BS ISO 11057:2011 pdf free download – Air quality一Test method for filtration characterization of cleanable filter media.
5.6.7 Functionality tests for complete standard reference apparatus
5.6.7.1 Leak test
It is strongly advised to do a leak test, at least quarterly, as follows.
a) Use a plate of diameter 180 mm to seal the inlet of the horizontal clean gas tube (e.g. aluminium, 5 mm thick, mounted instead of the filter holder).
b) Put in a new absolute filter.
c) Remove the hose leading to the differential pressure transducer (to protect the transducer) and seal the tapping into the tube.
d) Switch on the pump to start the flow (set point 2 m3Ih).
e) The flow will decrease quickly to near 0 at full vacuum of the pump (when the mass flow controller opens up completely).
f) It should be possible to reach a flow <0,1 m3/h. g) If the flow does not reduce to this value, there is a leak which is influencing the measuring results. h) At the end of the test, break the vacuum by switching off the pump and slowly allow air back into the horizontal clean gas tube by the tapping to the differential pressure transducer. CAUTION — If an apparatus other than the standard reference apparatus is used, check whether the vacuum can be applied without damage. 5.6.7.2 Gradient of pressure drop curve This quick test shows whether all components and also the control and correction of the flow through the filter sample are working correctly, including the dispersion of the dust by the feeder. This short test should be done after doing the standard cleaning routine and after checking the transducers, the dust concentration and the feeder setting. The procedure is as follows. a) Use an expanded polytetrafluoroethylene (ePTFE) membrane on needle felt (not on woven material) as a test sample or a sample with a micro fibre surface, providing the formation of an undisturbed, homogeneous filter cake. b) Test dust (3.3) is Pural NF (report the lot number; values might differ slightly for different lots). c) Ensure that the dust concentration at the filter is 5 g/m3. d) Ensure that the filter face velocity is 2 rn/mm (calculated for actual conditions) at ambient temperature. e) Set the measuring interval to 1 s, cleaning valve opening time to 60 ms, and tank pressure to 0,5 MPa (over-pressure). f) Start the standard test procedure and perform at least one cycle up to 1 800 Pa. The pressure drop curve should be linear between 800 Pa and 1 800 Pa and should always show the same gradient at constant filtration velocity and dust concentration (see also 5.2.6). 5.6.7.3 Cleaning pulse signal The cleaning system is specified in 5.2.8 and the pressure pulse arriving at the filter sample is defined by the geometry of the horizontal clean gas tube, i.e. the clean gas tube, the blow tube and blow hole, the pressure tank and the valve design and opening time. The pressure pulse can change, e.g. if the function of the valve is deteriorating. Therefore its function should be tested periodically, at least annually. The test requires a perforated plate (see Figure A.3) and a measuring system with a quick-acting transducer and should be done by the manufacturer or the personnel performing the annual maintenance. The perforated plate is inserted into the filter holder instead of a test filter, the filter face velocity is set to the standard value of 2 m/mm and a pressure pulse is triggered with parameters set to standard values. 5.7 Step-by-step procedures of the standard test Step-by-step procedures of the standard test are as follows. a) Log the ambient conditions within the test room (atmospheric pressure, temperature, relative humidity). b) Set operating parameters of test apparatus: volume gas flow rates, dust feeder settings, cleaning set-point pressure, number of cleaning pulses, tank pressure, valve opening time. c) Check dust feeder contents. d) Check the dirty-gas dust concentration (see 5.2.2). e) Place the filter holder with the new test filter sample into the test apparatus. f) Weigh the absolute filter and mount into the absolute filter holder. g) Determine the initial pressure drop without dust feed. First switch on the vertical duct air flow manually and wait until the photometer is not showing any dust in the gas flow. Then start the flow through the sample and measure the initial pressure drop.