16 BULLETIN 155, U. S. DEPARTMENT OF AGRICULTURE. 
The experience with 6-inch blow-offs on the Kings Hill pipes was 
similar. Silt in the nipples became so compact that water could not 
be forced through, and small holes were bored through the pipe to 
drain it. Then the valves were removed and cleaned. Flushing 
the valves occasionally would perhaps obviate this trouble. Where 
the water carries extraordinary quantities of sand or silt it may be 
advisable to provide sand boxes near the intakes. This was done 
on the Santa Ana Canal in California,’ the lower Yakima Irrigation 
Co.’s canal in Washington, and on other canals. 
On the 31-inch siphon at Prosser, Wash., a 12-inch valve was 
used. (Sunnyside Canal, U. S. Reclamation Service.) 
Where pipes are 
kept full during the 
winter, alr valves and 
blow-off gates should 
be protected against 
freezing. : 
CONNECTIONS WITH OTHER 
KINDS OF PIPE. 
On the Sunnyside 
Canal in Washington 
the portions of the 
Mabton and _ Prosser 
siphons at intake and 
outlet ends where the 
pressures are light are 
made of concrete pipe. 
These are joined to 
continuous stave wood 
Fic, 5.—Forty-eight-inch special tee for joining wood pipes which sustain 
pipe to cast-iron pipe. 



the greater pressures. 
In other pipe lines wood is used for heads up to approximately 200 
feet, and steel or cast iron for greater pressures. Again, where 
curves too sharp for the wood pipe are required, in passing under 
railroads and in other situations, it is frequently found necessary to 
join continuous stave pipe to that of some other type. , 
A common practice in joining wood and cast iron or steel is illus- 
trated by Plate III, figure 2. The wood pipe is made to overlap the 
metal pipe, and by means of the bands is cinched up to make a tight 
joint. The usual lap is 12 to 18 inches, but laps of as much as 4 
feet have been made. 
A connection of this kind is criticized on the ground that it does 
not permit proper saturation of the wood pipe where it overlaps the 
1 Trans, Amer, Soc, Civ. Engin., 33 (1895), p. 129. 

