THE FLOW OF WATER IN WOOD-STAVE PIFE. 85 
manipulate, it was easy to alter the flow in either one so that three observations 
at widely separated velocities were possible on each pipe. During any one obser- 
vation the load on the power plant was held constant, variations in load being 
cared for by other plants. 
The observations on the 10-foot pipe indicate the capacity after 17 years' 
service was but 6 per cent less than that called for by our formula. As this is 
well within the range of difference between actual performance and formula for 
many of the relatively new pipes which formed the basis for the formula then, it 
would still appear that there is little or no depreciation in the capacity of stave 
pipes with the lapse of time. This statement, of course, excludes depreciation 
due to mud and gravel deposits. (See No. 62 below.) 
No. 62. Expt. S-20. 144-inch Untreated Fir Stave Penstock, Montana Power 
Co., near Ennis, Mont. — This pipe adjoins pipe No. 61 above, and the description 
of tests is found above. The capacity of this pipe was something less than 10 
per cent below that called for by our formula. The three observations, at veloci- 
ties ranging from about 3.5 feet per second to 7.3 feet per second, did not yield 
results as consistent as did those on the 10-foot pipe. 
ADDITIONAL CONCLUSIONS. 
Following nine years' experience in the use of the Scobey formula 
for capacity offered in this bulletin, the writer feels that there is no 
occasion to change any of the factors in it. A great many pipes of all 
sizes and with a wide range of velocities have been constructed under 
the guidance here offered and no adverse criticism whatever has re- 
sulted. A study of Table 9, column 19, shows that the data indicate 
a pipe capacity slightly above the quantities as computed by this 
formula. However, there are enough observations that show the 
opposite trend to prevent a change in the formula. 
The writer wishes to acknowledge indebtedness to the various 
organizations that have sent results of tests from time to time. He 
will appreciate future cooperation along this line and will welcome any 
information that will perfect our knowledge of the actual field capaci- 
ties of wood-stave pipes. 
