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Pumping high viscosity liquids8/14/2023 Figure 1 graphically illustrates this relationship. If you divide w by 33,000, the result is the HP required at that particular point of flow and head. The equation shows us that the amount of work done by a centrifugal pump is directly proportional to the weight of the pumped liquid. The result is the work performed in ft-lb/minute. Here the flow is multiplied by the weight of a gallon of water and then multiplied by the head in feet. The equation below performs this conversion. A good way to understand the impact of liquid weight is to convert flow in GPM and head in feet into units of work. The weight of the liquid does affect the amount of work done by a pump and, therefore, the HP required. As the equation illustrates, that head depends upon the exit velocity of the liquid from the impeller vanes and the effect of gravity it has absolutely nothing to do with the weight of the liquid. When this equation is applied to a centrifugal pump, h becomes the maximum theoretical head that it can produce. The final velocity attained by a falling object is actually the same as the initial velocity required for it to rise to the same height from which it fell. When rearranged, it takes the form of h = v2/2g and predicts the maximum height an object can attain based on its initial velocity. This equation will predict the final velocity some object will attain when falling from some height (ignoring friction of course). The simplest way to prove the validity of this statement is to use the falling body equation: It is all about the velocity that is added by the impeller. One of the beauties of the centrifugal pump is that the head (in feet) and flow it produces has nothing to do with the weight of the liquid. Specific gravity is important when sizing a centrifugal pump because it is indicative of the weight of the fluid, and its weight will have a direct effect on the amount of work performed by the pump. Therefore, the specific gravity of water is 1- regardless of the measurement system. Since specific gravity is the ratio of those densities, the units of measure cancel themselves, and we end up with a dimensionless number that is the same for all systems of measure. The term specific gravity compares the density of some substance to the density of water. In the metric system its density is one gram per cubic centimeter, or 1,000-kg per cubic meter. At 39-deg F (4-deg C), water has a density of 8.34 pounds per gallon or 62.43 pounds per cubic foot. The density of a substance is defined as its mass per unit volume, but here on the earth's surface, we can substitute weight for mass. This month we will explore specific gravity's effect on the performance of a centrifugal pump. But, if you work with other liquids, you have to consider the effect of these properties on those water based, head/capacity curves. Consequently, specific gravity (SG) and viscosity are not factors when sizing them. This delay permits the ball to seat fully before pumping resumes, even in the heaviest liquids, so that pumping accuracy remains high.For many of us, water is the only liquid that flows through our centrifugal pumps. Variable Oil By-pass stroke adjustment allows an adjustable time delay between the end of the suction stroke and the beginning of the discharge stroke. Teflon® diaphragm withstands most chemicals. Variable Oil By-pass stroke adjustment mechanism provides better valve performance than variable linkage designs. Large internal porting with a large, single ball, suction check valve.Ĭapacities to 30 gph (113 lph) at 100 psi (8 kg/cm 2).Įlectric or pneumatic stroke control options and variable speed drives. Neptune high viscosity, flat diaphragm "V-Pumps" are designed to accurately meter viscous fluids up to 5000 cP such as polymers and other thick liquids.
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