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Agricultural Irrigation Equipment - Filters - Verification of Filtration Grade

ISO 18471:2015 Standard specifies a test method for the verification of filtration grade of filters intended for operation in agricultural irrigation systems. It is intended to be used for verifying the filter manufacturer's declaration about the filtration grade of a specific filter. This test method may also be used by a filter manufacturer to determine the filtration grade.

This test method uses a Clogging Capacity Meter (CCM) device to compare the filtration grade of the filter under test against the filtration grade of a test filtration screen.

Terms and definitions

For the purpose of this document, the following terms and definitions apply.

Filtration grade
Number, declared by the manufacturer, that represents the size of water passages in a filter and is related to its ability to stop particles.
The filtration grade is expressed in micrometres (μm. microns).
Clogging capacity meter (CCM)
Device used for measuring the time to reach a specified pressure loss across a standard filter screen, at a constant flow rate.
Aperture width
Distance between two adjacent parallel wires in a square-mesh wire cloth screen plain-weave.
Mesh count
Number of apertures per unit of linear measure in a woven wire cloth or wire screen.
Flow rate
Volume of water flowing through a device per unit time.
Pressure loss
Difference in pressure due to water flow between two specified points in a system or in part of a system.
It is expressed in pascals (Pa) according to ISO 80000–1, in kilopascals (kPa) or in bar.

Summary of the test method

Two CCM units, using identical test screens, are connected to the water mains, one upstream and one downstream of the filter under test.

Water at a flow rate of 10 l/min is passed through each CCM screen and the time required for each CCM to reach a predetermined pressure loss (0.5 bar) across its own screen is recorded.

The ratio between the two time periods, measured at the downstream and the upstream CCM units, is calculated. A ratio equal to or greater than five indicates that the filtration grade declared by the manufacturer is correct.

CCM structure and operation

Construction
The CCM device consists of two main parts (see Figure 1).

  1. Sampler (1)
    The sampler is the part of the CCM through which water used for testing flows. It includes the following:
    • Screen housing (3), capable of being opened and closed for cleaning and for easy replacement of the filtering screen (4);
    • Flow rate regulator (5), accurate to ±2%, limiting the flow rate to 10 l/min.
  2. Control unit (2)
    The control unit includes the following measuring instruments:
    • Pressure gauge (9) accurate to ±1%, measuring up to 10 bar;
    • Differential pressure gauge, digital or analog (10) accurate to ±1%;
    • Count up digital timer (6) with a resolution of 0.01 min, preferably starting automatically when the pressure reaches a pre-determined level;
    • Timer start switch (12);
    • Timer reset button (11). setting the timer back to zero;
    • Tubes (7 and 8) connecting the control unit to the sampler. Pressure tap construction shall be in accordance with ISO 9644.

Mode of operation

  1. Insert a "sealed" screen. same as that used for testing but that is covered and sealed by a thin plastic film into the screen housing. Apply an inlet pressure of (1+0.2) bar. Make certain that no water is emerging from the CCM outlet.
  2. Replace the "sealed" screen with a CCM test screen. having filtration grade equal to that declared by the manufacturer of the filter under test.
  3. Set the timer to zero by pressing the reset button.
  4. To begin the test, open the water inlet to the sampler and activate the timer start switch.
CCM device consists of two main parts: Sampler and Control unit.

Key

  • 1. sampler;
  • 2. control unit;
  • 3. screen housing;
  • 4. filtering screen;
  • 5. flow rate regulator;
  • 6. count up digital timer;
  • 7. pressure tube;
  • 8. pressure tube;
  • 9. pressure gauge;
  • 10. differential pressure gauge;
  • 11. timer reset button;
  • 12. timer start switch;
  • 13. water outflow;
  • 14. water inflow;
  • 15. low pressure;
  • 16. high pressure.

Figure 1 — CCM schematic construction

CCM test screen characteristics

The screens used in the CCM shall be made of 316 stainless steel and have plain weave of square mesh with the characteristics specified in Table 1.

Table 1 — CCM test filter screens characteristics
Aperture widtha
μm (micron)
Mesh counta
apertures/in
Wire diameter
mm
60 250 0.04
80 200 0.05
100 140 0.08
120 120 0.09
140 100 0.11
150 120 0.065
165 105 0.076
180 94 0.09
200 88 0.09
250 62 0.16
300 50 0.20
a In case of a discrepancy between Aperture width and Mesh count data. the Aperture width takes precedence.

Ccuracy of measurements

  • Pressure shall be measured with an accuracy of ±1%.
  • Pressure loss shall be measured with an accuracy of ±1%, using a differential pressure gauge.
  • Flow rate shall be measured with an accuracy of ±2%.
  • At the beginning of the test, the flow rate shall not deviate by more than ±2% from the required flow rate.
  • The difference in flow rate between the two CCM devices in the test system shall not exceed 4%.

Related articles: Filters filtration grade - test system layout and test procedure.

For more information please see ISO 18471:2015(en) Agricultural irrigation equipment — Filters — Verification of filtration grade.

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