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Sprinkler performance criteria



These relate to the ability of the sprinklers to provide a uni­form pattern of "rainfall" on the ground surface.

Droplet size distribution.A range of droplet sizes is produced as the water stream breaks up leaving the nozzle. Larger droplets will have a greater momentum and therefore travel further from the nozzle, but will increase the risk of soil and even plant damage (for ex­ample, to flowering parts). Small droplets may be preferred, but will be much more susceptible to wind drift and evapora­tion in the air, thereby reducing application efficiency.

Smaller droplets are achieved with higher pressures and/ or smaller nozzle sizes.

Wetted diameter and sprinkler spacing.The diameter of the wetted area increases as nozzle size and pressure increase. The relationship is not linear, that is, a dou­bling of pressure does not result in a doubling of wetted di­ameter, since the effects of droplet size come in to play.

The wetting pattern from a single sprinkler usually results in a large variation in depth of application, from maximum at die sprinkler position to zero at the perimeter of me wetted area. The pattern is distorted further by the action of wind. Consequently adjacent sprinklers must be positioned so their wetting patterns overlap. For rectangular spacing of sprinklers, me distance between sprinklers should be 0.55-0.75 per cent of the wetted diameter. The same applies to adjacent runs of self-propelled machines. Measurements of die actual wetting pattern in the field gives more accurate recommendations.

Sprinkler discharge. The flow rate from the nozzle also increases as nozzle size and water pressure increase, with a marked variation possi­ble. The sprinkler discharge for a given spacing determines the application rate to die field as follows:

where spacing is die distance between sprinklers along die sprayline, and shift is the distance between sprayline posi­tions. In the case of self-propelled machines, die travel speed influences die application rate: it is easiest to refer to die manu­facturer's specifications.




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