Solenoid Valves: Increase Efficiency And Economy For Irrigation Systems In agriculture, the economics of water supply and demand is driving the development of water conservation controls in irrigation systems. Across the entire world these pressures have made the improvement of the lowly hydraulic valve a key cost saving concern. Here, we present the types of valves most often used when building irrigation systems, and briefly touch on their different features. The most important considerations when selecting valves are quality, field reliability, and the suitability of design. Yet replacing a bad valve with a better one may be a simple but invaluable upgrade that permanently resolves costly recurrent failures and inadequacies. 1
Gate Valve Also called sluice valves or shut off valves, gate valves are typically used at the main water feed, or at the entry points to subsections of a field independent to other areas. A gate valve operates by sliding a flat or wedge shaped gate into a seating array much like a gate slides down to cover a shop front, thus creating a clean, tight seal. Gate valves should only be used to cut off water flow; when used for any other purpose the quality and longevity of the valve quickly deteriorates. Because of this, gate valves should never be used to regulate or adjust water flow. Gate valves are compact valves that require little energy to open or close, and are capable of completely obstructing water flow in both directions (no directionality). When used properly, the seal surface and seating are difficult to degrade. Gate valves are suitable for use at all scales, from micro to macro. Manually operated gate valves usually use cranks attached to threaded stems (i.e.: screws). Solenoid valves (see below), in contrast, do not have threading on their stems. In both solenoid and gate valves, the valve stems may be exposed, where they can be seen rising as the valve is opened; these are called rising gate valves. In contrast, non rising valves have stems that are enclosed within a self contained apparatus, and the movement of the stem cannot be seen. The gates on gate valves are also divided into those with flat plates, or wedges. Wedges are stronger and more durable than the simpler plate style. 2
Globe Valve Also called stop valves, globe valves are most often found in irrigation systems applications where the pipe size is less than DN 50 mm (2 inch) range. Globe valves create a seal when a threaded valve stem is rotated. As the stem is rotated, it applies pressure that moves the valve stopper (or disc) towards the valve seating, to either partially limit flow or fully restrict it. Globe valves are the most widely used and most popular of all valves for the following reasons: When establishing a seal, friction is minimized. Because friction is minimized, the valves are durable. The distance required for a secure seal is small. They are easy and cheap to produce. They are easy to repair. They may be applied in either low pressure or high pressure environments. Globe valves, like gate valves, may be used to fully prevent cut off water flow, but unlike gate valves they may also be used to regulate flow without fully cutting it off. Globe valves are unidirectional, and must be installed relative to the intended flow of the liquid. Globe valve casings tend to be larger than gate valves, and their operation is slower than that of a gate valve. While globe valves provide a longer lasting regulating capability than gate valves, as time goes by their overall seal tend to erode more quickly in comparison to other valves. Globe valves come in three main types: straight flow valves, angled valves, and Y type valves. 3
Butterfly Valve Butterfly valves regulate fluid flow by rotating a flat disk around an axis that spans the valve opening. It gets its name because the disk is typically bisected across its axis by an axle, which makes it look like a butterfly's wings. A butterfly valve can fully cut off fluid flow with only a 90 degree rotation; thus (along with ball valves, below) they are sometimes called quarter rotation valves. A butterfly valve's disc must exactly match the diameter of the valve's seal. Butterfly valves are small and lightweight relative to other valves, and tend to use fewer materials. These valves are a simple design that opens or closes quickly. Butterfly valves, like globe valves, can be used to either regulate or fully cut off water flow. Overall resistance (drag) is generally low, so in any size butterfly valves need little work to operate. This economy of force makes butterfly valves extremely useful for pipes of very large diameters. Because of this economy of work, simplicity of design, overall durability, and rapid responsiveness, butterfly valves are the preferred choice where gate or globe valves are inappropriate. 4
