54

In SI units b W = m3/h X m X sp. gr. = 114 X 150 X 0.90 =

376.5 X efficiency 376.5 X 0.315 40

The Hydraulic Institute Standards limit the use of Figure 16 to radial flow centrifugal pumps with open or closed impellers, handling Newtonian liquids within the pump's normal operating range and within the capacity limits indicated on the chart. Failure to heed these limitations may result in misleading expectations of performance with viscous liquids. Tests on vertical turbine-type pumps, for example, which normally have mixed-flow rather than radial-flow impellers, have shown that, although the viscous efficiency predicted from this chart is quite accurate, the viscous head and viscous capacity predictions are substantially above the demonstrable values. In other words, the performance reductions determined from the chart would not be severe enough for that type of pump. For centrifugal pumps that do not fall within the limits of applicability of Figure 16, viscous performance can be accurately established only by testing.

displacement pumps Both rotary and reciprocating pumps are also frequently used for pumping viscous fluids, and some types are well suited for use where viscosities are beyond the limits for centrifugal pumps. In fact, many common designs are suitable only for use with liquids that are at least moderately viscous because they depend on the viscosity to maintain the lubricating and sealing films between various internal parts of the pumps. Most gear pumps and screw pumps are in this category.

As with centrifugal pumps, the performance of displacement pumps may be significantly affected by changes in liquid viscosity, but the nature of these changes may be quite different. At constant speed, changes in viscosity are likely to have little or no effect on pump capacity. Total head, or differential pressure across the pump, would probably increase with increasing viscosity because of higher system resistance. Thus, the brake power required would increase with even though pump efficiency would not suffer nearly so drastically, if at all, as for a centrifugal pump.

The influence of pump design on how performance varies with viscosity is greater in displacement pumps than in centrifugal pumps. Because there are so many designs, it is not practical to attempt to provide a general means of determining their viscous performance here. This should be done only on the basis of information provided by the pump manufacturer.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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