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Oberdorfer™ centrifugal pumps have a single rotating metal impeller. Liquid enters at the center and is thrown outward radically by centrifugal force. The impeller is not in contact with other pump parts resulting in quiet, efficient, pumping action. The flow produced is not positive which permits the discharge line to be shut off completely without danger of overloading motors or bursting lines. Consequently a relief valve is not required. The liquid flow is proportional to the pump speed-the higher the speed the greater the flow. Horsepower required varies directly as flow and pressure. Maximum horsepower is required with a wide-open discharge line. This is the point of maximum flow. With a throttled discharge, the flow decreases at a greater rate than the pressure increases thereby requiring less horsepower at the higher pressures. This is known as an “unloading” feature of the pump. The 50P centrifugal pump has an external ball bearing isolated from the liquid being pumped. The ball bearing is greased and sealed for life, requiring no maintenance.
The pedestal centrifugal pumps can be direct driven by electric motors at either 3450 R.P.M. or 1725 R.P.M. Performance for both speeds are shown in the curves above. The 50P pedestal centrifugal pump can be pulley driven at any desired intermediate speed.
Because centrifugal pumps are more efficient at higher shaft speeds, pumping of viscous or thick liquids is difficult. It is possible to lose as much as 40% pump performance when attempting to pump liquids of viscosity equal to S.A.E. 30 oil at room temperature. SAE 30 oil at room temperature has a viscosity of 2000 Saybolt Seconds Universal. More viscous liquids are not recommended for centrifugal pumps. Heavy liquids can be pumped; however, they demand more horsepower in direct ratio to the weight of water. For example, carbon tetrachloride has a specific gravity of 1.6 which means it is 1.6 times heavier than water and the horsepower required is 1.6 times water horsepower.
This centrifugal pump is not self-priming. Normally these pumps must be installed below the liquid level so that the liquid flows to the pump by gravity. However, if a foot valve is used at the beginning of the suction line and all air is bled from the suction line and pump by careful manual priming, these pumps will lift liquid on the suction side up to 15 ft. Such a system is only as positive as the ability of the foot valve to seal and keep the suction line and pump full of liquid. If the foot valve should leak, the pump will not prime.
Mechanical Shaft Seals have Nitrile rubber components (212°F max) as standard. For temperatures up to 400°F a fluoroelastomer seal must be selected by adding code S10 to the pump number. In most instances, fluoroelastomer seals are not field interchangeable with the standard Nitrile seals. Call factory for details.