Pumps motor efficiency

Large-capacity high-pressure pump/motor efficiency... 

Improved High-Pressure Pump/Motor Efficiency... 

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. 

The electrical power required to drive a compressor (or pump) can be calculated from a knowledge of the motor efficiency ... 

If the maximum flow-rate required is 20,000 kg/h, calculate the pump motor rating (power) needed. Take the pump efficiency as 70 per cent and allow for a pressure drop of 0.5 bar across the control valve and a loss of 10 velocity heads across the orifice. 

A pump efficiency of 80% is obtained from Figure 8-5. This gives a brake horsepower (BHP) of 37.50. A motor efficiency of 89% is obtained from Figure 8-6. The average power per day used by these pumps is ... 

There will be a small loss in motor efficiency, by using an oversized motor. As process operators and engineers, we can ignore this effect. It is good engineering practice to purchase new motors for the maximum-size impeller that can be installed in a pump. 

If a pump efficiency of 60% is assumed, the pump motor should be rated at (275/0.6) = 458 W. A single stage centrifugal pump would be suitable for this duty. 

Assuming that a squirrel-cage electric-motor drive for the pump is selected, the electric-motor efficiency is determined by interpolating between 100 and 1,000 hp (in Table 5.9). An acccurate determination of the motor efficiency re-... 

We might now well inquire for the purpose of purchasing a pump-motor, say, as to what the work would be for a real process, instead of the fictitious reversible process assumed above. First, you would need to know the efficiency of the combined pump and motor so that the actual input from the surroundings (the electric connection) to the system would be known. Second, the friction losses in the pipe, valves, and fittings must be estimated so that... 

Figure 5,10 FLOWTRAN Subroutine for a Pump Block. The dummy arguments of the subroutine are (1) F and B, the feed and effluent stream vectors containing stream flow information (2) the equipment paramenter vector, R, which contains the outlet pressure and (3) the retention vector, R, which contains the flowrate, pressure increase, fluid Hp, pump efficiency, brake Hp, motor efficiency, and electrical power in kilowatts, all of which are to be printed out. From Seader, I. D., W. D. Seider, and A. C. Pauls, Flowtran Simulation An Introduction 3rd ed., CACHE, Austin, TX (1987).

Note that the above power values are for power dissipated by the jet or propeller and do not include motor efficiency and bearing losses for the agitator, or pump efficiency and external pipe friction losses for the jet. The head loss by the recirculating fluid in a jet mixer can be significant proportion of the total fluid head required for mixing. 

The mechanical losses for pumps and motors are calculated based on motor efficiency, which is assumed at 90% for this example. 

These high efficiency motors and bearings suggestapplications as a high accuracy gyroscope or a helium liquefier pump motor [10]. 

Note that this pump will increase the pressure of the influent water by 250 psi over the pump suction pressure. If the suction pressure is 10 psig, the discharge pressure will be 260 psid). The curve also indicates that the net pressure suction head required (NPSHr) to prevent cavitation of the pump is about 3.45 psi (8.0 feet of water). The efficiency of the pump is about 68%, just about the maximum efficiency for this pump. This pump would be quite suitable for use in the specified RO application. However, in the case where the actual pump efficiency was far from the theoretical maximum, another pump would need to selected that would yield higher pump efficiency. Motor efficiencies nm at about 90%. Each pump and motor combination has its own specific pump curve. 

On account of the great frequency of operations required it is not possible to stop the pump motors when the highest water level has been attained in the accumulator instead of changing over to by-pass. Dis-engageable couplings for the gears are not employed either, as the hy-diaulic by-pass devices are more efficient and less expensive. 

The solid lines are based on a 100 per cent component efficiency and the dashed lines are based on a volumetric pump efficiency ranging from 85 per cent at 1000 psi to 75 per cent 3000 psi and motor efficiencies of 60 per cent at 1000 psi and 50 per cent at 3000 psi operating pressure. 

Pump manufacturers have introduced larger capacity pumps that opaute at higher efficiencies. This has given SWRO designers more options with respect to train sizes. Additionally, the energy consumption of these pump/motors designed specifically for SWRO use is lower than was available in the past. 

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