Successful Farming - - IRRIGATION INSIDER - By Dave Mowitz, Ex­ec­u­tive Edi­tor, Ma­chin­ery & Tech­nol­ogy

Fields laid bare from har­vest of­fer a great op­por­tu­nity to in­spect cen­ter piv­ots for re­pairs or to eval­u­ate their per­for­mance be­fore putting them to bed for the win­ter. Steve Melvin of the Univer­sity of Ne­braska says many sup­pli­ers fea­ture ex­cel­lent off-sea­son ser­vice spe­cials at this time.

A key per­for­mance check that is of­ten over­looked is siz­ing up a pivot’s op­er­at­ing pres­sure. Also, mea­sur­ing a sys­tem’s flow will help with di­ag­nos­tics.

In or­der to check pres­sure, you’ll need a work­ing pres­sure gauge and an un­der­stand­ing of op­er­at­ing pres­sure de­sign for your sys­tem, Melvin ex­plains. The best place to find de­signed op­er­at­ing pres­sure and flow is to ref­er­ence the sprin­kler chart, which came with the sprin­kler pack­age when it was pur­chased new with the pivot or as a re­place­ment pack­age. This in­for­ma­tion is of­ten placed in the cen­ter pivot’s panel.

The sprin­kler chart is dif­fer­ent for al­most ev­ery pivot be­cause ev­ery pack­age is cus­tom de­signed for that sys­tem’s flow rate and length. The sprin­kler chart con­tains a lot of in­for­ma­tion, in­clud­ing:

• De­signed op­er­at­ing pres­sure and flow rate

• De­tails about po­si­tions of all the sprin­klers

• Length of each span and over­all length of the pivot

If you can­not find the chart, re­quest one from the dealer who sold you the sprin­klers.

pin­point pres­sure

Mea­sure pres­sure both at the pivot point and near the end of the pivot, Melvin says. “Check the pres­sure at the end of the pivot when the last tower is in the high­est point in the field. For the reg­u­la­tors to work cor­rectly the pres­sure in the pivot main­line needs to be at least 5 psi over the rated pres­sure of the reg­u­la­tor,” he says.

As­sum­ing the pres­sure was cor­rect when the sprin­kler pack­age was new, if the pivot’s pres­sure is now too high the cause is likely plugged noz­zles or re­stric­tions in the pipe­line.

If the pres­sure is too low, that can in­di­cate too much wa­ter is ex­it­ing the pivot (likely due to leaks) or that there is a prob­lem with the pump out­put. A flow me­ter is a help­ful tool in this sit­u­a­tion be­cause it will tell you if you have more or less wa­ter flow­ing through the sys­tem than the de­sign calls for.

“Some­times pro­duc­ers as­sume the flow me­ter is bad if the flow is dif­fer­ent than what the sys­tem is de­signed to pro­vide,” Melvin says. “If this is a con­cern, the flow me­ter can be re­moved and tested by the man­u­fac­turer.”

Low pres­sure with high flow rates in­di­cates that more wa­ter is leav­ing the pivot sys­tem than was de­signed to, Melvin says. The ex­cess flow can be com­ing from leaks, bad pres­sure reg­u­la­tors, or worn or miss­ing sprin­klers. Of­ten, these prob­lems can be seen by look­ing at the wa­ter pat­tern com­ing out of the pivot with the sun re­flect­ing on it in the morn­ing or in the evening. In a prop­erly func­tion­ing sys­tem, the wa­ter dis­tri­bu­tion should ap­pear even with a grad­ual in­crease in wa­ter vol­ume from the cen­ter point to the outer end.

Worn-out pres­sure reg­u­la­tors and sprin­klers can be hard to see, how­ever, so con­sider re­plac­ing them ev­ery eight to 10 years.

When look­ing at the sprin­kler pat­tern, also note bro­ken or miss­ing sprin­klers and dam­aged rub­ber boots where the spans con­nect.

If a sprin­kler needs to be re­placed, take it to the dealer or look it up in the sprin­kler chart so you get the cor­rect reg­u­la­tor and sprin­kler with cor­rect noz­zle size for that por­tion of the pivot.

An­other good way to eval­u­ate the sprin­kler pack­age is to look for non­uni­form cir­cu­lar pat­terns in the crop. Of­ten they be­come vis­i­ble aerial im­ages or, if bad enough, from the com­bine cab at har­vest. Do not rely on the com­bine yield mon­i­tor to pick up sprin­kler prob­lems, how­ever, be­cause those ar­eas are usu­ally fairly nar­row and the width of the com­bine head will of­ten col­lect grain from both poorly and well-wa­tered ar­eas, Melvin warns.

A great time to check sprin­kler pat­terns is in the morn­ing or evening light.

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