مطالعه آزمایشگاهی عملکرد شیر کنترل دبی: اثر سختی فنر و مونتاژ قطعات

در سامانه های آبیاری تحت فشار، توزیع یکنواخت آب اهمیت بالایی دارد. یکی از ابزارهایی که به این منظور به کار می‌رود شیر کنترل دبی است. شیر کنترل دبی مورد مطالعه در این تحقیق قطعه ای است دوکی شکل و به واسطۀ وجود یک فنر، به نحوی در روزنه ای با قطر مشخص حرکت می کند که با تغییر فشار، همواره دبی تقریباً ثابتی از خود عبور دهد. مبانی طراحی شیر کنترل دبی مورد مطالعه سال 2015 ارائه شد اما تاکنون به تولید صنعتی نرسیده است. این نوع شیر می تواند در سامانه های آبیاری نواری کم‌فشار به کار رود. خستگی فنر و نحوۀ نصب قطعات ممکن است عملکرد شیر کنترل دبی را تحت تاثیر قرار دهد. در این تحقیق به بررسی آزمایشگاهی این عوامل بر عملکرد این شیر پرداخته شده است و محدودۀ مجاز تغییرات آنها به شکلی که تاثیر قابل توجهی روی عملکرد شیر کنترل دبی نداشته باشد به دست آمد. نتایج بررسی ها نشان داد که اگر فاصله نصب دوک از روزنه، b، و سختی فنر، k، به ترتیب تا 82 و 15 درصد بیشتر از مقادیر طراحی تغییر کند، عملکرد شیر کنترل دبی کمتر از 5 درصد تحت تاثیر قرار خواهد گرفت. تغییرات سختی فنر که ناشی از خستگی آن در دورۀ کارکرد شیر کنترل دبی است، می تواند بر عملکرد شیر کنترل دبی تاثیر گذارد. نتایج تحقیق همچنین نشان داد که برای شیرهای کنترل دبی 0/4و 0/6 لیتر بر ثانیه، به ترتیب تنها 6 و 3 درصد می توان خستگی فنر را نسبت به مقدار طراحی کمتر در نظر گرفت.

Experimental Study of Parameters Affecting the Performance of Discharge Control Valve: Effects of the Spring Fatigue and Valve Assembly

IntroductionWater distribution uniformity is a key in pressurized irrigation systems. Pressure fluctuations due to topographical changes, local and frictional head losses, and different water uses are anticipated. Any mechanical device with the ability to keep an almost constant flow delivery being irrespective of the pressure fluctuations is of great practical importance. In this regard, a flow control valve is a useful tool. A flow control valve is a mechanical choked orifice plate structure including a floatspring mechanism inserted in an ordinary orifice (Zhang and Wang 2015). Such a valve is not yet produced commercially.In this study, the effect of the spring elasticity mainly due to spring fatigue is investigated experimentally on the valve performance. Also, the changes in the installing location of the float, when the valve is in rest condition, may affect its performance. To quantify this effect a detailed experimental plan was performed. MethodologyThis study presents an experimental approach for testing the effects of the spring fatigue and spring installation location on the performance of the discharge control valve. In this regard, an experimental model was constructed at Imam Khomeini Intentional University, IKIU. It consists of a centrifugal pump, a motor drive to adjust the pump’s rotational speed, and a Rosemont digital pressure gauge. The flow rate was measured by a calibrated Venturi meter. Two design discharges of 0.4 and 0.6 l/s were considered and the valves were fabricated based on the design guidelines available at Rezazadeh et al. (2019).In order to quantify the valve performance PI index was used (Atashparvar et al., 2019).  (1)                                                      in which, DPID and DNID are the total/sumation of the positive and negetive discharge deviations from the design value respectively.Results and DiscussionAccording to the experimental curves of valves’ discharge variations, PI values were calculated to identify the effects of the spring fatigue and inappropriate valve assembly (Fig. 1 and Fig. 2). The results indicated that, if the distance of the float to the orifice location, b, varies in the ranges of 0.5£b(mm) £4.3 and 2.75£b(mm) £5 for Q=0.4 and 0.6 l/s respectively, the valve performance is affected marginally (Fig. 1). It is found that for the design discharge values of 0.4 and 0.6 l/s the spring elasticity can decrease no more than 3% and 6% respectively (Fig. 2).  Fig. 1 PIvalues of changing the distances of the float of MCOP  Fig. 2 PIvalues of changing the MCOP’s spring elasticities ConclusionsWater distribution uniformity is a key in pressurized irrigation systems. In this regard, flow control valve is a useful tool. The control valve studied in this investigation, consists of a float moving into an orifice of a given diameter. The mechanism makes it possible to have a semi constant flow rate being irrespective to the pressure fluctuations. The design criteria of the valve were proposed in 2015. It is notyet produced in commercial scale. Discharge control valve can be used in tape irrigation systems. Spring fatigue and inappropriate assembly can affect the valve performance. In this study, the effect of these parameters on the performance of the control valve are investigated experimentally. The results indicated that, if the distance of the float to the orifice location, b, and the spring elasticity, K, are considered 82% and 15% greater than their design values, the valve performance is affected less than 5%. Spring elasticity variations due to the spring fatigue can affect the valve performance significantly. It is found that, for the design discharge values of 0.4 and 0.6 l/s the spring elasticity can decrease no more than 3% and 6% respectively.