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Strainer-Type Filters and Disc Filters for Agricultural Microirrigation Equipment

ISO 9912-2:2013 standard specifies general construction requirements and test methods for microirrigation filters - strainer filters and disc filters (hereinafter called filters) - intended for operation in agricultural irrigation systems.

Terms and definitions

Strainer filter
Device containing one or more filter elements, such as a screen or a mesh, used for separating clogging material from water flowing through the device by collecting it on the surface of the filter element or elements.
Disc filter
Filter in which the filter element is a disc filter element.
Strainer filter element/filter element
Component of a strainer filter consisting of a perforated plate, a screen, a mesh, or a combination of these, intended to retain clogging materials larger than a specified size from the water flowing through the component.
Disc filter element/filter element
Component of a filter composed of discs with grooved or textured faces arranged adjacent to the other to form a stack.
Filter housing
Component of a filter that houses or supports the filter element.
Filter housing cover
Removable cover permitting assembly, disassembly, inspection, and cleaning of the filter elements.
Drain valve/flush valve
Valve normally installed at the bottom of a filter, intended for draining or flushing of contaminate from the filter housing.
Nominal pressure/pnom
Numerical designation equal to the maximum working pressure specified by the manufacturer at which a device will operate at a water temperature of f 23 °C ± 3 °C.
Clean pressure drop
Pressure drop in a clean filter, measured with a flow of clean water.
Safe maximum pressure drop
Maximum allowable pressure difference, declared by the manufacturer, between inlet and outlet pressures across a filter, when the filter element has become clogged to the extent of requiring cleaning or replacement.
Critical pressure drop before failure
Maximum allowable pressure difference, declared by the manufacturer, between inlet and outlet pressures across each filtering element of the filter, which will not cause failure of the filter element.
Range of recommended flow rates
Range of flow rates, declared by the manufacturer, for proper operation of a filter.
Nominal size
Numerical designation used to refer to the size of the device end connection which is identical to the numerical designation of the pipe or pipes to which the device is to be connected directly.
Aperture size
Size, declared by the manufacturer, that expresses the ability of a filter to retain particles and suspended matter
Note: The aperture size is expressed in microns.
Filter connection length
Overall length between the extremities of the connections of a filter, the face-to-face distance between the connections, or the distance between centre-lines of the parallel inlet and outlet ports.
Debris, suspended particles of organic or inorganic origin, or other contaminants removed from water in the filtration process.


Each filter shall bear a readily visible, durable marking giving the particulars specified in the following

  1. Marking of filter housing
    The marking of the filter housing shall include:
    • The name of manufacturer and/or registered trademark,
    • The model identification,
    • The nominal size,
    • The nominal pressure,
    • An arrow indicating the direction of water flow,
    • The aperture size (optional marking, applicable when a filter is supplied with the filter element already assembled).
    The aperture size may be marked on an adhesive label affixed to the filter housing in a prominent position.
  2. Marking of filter element
    The marking of the filter element shall include:
    • The name of manufacturer and/or registered trademark, and
    • The aperture size.
    The aperture size may be indicated by a marking such as a specific colour that is defined in the Manufacturer's catalogue.

Design and construction requirements


Filter parts that are in contact with water shall be made of non-toxic materials and shall be resistant to, or protected against, corrosion and other forms of degradation caused by existing working conditions and types of water and chemicals used in agricultural irrigation. The filter housing shall be resistant to environmental conditions.

Components belonging to filters of the same size, type, and model, and produced by the same manufacturer, shall be interchangeable.

Plastics parts of a filter that are exposed to ultraviolet (UV) radiation under normal working conditions in which the filter operates shall include additives to improve their resistance to UV radiation. Plastics parts that enclose waterways shall be opaque or shall be provided with an opaque cover that blocks all light from reaching clear waterway enclosures.

The construction of the filter shall facilitate its proper installation in its intended location and position.

The filter shall be designed so that, after the assembly of the filter element in the filter housing, all the water flowing through the filter flows through the filter element.

Filter housing

Where the size or the configuration of a thread-connected filter housing does not allow for easy handling of it while connecting or disconnecting pipework, a boss or other means for facilitating connection and disconnection of the filter housing to and from the network shall be provided.

The filter shall be designed so that contaminates accumulated on the filter element or in the filter housing do not enter the supply line when cleaning or replacing the filter element. In a manually cleaned filter, the construction of the filter element shall allow the disassembly, cleaning, and reassembly of the filter element without removal of the filter from the supply line.

The filter connection length shall not deviate from the length indicated in the manufacturer’s catalogue by more than the tolerance specified in Table 1.

Table 1 — Filter length tolerance
Dimensions in millimetres
Length of filter Permissible deviationa
≤400 ±2
>400 ±3
a The length tolerance is only applicable to filter housings where the axes of inlet and outlet ports are parallel.


  1. Threads of a filter with threaded ends for direct connection to the supply line shall comply with ISO 7-1. Other types of threads are allowed provided that a suitable adaptor is supplied with each threaded connection, so that it complies with ISO 7-1.
  2. Flanged connections shall comply with ISO 7005-1 or ISO 7005-2, depending on the material from which the filter housing connection is made.
  3. For filters with other types of connections, the filter manufacturer shall supply or identify a commercially available adaptor to a standard thread as described in1 or to a standard flange as described in 2.
  4. A suitable connection, such as a thread or a mechanical grooved connection (Victaulic1), for example), shall be provided on the drain valve outlet to facilitate the connection of components to provide for drainage.

Mechanical and hydraulic tests

  1. General
    Perform the following tests with water at a temperature of 23 °C ± 3 °C, unless otherwise indicated in the specific test description.
    Ensure that the instruments used for measuring the various parameters permit measurement to an accuracy of ± 2% of actual values.
  2. Resistance of the filter to internal hydrostatic pressure.
  3. Filter element tightness and resistance to buckling or tearing.
  4. Clean pressure drop.

Information to be supplied by the manufacturer

The following information shall be supplied by the manufacturer:

  • The name of manufacturer and address of manufacturer or supplier;
  • The model and catalogue number of filter;
  • The filter data:
    • Nominal size (a single number designation is adequate if the inlet and outlet ports are the same size);
    • Nominal pressure;
    • Critical pressure drop before failure, for each type of filter element;
    • Range of recommended flow rates;
    • Overall dimensions of filter;
    • Type of connections to piping network;
    • Filter connection length;
    • Aperture size;
    • Curve of clean pressure drop in the range of recommended flow rates;
    • Safe maximum pressure drop;
  • The housing cover closing instructions;
  • The instructions for assembly, operation, cleaning, and maintenance, including the limitations and prohibitions;
  • The list of spare parts;
  • The resistance to chemicals commonly used in agricultural irrigation.

For more information please see ISO 9912-2:2013 Agricultural irrigation equipment -- Filters for microirrigation -- Part 2: Strainer-type filters and disc filters.

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