Best efficiency point ,

Fig. 2. Head—capacity curve, where A represents the minimum allowable capacity B, the best efficiency point (BEP) and C, the maximum allowable...

According to HI convention, for double-suction pumps, Q is half of the total pump flow, ie, taken per impeller eye. The value of S is calculated at the best efficiency point (BEP) at maximum impeller diameter. 

Low Flow Operation. The optimum operation of a pump is near the best efficiency point. Some manufacturers curves indicate the minimum allowable continuous stable flow (MCSF) limits for every pump (43). In the 1980s, the processing industry experienced a reduction in flow requirement as a result of business downturn and installation capacity downsizing. The pumping equipment, however, was generally not replaced by smaller pumps, but was forced to operate at reduced flow rates, often below allowable MCSF. This has resulted in increased failure rates and reduced pump component life. 

Since the exacd value of the hydraulic efficiency e, is never known, V/ can be taken as an approximation where e is the gross (hydraulic horsepower/brake horsepower) pump efficiency. Efficiencies of pump designs running as turbines are usually 5 to 10 efficiency points lower than those as pumps at the best efficiency point. 

The pump manufacturers publish the NPSHr values on their pump curves. We re saying that the NPSH reading is one of the components of your pump curves. Wc ll. see this in Chapter 7 on Pump Curves. If you want to know the NPSHr of your pump, the easiest method is to read it on your pump curve. It s a number that changes normally with a change in flow. When the NPSHr is mentioned in pump literature, it is normally the value at the best efficiency point. Then, you ll be interested in knowing exactly where your pump is operating on its curve. 

Wliere N = the speed of the pump/motor in revolutions per minute Q = the square root of the flow in gallons per minute at the Best Efficiency Point BEP. For double suction pumps, use A BEP Flow. NPSHr = the net positive suction head required by the pump at the BFiP. 

Some pumps are operated at or close to their best efficiency points. Other pumps must run far to the left or right of their best efficiency... 

Ixt .s talk about the pump efficiency. Imagine a small pump connected to a garden hose squirting a stream of water across the lawn. You could direct the How from the ho.se up into the air at about a 45-degree angle, and the stream would arc upward and attain its best distance of reach from the nozzle or launch point. The stream of water would attain a specific height into the air and a specific distance. The efficiency curve of a pump is seen as the trajectory or arc of a stream of water. When squirted from a hose, the elevation that attains the be.st distance, when plotted onto the pump curve, is called the best efficiency point (RHP). On the pump curve, it is seen as in Figure 7. ... 

You can see in Figure 7-9 that the pump should run at or near zone A , its best efficiency point, the BEP. This is the preferred sweet or happy zone. The pump should be specified and operated in this zone. 

On starting the pump and motor, the operators control the service of the mechanical seal. The operators and the process engineers have a tremendous influence on the optimal life of the mechanical seal, just as the operator of a car has the most influence over the optimal life of his automobile. The pump must be operated at, or close to it s best efficiency point (BEP) on the pump curve. 

Although the pump was being run at 25% of the BEP (Best Efficiency Point), it was designed for this type of service. This eliminated improper operation or running outside of the Sweet Zone. 

The values are averaged from tests of conventional single-stage pumps, 2-inch to 8-inch, with capacity at best efficiency point of less than 100 GPM on water performance. 

Figure 3-57. Viscosity performance correction chart for small centrifugal pumps with capacity at best efficiency point of less than 100 GPM (water performance). Note Do not extrapolate. For small 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.)...

Qni = Flead at best efficiency point on pump curve, ft = Viscous liquid capacitv, GPM Q = Water capacity, GPM S =. Suction static head, ft, or height of liquid (static) above ( + ) or below ( —) the center line of the pump on suction side, ft, or,... 

This is based on the flow and specific energy produced by the pump at its best efficiency point of performance following the approach stated by Wisclicenus Any fixed value of the specific speed describes a combination of operating conditions that permits similar flow conditions in geometrically similar hydrodynamic machines. ... 

The flow rate, head, and impeller speed at the maximum or best efficiency point (BEP) of the pump characteristic can be used to define a dimensionless group called the specific speed ... 

Best efficiency point (BEP), 21 63 Best (Management) Practices for fertilizers, 11 127 in operation and maintenance,... 

A volute centrifugal pump has the following performance data at the best efficiency point ... 

BEP Abbreviation for best efficiency point the point or capacity at which a pump achieves its highest efficiency. 

The best efficiency point for the furnished impeller shall preferably be between the rated point and the normal point. 

Specific speed is calculated for the pump s performance at best efficiency point with the maximum diameter impeller. Specific speed is expressed mathematically by the following equation ... 

It is a characteristic of process equipment, that the best operation is reached, at neither a very high nor a very low loading. The intermediate equipment load that results in the most efficient operation is called the the best efficiency point. For distillation trays, the incipient flood point corresponds to the best efficiency point. We have correlated this best efficiency point, for valve and sieve trays, as compared to the measured pressure drops in many chemical plant and refinery distillation towers. We have derived the following formula ... 

K = 0.18 to 0.25 tray operation close to its best efficiency point K = 0.35 to 0.40 tray suffering from entrainment—increase in reflux rate, noticeably reduces tray efficiency K = >0.5 tray is in fully developed flood—opening a vent on the overhead vapor line will blow out liquid, with the vapor K = 0.10 to 0.12 tray deck is suffering from low tray efficiency, due to tray deck leaking... 

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