Pumps performance corrections

Example 3-16 Pump Performance Correction For Viscous Liquid... 

FIG. 10-31 Typical pump performance curve. The curve is shown for water at 85 F. If the specific gravity of the fluid is other than unity, BHP must he corrected. 

Figure 3-56. Viscosity performance correction chart for centrifugal pumps. Note do not extrapolate. For centrifugal pumps only, not for axial or mixed flow. NPSH must be adequate. For Newtonian fluids only. For multistage pumps, use head per stage. (By permission. Hydraulic Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps, 13th ed.. Hydraulic Institute, 1975.)...

When a pump performance is defined for water, the corrected performance for a viscous fluid can be developed using Figure 3-56 or 3-57. In order to develop the curves for viscosity conditions of 100 SSU or 1,000 SSU as shown in Figure 3-58, the following general procedure is used [17]. 

Normal fire protection practices and standards recommend fire pumps be tested annually to determine performance levels. Common practice in the petroleum industry is to trend the result of flow performance to prepare predictive maintenance and replacement forecasts. Such forecast can predict poor pump performance and prepare measures to implement corrective actions before this occurs. 

Pumps that handle liquids more viscous than water shall have their water performance corrected in accordance with the Centrifugal Pump Section of the Hydraulic Institute Standards. 

In any vacuum system the operator must ensure that any unwanted lines are isolated and all vacuum points are shut off when not in use. Vacuum is easily lost by relatively small leaks which, of course, are not readily apparent as the leaks are into the pipe or vessel. If the required vacuum is not attained, it is best to first locate the fault by the following procedure Isolate the vacuum pump or ejector and check that the gauge adjacent to the pump or ejector is performing correctly. If this is satisfactory, close all valves in the system and then open up each section in turn working away from the vacuum source. This will reveal the faulty section or sections and will reduce the area of search for leaks. Alternatively, the system may be pressurized and checked for leaks with soapy water as previously described. 

A lot of papers have been published over the years on various aspects of wear in a slurry impeller or volute, performance corrections and derating, etc. The reader of these papers is often left with the impression that the design of these pumps is a combination of science and art. What is often lacking in the literature are guidelines for the design of slurry pumps. 

Menon, E. S. 2005. Piping Calculations Manual. New York McGraw-Hill. Nine chapters cover different types of piping systems water, fire protection, wastewater and stormwater, steam, compressed air, oil, gas, fuel gas, and cryogenic and refrigeration. Appendices cover units and conversions, pipe properties, and viscosity corrected pump performance. 

The large variety of displacement-type flmd-transport devices makes it difficult to list characteristics common to each. However, for most types it is correct to state that (1) they are adaptable to high-pressure operation, (2) the flow rate through the pump is variable (auxiliary damping systems may be employed to reduce the magnitude of pressure pulsation and flow variation), (3) mechanical considerations limit maximum throughputs, and (4) the devices are capable of efficient performance at extremely low-volume throughput rates. 

To correct this condition with an opened impeller, it s nece,s,sary to perform an impeller adjustment to correct the strict tolerance between the blades and the volute. Some back pullout pumps arc designed with jack bolts on the power end of the bearing housing to easily perform this adjustment without pump disassembly. 

I he focus of industrial plant maintenance has always been that the de,sign is correct, and that the operation of the pumps in the. system is as it should be. In this book, you will see that in the majority of occasions, this is not true. Most of us in maintenance spend our valuable time, just changing parts, and in the best of cases, performing preventive maintenance, trying to diminish the time required to change those parts. 

Mdien dscous liquids are handled in centrifugal pumps, the brake horsepower is increased, the head is reduced, and the capacity is reduced as compared to the performance with water. The corrections may be negligible for viscosities in the same order of magnitude as water, but become significant above 10 centistokes (10 centipoise for SpGr = 1.0) for heavy materials. While the calculation m.ethods are accepta oly good, for exact performance charts test must be run using the pump in the service. 

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