COST OF POWER.
515
TABLE XXXIX.—Expenditure of Power in Watt-hours per Cycle.
Load.
4 Ton. i Ton. 1 Ton. 11 Ton. 1| Ton.
Hydraulic crane, Electric ,, 82'0 48-5 127'2 58-5 127'2 73'5 172'4 80'5 172'4 105'5
A test with two crânes at Glasgow, carried out by Mr. Baxter of the
Clyde Navigation, was analysed by Mr. Walter Pitt* in the same units.
The lift in this case was 30 feet, the slew 100°, and the lower 10 feet. The
hydraulic crane had only one power, and consequently was at a great
disadvantage in regard to the lighter loads. At its full load it exhibited
a superiority to the electric crane.
TABLE XL.—Expenditure of Power in Watt-hours per Cycle.
Load.
1 Ton. 2 Tons. 2| Tons. 3 Tons.
Hydraulic crane,. . . 236'7 Electric ,, • • • 83'3 236'7 160'4 236'7 197'9 236'7 241'9
Cost of Power.—Greater expenditure of energy does not necessarily
involve a correspondingly greater cost of working. This, of course,
dépends on the relative rates at which power can be supplied, and will
vary with different localities. Equal conditions prevail when the cost of
water under pressure bears to the cost of electricity the ratios given in
Table xxxvii. Thus, electricity at 3d. per Board of Trade unit is the
equivalent of water under 750 Ibs. pressure at 3 x 6'52 = ls. 7|d. per
1,000 gallons.
A comparison of the cost of hydraulic power and electric supply as
compiled by Mr. Ellington t from the Reports of the London Hydraulic
Power Supply Company (L.H.P.), and the Westminster Electric Supply
Corporation (W.E.S.), for the year 1894, yielded the following results :—
* Pitt on “The Modern Equipment of Docks,” Eng. Conf., London, 1903.
tEllington, “Notes on Hydraulic Supply in Towns,” Proc. I. Mech. E.,
July, 1895.