Figure 14-33.—Diaphragm pump.unseat (and at the same time keeps the discharge ballvalve seated) and to admit liquid to the pump cylinder.On the discharge stroke, the diaphragm is pusheddownward forcing the trapped liquid out through thedischarge valve. Thus the liquid is made to move by thereciprocating motion of a flexible diaphragm.Since the diaphragm forms a tight seal in the pumpcylinder between the liquid being pumped and the restof the pump and driving mechanisms, there is littledanger of liquid abrasion or corrosion of moving partsbehind the diaphragm.NOTE: Diaphragm pumps are especiallywell-suited for pumping mud, slime, silt, and otherwastes or heavy liquids containing debris, such as sticks,stones, or rags.Liquid strainers are fitted at the suction inlet toprevent large objects from fouling the suction anddischarge valves or possibly damaging the diaphragm.You may have to use the diaphragm pump for suchduties as dewatering trenches where sewer lines orwaterlines are to be laid, dewatering cofferdams orcave-ins, or repairing breaks in water or sewage lines.Two of the most popular types of diaphragm pumps arethe mud hog (closed discharge) and the water hog(open discharge).The mud hog is for jobs that require pumping heavyand thick liquids that must be discharged at a distanceaway from the pump. The pump is fitted with dischargehose connctions, and the ball valves and chambers aredesigned to prevent fouling by sticks, stones, or rags.The water hog is used for pumping thinner or lessviscous liquids. It can handle liquids containing sand,gravel, or mud. The discharge outlet from the water hogis open to permit free flow and to increase dischargecapacity. The liquid is discharged directly at the pump.A discharge hose, however, can be fitted to the pump ifdesired, but the hose connection can reduce theefficiency of the pump.You must know the operation of the diaphragmpump. Since nearly every job presents a differentproblem, you may have to vary the operating procedureto fit the individual job.Before starting the pump, place the suction line andscreen in the liquid to be removed by the pump.Construct a trough to drain the pump discharge awayfrom the pump.OPERATION.— Start the engine first. If the pumpdoes not pick up the liquid in a minute or two, check thesuction line for leaks. You can do this by pouring waterover the hose connections. In the event there is a leak,air bubbles will appear.Should the connections be tight and no leaks appear,check the diaphragm for cracks or punctures. If thediaphragm is damaged, it has to be replaced. Amechanic inspector must make any further inspections.INSPECTION.— Because of the nature of theliquids handled by diaphragm pumps, inspection duringpump operation becomes particularly important.Inspect the suction inlet strainer often to avoidaccumulations of debris that reduce suction efficiency.Most diaphragm pump installations also permit easyaccess to the suction and discharge ball check valves.These valve mechanisms should also be inspectedfrequently to detect scoring, fouling, and improper valveseating.NOTE: Sand, gravel, and other material cancorrode the diaphragm and ball check valves; expectthese parts to require the most frequent operatorinspections.Centrifugal PumpThe basic centrifugal pump has only one movingpart: a wheel or impeller that is connected to the driveshaft of a prime mover and that rotates within the pumpcasing. The impeller is designed to impart a whirling orrevolving motion to the liquid in the pump. When theimpeller rotates at relatively high speeds, sufficient14-29
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