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BULLETIN 906, U. S. DEPARTMENT OF AGRICULTURE. 



done by building a screen completely around the outlet pipe. Some 

 screens are built in the form of a long narrow trough which is 

 screened on all sides, the outlet being beneath the screen. Such a 

 screen can be set in an open ditch that is widened out a little at the 

 pipe inlet. 



Screens have also been designed that are self cleaning, reliance 

 being placed on the velocity of the water to keep the screens open. 



Care should always be taken to prevent trash entering a ditch or 

 pipe line where water is finally distributed through orchard hydrants 

 having small openings. It is especially necessary to take proper 



Fig. 6. — Settling basin and screens. 



precautions at the intake where the water is diverted from a flowing 

 stream. For comparatively small heads of water it is sometimes 

 possible to bury the first 20 or 30 feet of pipe under the stream bed 

 laying the pipe with open joints and covering it with gravel. This 

 will prevent all floating material entering the pipe and should keep 

 out the sand. Some comparatively large mains have been protected 

 at the intake in this manner. 



Open ditches bordered by shade trees are continually gathering 

 leaves which are particularly harmful in clogging screens, as the 

 leaves will flatten out against a fine mesh screen and may completely 

 obstruct the flow of water. 



Where pipes are fed by open ditches and have sufficient grade so 

 that the velocity of water will transport sand or small gravel, the 



