Air lift or compressed air pumping plants consist of one or more air lift pumps. The air compressor with receiver and motive power and the necessary piping to deliver the compressed air from the receiver to the pumps. Each pump consists of: (1) The discharge pipe, which is smaller than the well casing and is placed inside of it, extending below the water surface to a depth equal to one and a half or two times the lift measured from the water surface; (2) the air pipe, which is usually inside the discharge pipe, but may, if the well is enough larger than the discharge pipe to so permit, be placed outside and connected at the lower end of the discharge pipe by means of standard fittings or special castings; (3) the foot piece which is a special casting connected to the lower end of the air pipe and so designed to admit the air evenly in small bubbles-there are various designs of patented foot pieces, but there is little difference in their efficiency; (4) the tail piece which forms a slightly enlarged extension of the lower end of the discharge pipe below the foot piece. The air is delivered through the foot piece at pressures varying acording to the lift and the ratio of diameters between air pipe and water pipe, and its expansion and displacement produces the lifting power. The relation between the volume of air supplied and the volume of water pumped for different lifts has been found by experiment to be as follows: Head in feet Ratio Suction Deep Well Pump Cubic feet of air Cubic feet of water 10 20 30 50 100 1.0 1.5 2.0 2.5 3.0 The velocity of water in the discharge pipe, based on the volume of water pumped should not exceed 5 ft. per second in order to keep down friction losses. The compressor may be direct connected to a steam engine or gasoline engine or may be connected by means of belts, gears, etc., to the driving power which may be a steam engine, a gasoline engine or electric motor. The compressed air passes from the air cylinder to the receiver, which is used to store the air and equalize the pressure. From the receiver the air is conducted through pipes to each well. The efficiency of the plant when properly installed as calculated from the ratio of actual water horsepower to the indicated horsepower in the cylinder of the engine is generally between 20 and 30 per cent. Air lifts are best adapted for pumping from several wells not further apart than half a mile and where the wells are sufficiently deep to allow proper submergence. The hydraulic ram works on the principle that a large volume of water falling through a low head will pump a smaller volume of water through a higher head. The ram consists of the valve box and air vessel, the supply or drive pipe which connects the valve box with Hydraulic Ram. the source of supply and the delivery or discharge pipe which connects the air vessel with the point of delivery. The efficiency of the plant is Eqh/QH wher q=volume of discharge water, h=discharge head in feet above ram, Q= volume of drive water, H = drive head in feet. For best results the ratio of the length of drive pipe to the length of drive head should not exceed 2.5; but it is practicable to increase this ratio to 25 and use a drive pipe 1000 ft. long. The delivery head may be anything up to about 250 ft. and the drive head anything above 18 in. The efficiency diminishes as the ratio of delivery to drive head increases. With this ratio as great as 30 to 1 the efficiency will not be over 20 per cent; with a ratio not greater than 4 to 1 the efficiency may be as high as 75 per cent. Hydraulic rams are usually limited to small quantities of water. A notable example of a large plant for irrigation purposes is one installed at Sunnyside, Washington, for the irrigation of 240 acres of land. The plant was installed by the Columbia Steel Works of Portland, Oregon, and consists of eleven 6 in. rams, with a common discharge cylinder emptying into a 10 in. wood stave discharge pipe. The plant is used to irrigate 150 acres under 105 ft. lift and 90 acres under 144 ft. lift. The lifts are measured from rams. The drive head is 38 ft. and the drive water 5 second ft. The plant was furnished under guarantee to deliver .75 second ft. at higher outlet. The cost of plant is as follows: No maintenance except two visits per day to clear weeds out. An efficiency test gave the following results: H=37.6; h=144.1; Q=6.25; q=1.15: ADAPTABILITY OF THE SEVERAL TYPES OF PUMPS FOR SMALL PUMPING PLANTS Where the source of water supply is a stream or surface body of water, the choice is usually between a power pump and a centrifugal pump and will depend largely on the lift and capacity. Power pumps are best adapted to high heads above 75 ft. and to small or moderate volumes of water, usually under 200 gallons per minute. For these conditions the efficiency of a power pump is usually greater than that of a centrifugal pump. For greater volumes the plunger pumps are comparatively expensive and centrifugal pumps are usually preferable unless the lift is excessive. The centrifugal pump has the advantage that it is simple in construction, with no parts to get out of order, and that it is cheaper than a power pump. Where the source of water supply is ground water with the water table in the well at a depth below the surface not much greater or less than the limit of suction lift, so that a deep pit is not unnecessary, then the choice is between a centrifugal pump, a power pump and an air lift pump. The selection between the centrifugal and power pump will depend on a consideration of lift and capacity as explained above. Air lift plants have low efficiency, require a depth of well below the water table equal to about twice the lift measured from the water table and are hardly to be considered in connection with separate small pumping plants. They are best adapted to a large number of wells. (at least six or preferably more) placed close together. An air lift pump can be used advantageously for a well which is too crooked for the other types of pumps. Where the source of water is ground water developed by deep wells with the water table at a large depth below the surface (50 to 200 ft. or more) the choice is between a vertical centrifugal pump in a pit and a deep well pump which eliminates the pit. Deep well pumps are best adapted where the lift is in excess of 100 or 150 ft. and for wells that do not yield more than about 400 gallons per minute. Their efficiency is greater than that of centrifugal pumps, but the cost of repairs and depreciation is greater. The selection should be made only after careful consideration of the first cost of the pump and the annual cost of fuel, operation and maintenance. Where the lift is high, the fuel cost will be considerable and it is good economy not to select the cheapest pump obtainable, but one that is guaranteed for its efficiency. On the other hand, if the pump is to be operated only during a very small portion of the season, it would be poor economy to invest a large capital in a high grade pumping plant to save in fuel cost. METHODS OF DRIVING The driving power is generally either gasoline engine, steam engine, or electric motor. Centrifugal pumps are usually either direct connected (except for varying low heads) or connected by means of belts. gears, or chains. Power pumps are connected by belts or gears. Direct connection is preferable when possible; it is more efficient and eliminates the adjustment of belt or chain necessary with the belt or chain driven pumps. The connection of these pumps and driving power must be such that the pumps will be given the speed or number of revolutions per minute for which they are designed and for which the highest efficiency is obtained. For this reason direct connection can only be used where the driving power and the pump have the same speed. The speed of centrifugal pumps is usually high; so is that of electric motors; and for this reason they can, if properly designed, be direct connected. This is done usually by means of a flexible coupling. Gasoline and steam engines are generally operated at a much lower speed than centrifugal pumps, and are therefore not direct connected unless the engine and pump are specially designed. This is done by some manufacturers. To obtain maximum efficiency with direct connection when the heads are low and subject to wide variation, it is necessary to change the runners of the pump to |