PRESSURE REGULATION
Knowing the basics of hydraulic control is a step toward successful irrigation.
BY MICHAEL MEYER A
gricultural irrigation systems generally require adequate and constant pressure in order to operate efficiently while minimizing problems. In areas that have unavoidable pressure drops and spikes, the system may require certain control valves, regulators or compensators to protect and enable the system to perform as efficiently and uniformly as possible.
These controls have functions such as pressure regulation, pressure sustainment, pressure relief and pressure compensation. Knowing which function is necessary and where to use it takes knowledge and experience and can make or break a system design. At the same time, these products must be sized and rated for the given flow rates and pressures in order to function properly.
In order to fully grasp the design concepts of when and how to use these products, it’s important to understand their different functions and terminology. As mentioned, the main hydraulic controls to improve uniformity and distribution include pressure regulation, pressure sustainment, pressure relief and pressure compensation.
REGULATING & SUSTAINING VALVES Pressure regulation typically refers to any device that reduces higher and sometimes varying upstream pressures to lower constant downstream pressures. Regardless of the incoming pressure and flow rate within a certain range, the regulator must be able to maintain the set pressure downstream. More often than not, it also must be able to respond quickly to changing upstream conditions with minimal variations in performance.
The two most common regulators are pressure regulating control valves and inline hose regulators. They are most often installed at the head of a hose, head of a manifold or head of a submain. Hose regulators are typically nonadjustable whereas most regulating valves are adjustable. They are both used in order to protect downstream systems from over-pressurization. Sizing pressure regulators is very important because they all work within a given flow range. The valves need a certain velocity and pressure loss across them in order to function properly. If the system flow rate is too high or too low, the valve will most likely fail and inevitably cause problems or breaks down the line.
Opposite to pressure regulating valves, pressure sustaining valves control and maintain a desired upstream pressure, regardless of fluctuating flow or downstream pressure variations. The valve will gradually open or close in order to maintain the minimum preset upstream pressure. If the pressure upstream of the valve is less than the setpoint on the valve, it will remain closed. As the pressure increases it will start to open the valve, and once the line pressure exceeds the setpoint on the valve, the valve will fully open.
This pressure reducing and sustaining valve has a three-way manual selector and can sustain upstream pressure and reduce downstream pressure.
Winter 2021 | Irrigation TODAY 9
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