|Since 1966 bacteriologists have come to respect the
May impingers for the separation of particles according
to their deposition sites in the respiratory system. The
fractions are collected gently into liquid where clumps
separate into viable units. There is little danger of
sample overload and sub-samples permit the use of a
variety of culture methods.
The original designs involved complex glass blowing, were difficult to clean and to reproduce accurately. The 20 l/min size is designed to produce particle fractions (> 10 µm, 10-4 µm, < 4 µm) that are closest to those likely to be agreed as international standards.
The Burkard version closely follows May's intermediate (20 l/min) size, accurately produced in anodised aluminium alloy (or stainless steel). Airtightness is ensured by vertical compression, releasing this allows the sampler to be dismantled for removal of the catch, and for cleaning. It can then be fitted and re-assembled before heat sterilisation and operation. The flow is controlled by a critical orifice built into the third stage. To ensure this accurate flow the vacuum pump must be capable of maintaining a pressure difference of at least 180 mm (7inches) of mercury. A 'stagnation-point shield' is provided to improve aspiration efficiency in moving air. To maintain the designed depth of collection fluid in the machined chambers it is recommended that 6 ml be added to each stage. (Not 4 ml as originally described).
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© Burkard Manufacturing Co. Ltd., 7 January, 2001