Page 200 - Handbook of Energy Engineering Calculations

flow, gal/min; H = total head on the pump, ft of water; e = pump efficiency,
expressed as a decimal. Typical centrifugal pumps have operating efficiencies
ranging from 50 to 80 percent, depending on the pump design and condition
and liquid handled. Assume that this pump has an efficiency of 70 percent.
Then hp = 8.33(2000)/(350)/[(33,000)(0.70)] = 252 hp (187.9 kW). Thus, the

internal-combustion engine must develop at least 252 hp (187.9 kW) to drive
this pump.

2. Select the internal-combustion engine
Since the engine will run continuously, extreme care must be used in its

selection. Refer to a tabulation of engine ratings, such as Table 1. This table
shows that a diesel engine that delivers 275 continuous brake horsepower
(205.2 kW) (the nearest tabulated rating equal to or greater than the required
input) will be rated at 483 bhp (360.3 kW) at 1750 r/min.

The gasoline-engine rating data in Table 1 show that for continuous full
load at a given speed, 80 percent of the tabulated power can be used. Thus, at
1750 r/min, the engine must be rated at 252/0.80 = 315 bhp (234.9 kW). A
450-hp (335.7-kW) unit is the only one shown in Table 1 that would meet the

needs. This is too large; refer to another builder’s rating table to find an
engine rated at 315 to 325 bhp (234.9 to 242.5 kW) at 1750 r/min.

TABLE 1 Internal-Combustion Engine Rating Table

The unsuitable capacity range in the gasoline-engine section of Table 1 is a

typical situation met in selecting equipment. More time is often spent in
finding a suitable unit at an acceptable price than is spent computing the