12 BULLETIN 479, U. S. DEPARTMENT OF AGRICULTURE. 



From each faucet of a system so installed an area of 3,000 square 

 feet can be watered by means of a nozzle. If lawn sprinklers are 

 used the spacing of the faucets on each pipe line should be regu- 

 lated by the distance to which the spray can be thrown when several 

 sprinklers are in use. Twice this distance will determine the spacing. 

 Thus if the spray can be thrown in a radius of 10 feet the faucets 

 should be 20 feet apart. 



The pipe should be sunk deep enough to allow the use of plow 

 and harrow in preparing the ground; and where there is need for 

 water all winter, the system should be buried deep enough to avoid 

 the danger of freezing. 



The longer the pipes the smaller their diameter, and the less the 

 head of water the greater is the decrease in flow through friction. 

 It follows that to obtain the same flow per unit of time the head of 

 water must be greater when small than when large pipes are used, 

 and that with a given head and quantity the greater volume of 

 water will be available for use if it is conducted to and through a 

 nursery in large pipes. It is often difficult to control the length of 

 the pipes and the head of water. The size of the pipe used, however, 

 is entirely within control. In order to secure sufficient pressure to 

 run 10 or 12 sprinklers at the same time there should be a head of 

 water not less than 50 feet; the main pipe should be 3 or 4 inches 

 in diameter (the latter is preferable) ; and the laterals and stand- 

 pipes should be 1| or 2 inches in diameter. One system which 

 embodies these features has over 4,000 feet of main-line pipe, but at 

 its lower end it carries 75 gallons of water per minute. 



To facilitate its cleaning out, a water reservoir should have an 

 outlet besides that of the distributing pipe line. To prevent sand 

 or gravel from getting into the system and clogging nozzles or 

 sprinklers, the pipe at the intake should be covered with both a 

 coarse and a fine screen. 



There should be one gate valve next to the reservoir, one on the 

 main pipe just before it reaches the nursery area, and one at the 

 junction of each lateral with the main pipe. The pipe line should 

 have union connections at intervals of approximately 100 feet and 

 at the junction of branches. These will make it unnecessary to dig 

 up the entire line when there is a part to be mended. There should 

 be a plug or preferably a gate valve at the lower end of the main 

 and of each branch of the pipe line. These will permit the washing 

 out of the pipes in case they become clogged or obstructed, and 

 also their draining for the winter. All of the unions and any of 

 the other important parts of the underground pipes should be clearly 

 marked on the ground itself in some manner, such as by boxed 

 openings or slightly projecting stakes. Finally a very careful dia- 

 gram of the system, on which all of its parts are clearly indicated, 



