additional force that would astonish one. This should make it plain why so many pump standards are wrecked, bolts worn off, holes worn oblong, handles broken, cylinders continually needing new valves, and owners disgusted; it is all due to the lack of proper proportion of parts, and the enormous amount of needless work thus occasioned.
Total lift is the distance from the level of the source pumped from, to the point of discharge. This includes height to elevated tank, if there be one, and the distance from cylinder to water, if the cylinder is above the water; yet many mechanics are inclined to ignore the latter on the ground that the atmosphere lifts the water to the cylinder. It does, in fact; but the power of the vacuum which permits the atmosphere to lift the water, is as great as the weight of water so lifted, and the vacuum itself is produced and maintained by the energy of the person pumping.