Projeto, construção e avaliação de uma servovalvula dosadora para sistemas de aplicação de fertilizantes liquidos a taxas variaveis

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

This work had as aim to project, to build and to evaluate a flow control servo-valve for liquid fertilizer application in variable rates, as well as to conceive a system with capacity for formulation and dosage in which the valve can operate. It was conceived a system capable to work with three concentrate formulations simultaneously, using three independent hydraulic circuits. Each one of these circuits should be endowed with a centrifuge pump capable to supply pressure and flow to the hydraulic line to make possible the flow control valve operation controlled electrically. A workbench was built for the experimental rehearses accomplishment, whose purpose was of evaluating its acting. This workbench represents a conceived system simplified circuit. A flow control valve can be considerate the most important element of the developed fertilizer application system. The initial proposal contemplated the use of solenoid drived valves by means of a PWM (Pulse Wave Modulation) sign; however this alternative was not shown technically viable. This way, it was necessary the new valve development to assist to the operation system requirements. The developed flow control valve mechanical driving is made through a servomotor. The flow control is made by means of a conical obturator. The valve behavior was evaluated, presenting good repetibility, presence of hysteresis and an answer typically quadratic. The hysteresis effect can be avoided being made the valve adjustment only in opening or closing operations. The quadratic answer does not represent a problem. Due to inflection problem, in the initial rate of the valve closing curve, this was restricted for values above 25%. After the valve has been evaluated and approved, tests were accomplished seeking the obtaining of a flow behavior experimental mathematical model in terms of its opening percentile and work pressure. The used experimental method was the 2k multifactor planning. The model evaluation criterion included the R2 determination coefficient calculation, a variance analysis and a residues analysis. Firstly it was obtained a linear mathematical model that presented a good adjustment according to the determination coefficient. It also presented a good statistical significance in agreement with the variance analysis. However, the linear model residues were not shown good, presenting tendency. Then, it was followed the quadratic mathematical model obtention. That also presented a good adjustment and a good statistical significance, differing for the fact of the observed tendency in its residues having been minimized in relation to the linear model. The quadratic model initially had the characteristic of overestimating the flow values, which was eliminated by means of a model constant term fine adjustment. The developed servo-valve and the obtained experimental model assisted to the aim of this work. The prototype of this work operated in a satisfactory way with the fluid work used. The mathematical model described the flow control valve behavior appropriately

ASSUNTO(S)

solos - fertilidade variable rates precision agriculture agricultura - mecanização eletronica na agricultura adubos e fertilizantes liquidos servo-valve liquid fertilizing agricultura e tecnologia adubos e fertilizantes - aplicação

ACESSO AO ARTIGO

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