1-11 - Lecture 12 Center Pivot Design Operation I...

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Sprinkle & Trickle Irrigation Lectures Page 145 Merkley & Allen Lecture 12 Center Pivot Design & Operation I. Introduction and General Comments A ntries Typical lateral length is 1,320 ft (400 m), or ¼ mile The lateral is often about 10 ft above the ground Typically, 120 ft pipe span per tower (range: 90 to 250 ft), often horsepower electric motors (geared down) lower labor costs than periodic-move sprinkler systems Center pivot maintenance costs ca complex machine, operating under “field” conditions re pipe, the entrance velocity is a bit high at 3 m/s Typical lateral operating pressures are 140 - 500 kPa (20 to 70 psi) other Corner systems are expensive; can operate using buried cable; corner systems don’t necessarily irrigate the whole corner Without a corner system or end gun, π /4 = 79% irrigated fill root zone at g topography Center pivots are used on about half of the sprinkler-irrigated land in the US Center pivots are also found in many other cou with one- At 120 ft per tower, a 1,320-ft lateral has about 10 towers; with 1-HP motors, that comes to about 10 HP just for moving the pivot around in a circle The cost for a ¼-mile center pivot is typically about $55,000 (about $435/ac or $1,100/ha), plus about $20,000 (or more) for a corner system For a ½-mile lateral, the cost may be about $75,000 (w/o corner system) In the state of Nebraska there are said to be 43,000 installed center pivots, about 15% of which have corner systems Center pivots are easily (and commonly) automated, and can have much n be high because it is a large and fairly The typical maximum complete rotation is 20 hrs or so, but some (120-ac pivots) can go around in only about 6 hrs IPS 6” lateral pipe is common (about 6-5/8 inches OD); lateral pipe is generally 6 to 8 inches, but can be up to 10 inches for 2,640-ft laterals Long pivot laterals will usually have two different pipe sizes Typical lateral inflow rates are 45 - 65 lps (700 to 1,000 gpm) At 55 lps with a 6-inch The end tower sets the rotation speed; micro switches & cables keep towers aligned of the square area is For a 1,320-ft lateral (without an end gun), the irrigated area is 125.66 acres or design purposes, usually ignore soil WHC (W F a Z); but, re each irrigation (even if daily) Center pivots can operate on very undulatin Some center pivots can be moved from field to field Below are some sample center pivot arrangements
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Merkley & Allen Page 146 Sprinkle & Trickle Irrigation Lectures
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Sprinkle & Trickle Irrigation Lectures Page 147 Merkley & Allen
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Some pivots have an end gun that turns on in the corners, in which all other sprinklers shut off via individual solenoid-actuated valves. The pivot stops in the end gun runs for a few minutes. down in the corners, turning on an end gun, but leaving the running (at lower discharges) like extra capacity in the center pivot so they can shut off y times of the day, and still complete the irrigations in time tectors so that sprinklers in the corner arm n groups) as the arm swings out and then ain
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