| TABLE 31 | |||
|---|---|---|---|
| Costs of Complete Pumping Stations | |||
| These costs include the best type of triple-expansion engines, high-pressure boilers, brick or inexpensive stone building with slate roof, chimney and intake. Cost of land is not included. | |||
| Discharge Pressure, Lbs. per Sq. In. | Horse-power per Million Gals. Pumped | Cost, Dollars per Horse-power | Cost, Dollars per Million Gallons |
| 30 | 12 | 562 | 6,750 |
| 40 | 16 | 438 | 7,000 |
| 50 | 20 | 362 | 7,250 |
| 60 | 24 | 312 | 7,500 |
| 70 | 28 | 277 | 7,750 |
| 80 | 32 | 250 | 8,000 |
| 90 | 36 | 229 | 8,250 |
| 100 | 40 | 213 | 8,500 |
| 110 | 44 | 200 | 8,750 |
| 120 | 48 | 187 | 9,000 |
| 130 | 52 | 192 | 10,000 |
88. Cost Comparisons of Different Designs.—In the design of a pumping station and its equipment the relative costs of different designs should be compared, and the least expensive design selected, due consideration being given to serviceability, reliability, and other factors without definite financial value. In comparing the costs of different types of machinery, all items in connection with the pumping station should be considered. For example, the cost of an electrically driven centrifugal pump and equipment may be less than the total cost of a steam driven reciprocating pump and equipment because of the saving in the cost of boilers, boiler house, etc., but a comparison of the capitalized cost of the two might show in favor of the reciprocating steam pump because of the lower cost of operation.
The total cost of a plant, or any portion thereof, may be considered as made up of three parts: (1) The first cost, (2) operation and maintenance and, (3) renewal. The total cost S can be expressed as
S = C + O
r + R,
in which C = the first cost; O = the annual expenditure for operation and maintenance; R = the amount set aside to cover renewal; r = the rate of interest.
S is called the capitalized cost of a plant. The annual payment necessary to perpetuate a plant is
A = Sr = Cr + O + Rr.
The value of R is useful when expressed in terms of the life of the plant or machine and the current rate of interest. It is sometimes called the depreciation factor or capitalized depreciation. If it is borne in mind that R is the amount to be set aside at compound interest for the life of the plant, at the end of which time the accrued interest should be sufficient to renew the plant, it is evident that
R(1 + R)n − R = C
or R = C
(1+r)n − 1