62 
On Water Supplies suited to 
When water- and wind-power fail, recourse must be had to 
heat engines, of which three kinds are available — steam-, gas-, 
and hot-air engines. Where these have to be employed, it is 
best so to arrange the size of the engine and the capacity of the 
storage-tanks that a sufficient supply of water may be pumped 
up in about five hours' work every second or third day. The 
reason for this is, that heat engines require more or less super- 
vision all the time they are at work, and hence the cost of the 
attendant, which would be no greater for a large than for a 
small engine, would outweigh all other expenses, unless the 
hours of work are limited as much as possible. In the case of 
a homestead requiring a supply of 2000 gallons per day, the 
rate of pumping, if the machinery be worked five hours every 
third day, would be ^^^^ gallons X 3 da)s __ g^iiQ^s per 
0 hours X faO minutes 
minute ; and if the lift, together with the friction of the pipes, 
be 166 feet, then the horse-power required will be 
20 gallons X 10 lbs. X 166 feet , , 
= 33,000 = ^ horse-power. 
The pumps, with their motor, may be placed in any con- 
venient situation if the water to be pumped is near at hand, 
and not more than 20 feet below the level of the pumps ; but if 
the source of supply be at a distance, considerable care must be 
taken in the arrangements. Long suction-pipes are objection- 
able, because of the difficulty of laying them quite free from 
leaks, and leaks are very prejudicial to their efficiency. In 
addition, the force available to cause the water to flow in a long 
suction-pipe is limited to the atmospheric pressure, which 
corresponds to a column of water 34 feet high, that is to say, a 
pump capable of creating a perfect vacuum would suck water 
tip to that height ; but a perfect vacuum is never attained in a 
pump, hence it is not well to count upon more than 22 feet 
head, and therefore the actual lift of the water and the head 
of friction in the pipe, taken together, must not exceed that 
amount. ^ 
Suppose the water to be at a distance of 1000 feet, the suction- 
pipe to be 2 inches in diameter, and the quantity of water to be 
drawn through to be 20 gallons per minute, then from our 
diagram (Fig. 3) we find that 20 gallons per minute through a 
2-inch pipe will require a hydraulic gradient of 1 in 71, hence 
the friction of the pipe will be i^^^ — = 14 feet, and con- 
sequently the actual lift of the water must not be more than 
22 feet — 14 feet = 8 feet. As the motion of the water in the 
pumps is generally intermittent, the suction-pipe close to the 
pump should be fitted with an air-vessel about ten times the 
