Irrigation systems world wide are dependent on sound pressure management techniques which are normally incorporated at the design phase of the project. This holds true whether you are designing agricultural irrigation systems incorporating drip, micro spray, sprinkler or pivot systems and has similar ramifications for turf irrigation or even golf course irrigation systems. Automatic Control Valves are used to manage pressure and provide pressure relief, this article discusses those most commonly used in agricultural systems.
In the case of drip or micro irrigation it is vitally important to not over pressure these devices as they are built to respond to very low pressures and overpressure can result in damage to the emitters or spray units or the low pressure piping system. Having reliable low pressure is extremely important. Often on very large drip or spray systems, you will have higher pressures near your water source (often a pump) and will have lower pressures at the extremities of the system due to pressure loss in the piping system. Controlling the higher pressure close to the source is an important consideration when designing the system.
When considering sprinkler irrigation maintaining the pressures within the recommended operating range of the manufacturer is also critical. If you exceed the recommended pressures then your sprinklers will end up misting and if in a windy environment, your water is being wasted. If your pressures are too low then your sprinklers will end up having a doughnutting effect where you will not have good water distribution near the actual sprinkler.
Pressure matters! The larger the system, the greater the need to carefully analyze your pressure requirements. A qualified irrigation consultant will make sure that a hydraulic study is completed on the proposed system and that pressures throughout the system are within the pressure range of the piping network and the irrigation manufacturer’s equipment.
Pressure Relief is also vital in irrigation design. If you are incorporating pumps in your system, you may have surges or transients when starting up or shutting down. You may also have numerous irrigation solenoid valves turning off and on which can add to system surges. It is good practice for the irrigation consultant to review any potential surges within the system and by utilizing pressure relief valves, enable you to dump excess pressure to atmosphere when pressures go above the maximum levels.
Automatic Control Valves are used to manage pressure and provide pressure relief, here are the most common we see used in agricultural irrigation systems:
Standard Pressure Reducing Valve
This type of valve is available from 50 mm to 900 mm and manages downstream pressures and is usually offered in ductile iron with a heat fusion epoxy coating. For most irrigation applications you will find ANSI drilling on the flanges being either PN 10 or 16. Models 75 mm and smaller are available in Thread (BSP) or Flange while larger sizes are only available in flanged offerings. The advantage that automatic control valves offer is that they always maintain a constant downstream pressure regardless of fluctuation upstream pressures unlike direct acting pressure reducing valves where the pressure will change as flows change. These valves are also known as a hydraulic control valves as the valve requires no electricity and the pilot is fully adjustable so that you can change the downstream pressure by simply adjusting the nut on the pilot to change the downstream pressures. These types of valves require a differential pressure (pressure drop) across the valve of about 6 meters to operate effectively, so the designer must ensure it is designed for a reasonable pressure drop across the valve.