Greenhouses, their construction and equipment . Fig, 120.—Pumping jack for applying power to a hand pump 228 GREENHOUSES COMPFESSEiDAIR iVSll. CAS/A/a electric motor. Usually, a hand pump oflarge size is used, and power is applied bymeans of a pumping jack. A very efficient but somewhat delicatepumping device is the combined hot-air-engine and pumps givevery good satisfac-tion where the wateris reasonably closeto the surface, orwhen it does nothave to be pumpedagainst too great apressure. Improvedtypes of large sizeare now available,and are very econ-omical of fuel, butthe engine is
Greenhouses, their construction and equipment . Fig, 120.—Pumping jack for applying power to a hand pump 228 GREENHOUSES COMPFESSEiDAIR iVSll. CAS/A/a electric motor. Usually, a hand pump oflarge size is used, and power is applied bymeans of a pumping jack. A very efficient but somewhat delicatepumping device is the combined hot-air-engine and pumps givevery good satisfac-tion where the wateris reasonably closeto the surface, orwhen it does nothave to be pumpedagainst too great apressure. Improvedtypes of large sizeare now available,and are very econ-omical of fuel, butthe engine is not aswell adapted forgeneral power pur-poses as are gas en-gines. A form of pump, which is becoming quitepopular for domestic use is the auto-pneu-matic pump. It is designed to be used inan open well or a cased well of large bore,as the pump proper is placed entirely be-. OTO - PNSUMA r/CPUMP Fig. 121.—Diagram showinginstallation of an auto-pneumatic pump IRRIGATION 229 neath the water. It is operated by com-pressed air, hence an air pump and an airtank are required. Its chief advantage fordomestic purposes lies in the fact that itstarts automatically when the faucet isopened, thus giving a supply of cold waterdirect the well. For greenhouse pur-poses this is a disadvantage, as the water maybe too cold to use on the plants. Pump cylinders should not be more than20 feet above the surface of the water, as thisis the limit of practical suction. When thewater is more than 20 feet below the surfacethe pumping cylinders are lowered accord-ingly. In deep wells it is common to lowerthe pumping cylinders well into the water. Capacity of Pumps.—The capacity of apump depends upon the size of the cylinderand the length and rapidity of the table on page 230 gives the discharge perstroke in gallons, of pumps having cylindersof various sizes. Th
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