AMIAD - AUSTRALIA & ASIA PACIFIC NEWS - VOLUME 9 - APRIL 2017 MARCH 2014 Vol.3 | Page 9

Table 2: De-rating factor for good, average and poor water qualities The inherent nature of a screen with its high open area will tend to run at a very low head loss until the majority of the screen is blocked and then will quickly rise to the trigger point of 5 Metres. This means the majority of the time the filter will run at low head loss’s of around 1 m. Step 7: Maximum Operating Pressure An important consideration when determining maximum flow is the open area of the screen, not the total area of the screen De-rating factors for filters will vary but can be well over half of their recommended maximum flow rate where high TSS conditions exist. It is also important to know if the water conditions change seasonally and to design where possible for the worst conditions. Table 2 shows the relationship and de-rating factor for different water qualities. Maximum operating pressure of a Filter relates not only to the structural strength of th e housing and components but, importantly, the forces exerted on the screen element itself. Suction auto filters generally do not require more than a 40 m differential to clean so consideration of throttling the discharge or exhaust valve is important to increase the longevity of the screen. Step 6: Selecting Inlet & Outlet diameters Selecting a clean head loss of less than 1 metre is recommended for sizing the inlet/outlet pipe size of the filter. The designer should also consider that prior to cleaning the Filter head loss will increase to the set point of the pressure differential (PD) switch which is general would be 5 m. Throttling the exhaust valve can increase the longevity of your system The bottom line Suction auto filters are reliable and an economical options for protecting your system. They generally will use less water than other technologies for cleaning and have the smallest footprint. If these basic design criteria’s are adhered to you can expect long term, reliable operation. THE AUTHOR: Clean Head Loss Chart PAGE 9 - March 2014 David Thompson || Amiad Australia Business Development Manager Irrigation Division E: [email protected] This article was published in Irrigation Australia, Vol. 29 No04