RELIABILITY TESTS OF PULSE WIDTH MODULATION (PWM) VALVES FOR FLOW RATE CONTROL OF ANHYDROUS AMMONIA

Pulse-width-modulation (PWM) offers the potential to improve anhydrous ammonia application accuracy and control. The solenoid valve used in the manifold is central to the PWM metered anhydrous ammonia applicator. Valve durability plays a major role in acceptance by the farmers and provision of warranty by the manufacturer. This article describes a test program to determine the reliability of PWM valves through detection of failure by flow and pressure. The Success Run Theorem was applied to estimate the reliability of the valves at 3.2 million cycles to be 84%, with a 90% confidence level.