132 
GRAVEL AND PLACER MINING IN ALASKA. 
[BULL. 263. 
Where 22- to 30-inch pipes are used it is not advisable to employ less 
than 14 gage, even under low heads, as lighter pipe will not bear 
handling. The practice of burying pipe, or at least sodding it over, 
where the line is to be in place for more than a 
season, is recommended in Alaska even more 
than in other countries. 
Air valves, which can be simply made of 
leather, hinged to the inside of 3-inch openings 
in the pipe, should be not more than 300 feet 
apart. These allow the air to escape when the 
pipe is being filled and prevent the collapse 
of the pipe when suddenly emptied of water. 
Leakage in joints may frequently be stopped by 
slowly feeding sawdust or manure in at the 
upper end. In case of collapse of a pipe line, 
experience has shown that by turning on the 
water slowly, after closing the lower end, the 
collapsed sections may be restored to shape for 
temporary use. The experiment is risky. 
PL XXII, B, shows the set-up of a hydraulic 
pipe line on McKee Creek, Atlin. As may be 
seen, the line is well braced and rock ballasted, and on steep places 
the joints are held by lugs and wire guys. The line, which is one of 
three in use on this propert} r , is of 12-gage steel, is 1,200 feet in length, 
has a 30-inch mouthpiece at the penstock, and is successively reduced 
to 18, 16, and 12 inches, the last discharging through the giant. 
At full capacity the discharge was said to be 700 miner's inches at 
170-foot head. The discharge was through a No. 4 Vancouver giant, 
using 6-inch nozzle, the average twenty-four hour duty being 4 cubic 
yards of gravel. Along the pipe line side ditches were cut for a short 
distance to take care of leakage. PL XXIII, A, shows a pipe line 
led down a hillside on Pine Creek, Atlin. 
Fig. 24.— Device for reen- 
forcing joints of pipe. 
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Fig. 25. — Device for setting pipe by battering. 
An important fact regarding the flow of water in pipes is the loss 
of effective pressure at the nozzle due to friction, owing to the use of 
pipes of too small diameter. The friction of water in pipes increases 
