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Performance Tests of Automatic Flushing Microirrigation Filters

Performance tests for automatic flushing strainer-type filters and disc filters used in agricultural irrigation systems.

1. General

The tests and the requirements given in this article and filters performance tests after long term simulated use apply to filters whose design or manner of operation are in accordance with the concept inferred by the test process described in the applicable clause.

The concepts of flushing cycle and flushing duration may not apply to all filters (for example: automatic continuous-flushing filters).

In such cases, the test procedure shall be adapted to the specific filter design and the declaration in the manufacturer's literature. However, it is important to ensure that the volume of flushing water shall not exceed that declared by the manufacturer by more than 7%.

A filter that does not contain an integral control system shall be tested together with a control systemindicated in the manufacturer's literature, as a combined system. In this case, the results of the test will apply only to the combination of the tested filter and the specific control system.

2. Volume of flushing water and duration of flushing

  1. Test at specific operating pressures
    Connect the filter as described in the manufacturer's instructions to a test assembly, simulating field installation. Ensure that the test assembly is capable of supplying at least twice the maximum flushing volume at the nominal pressure, as declared by the manufacturer.
    Attach a collection vessel to the flushing opening of the filter for collecting the flush water. Set the pressure at the filter inlet to the minimum flushing pressure and initiate a flushing cycle manually.
    Measure the volume of the collected flushing water and the time from the moment the flush valve begins to open to the time it closes.
    Repeat the test at the nominal pressure.
    The following requirements shall be met:
    • The volume of water measured in each of the tests shall not exceed the volume of flushing water declared by the manufacturer by more than 7%;
    • The duration of flushing measured shall not deviate from the flushing duration declared by the manufacturer by more than ± 15%.
  2. Test at the minimum flow rate
    Connect the filter as described in test at specific operating pressures. Ensure that the test assembly is capable of supplying at least the maximum flow rate recommended at a pressure differential equal to the safe maximum pressure drop.
    Attach a collection vessel to the flushing outlet of the filter for collecting the flush water. Operate the filter at a flow rate equal to the minimum recommended flow rate, with the pressure at the filter set to the critical pressure drop before failure. Manually activate the flushing mechanism twice.
    At each activation measure the volume of flush water and the time from the moment the flush valve begins to open to the time it closes.
    The following requirements shall be met:
    • The flushing mechanism shall operate satisfactorily (the flushing process is completed);
    • The volume of water measured in each of the tests shall not exceed the volume of flushing water declared by the manufacturer by more than 7%;
    • The duration of flushing measured shall not deviate from the flushing duration declared by the manufacturer by more than ± 15%.

3. Operation of the flushing control mechanism

  1. Mechanism activated by pressure differential sensor
    Disconnect the "low" pressure connection of the pressure differential sensor and connect it to an external pressure source. Leave the “high” pressure connection as connected for regular filter operation.
    Apply a pressure equal to the minimum filtering pressure at the filter inlet and at the external pressure source. Gradually reduce the pressure at the external pressure source until the flushing operation is performed.
    Repeat the test once with a filter inlet pressure at midrange between the minimum filtering pressure and the nominal pressure, and once more with a filter inlet pressure equal to the nominal pressure.
    The pressure differential (the filter inlet pressure minus the external source pressure) that causes flushing shall not deviate from the pressure differential declared by the manufacturer by more than ± 10%.
  2. Mechanism activated by duration of operation
    Perform the test three times, each time presetting the flushing control mechanism to a different time interval – short, long and intermediate – within the range of adjustment declared by the manufacturer.
    Operate the filter with an inlet pressure equal to the minimum filtering pressure. Measure the time interval between one activation and the next one.
    Repeat the tests with a filter inlet pressure equal to the nominal pressure.
    The time interval between the two activations shall not deviate from the preset time interval by more than ± 5%.
  3. Mechanism activated by volume of filtered water
    Perform the test twice, each time presetting the flushing control mechanism to a different volume of water within the range specified by the manufacturer. Select one volume from the lower 20% of the range and the second volume from the upper 20% of it.
    Operate the filter and measure the volume of water flowing through the filter up to activation of the automatic flushing control mechanism.
    The measured volume of water flowing through the filter shall not deviate from the preset quantity of water by more than ± 10%.
  4. Mechanism activated by another physical quantity
    Connect the filter to a water source and make all the adjustments necessary in accordance with the manufacturer’s instructions.
    Maintain the pressure at the inlet to the filter at the minimum filtering pressure.
    If the flushing control mechanism is adjustable conduct the test three times, with the flushing control mechanism preset differently each time, to the lowest, the highest and the mid-range setting, respectively.
    Otherwise, conduct the test only once.
    Operate the filter according to the manufacturer’s instructions until three flushing cycles have been completed.
    Measure the value of the activating physical quantity at the initiation of each flushing cycle.
    Repeat the entire process with the pressure at the inlet of the filter readjusted to the nominal pressure.
    The following requirements shall be met:
    • The flushing cycle shall be initiated and shall proceed as prescribed by the manufacturer;
    • The value of the activating physical quantity at the initiation of any flushing cycle shall not deviate by more than ± 10% from the preset value for an adjustable mechanism, or by more than ± 10% of the value declared by the manufacturer for a non-adjustable mechanism.

4. Operation of the protective mechanism

In filters equipped with a protective mechanism to prevent repeated flushing, test the mechanism as described below.

Operate the filter at an inlet pressure equal to the minimum filtering pressure. Perform three consecutive flushings manually.

The filter shall flush satisfactorily.

Continue to operate the flushing control mechanism manually several times until the protective mechanism stops the flushing cycle, or create by artificial means the conditions declared by the manufacturer which will activate the protective mechanism.

The number of flushings or (depending on the type of control mechanism) the time that elapsed, until activation of the protective mechanism, shall not deviate by more than ± 10% from the manufacturer’s declaration.

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