Ball Valve Ball valves use a perforated ball that is rotated along an axle to cut off or regulate fluid flow. Because ball valves are adjusted within a 90 degree range of motion, they are (like butterfly valves, above) also considered a quarter rotation valve. The work of operating ball valves is light and convenient compared to globe and gate valves. In comparison to other valves, the mass of a ball valve is small relative to the pipe's diameter, making them preferable for large caliber mechanisms. The seal of a ball valve is strong and reliable because the ball mechanism is simple and uncomplicated. Ball valves are thus easy to maintain, and have an extremely long lifespan. Unlike globe valves, ball valves may be habitually kept in the closed state without fear of eroding the seal quality. Ball valves are generally divided into either floating ball valves, or trunnion ball valves. In floating ball valves the ball is not fixed, so the seal is created when water pressure against the ball pushes it back against the rear seating. Trunnion valves set the ball into place using an affixed trunnion, so the seal in this case is as water pressure pushes the front seating backwards, against the ball. Floating ball valves are used for lighter pressured applications, and trunnion ball valves are used for applications with higher pressures. 5
Check Valves Check valves may also be called a clack valve, non return valve, or one way valve. The purpose of this valve is to stop the back flow of a fluid to make sure the flow does not reverse direction. Check valves are reactive, with the movement of the fluid itself automatically closing or opening the seal. Check valves for irrigation systems come in two main types: 1) In a lift check valve, the disc that forms the seal (also called a lift) opens when fluid pressure lifts the piston from its seal. The stopper in a lift check valve is connected at its center to a stem that is guided along a vertical track. When fluid pressure is no longer great enough to lift the stopper off the seating, the valve closes, and stays in place until water pressure once again rises to an appropriate level. Lift check valves may be designed to control the flow of water along either vertical or horizontal pipes. 2) The swing check or tilting disc check valve is also common in irrigation systems. Swing check valves typically mount the disc to a trunnion that is attached to the outside seating by a hinge. The disc then swings in and out of place along this hinge. If flow is reversed, the stopper snaps into place. When the flow resumes its proper direction, the stopper opens. Swing check valves may also use a trunnion design, where the disc is divided into double or multiple sections that are attached to a stationary trunnion that spans the seal's mouth. 6
Pressure Reducing Valve, or PRV A pressure reducing valve automatically reduces pressure within a pipe once a preset pressure target is hit. After a PRV is triggered, the pressure within the pipe must fall to another preset pressure (called the blow down factor), which is usually around 50% of the pressure that activated the PRV. There are many types of pressure reducing valves, but the two main ones currently used in agriculture irrigation systems are the piston and the spring loaded membrane types. Piston types rely upon pressure exerted upon a piston where the piston is pushed out of place once the pressure increases beyond the weight of the piston, and then the piston slowly moves back into place as pressure decreases. Spring loaded membrane types, however, rely on a more complicated assembly, where a spring activated diaphragm snaps in and out of place according to presets that are manually adjusted by manipulating the spring. Solenoid Valves for Irrigation Systems As agricultural technology advances, farmland irrigation is increasingly applying electronic automation and control networks. These networks require a large variety of solenoid valves that include pistons, diaphragms, as well as electric and latched control designs. These days, most solenoids are of the pulse variety, where a pulsed electrical current must be maintained via either a battery or some other electrical 7
source. At these scales, solenoids are the more efficient and economical alternative. When a check valve or pressure reducing valve (PRV) is required, solenoids are probably not the best fit; but in every other case gate valves, globe valves, ball valves, or butterfly valves a solenoid solution is likely already available, and should be carefully considered. For automated agricultural irrigation systems, the choice of valves is one of the primary factors in overall efficiency. IrriRich automated solenoid valves deliver stable reliability over the long term, demand no special environmental requirements, and are broadly applicable to agricultural conditions. IrriRich solenoids feature incredibly low head loss. Our solenoids deliver significant savings over the long term for any farmland irrigation systems, and come in a wide range of dimensions, starting at 1/8 inch to ½, ¾, 1, 1½, 2, 3, and 4 inches. Made from reinforced nylon and UPVC, IrriRich solenoids valves can be applied for manual or automatic controls. IrriRich provides manual control valves, two way electric control valves, three way electric control valves, pressure reducing valves, electrical activated pressure reducing valves, and supply quick pressure relief valves, pressure sustaining valves as well. Finally, all IrriRich valves feature our special anti rodent biting technology, giving our valves an increased irrigation systems field ruggedness that no other valve can claim. 8