In a hot water vacuum extraction machine comprising:
- an outer casing of electrical and thermal insulation material having a bottom wall, a top wall and generally vertical sidewalls, a circular opening within said top wall, a removable tubular recovery tank positioned within said circular opening within said top wall, a dome overlying the circular opening within said casing top wall, a hydropneumatic water filtration system within said recovery tank including a mixing tube structure extending upwardly from and supported by a recovery tank bottom wall including an aqua filtration tube coupled to a dome inlet duct within said dome at one end and extending coaxially within a larger diameter water entraining tube, said water entraining tube being closed at its bottom and spaced axially from an open lower end of said aqua filtration tube, at least one water inlet port within said water entraining tube opening to the interior of said recovery tank and being open to an annular space between said concentric water entraining tube and said aqua filtration tube, such that liquid filling the recovery tank above the level of said at least one water inlet port is aspirated by return fluid moving through contaminants within said return fluid entering said annular space in the vicinity of said water inlet port to cause contaminants within said return flow to be entrained by said water for primary filtration of said return flow stream, a hollow riser tube extending upwardly from the bottom of said recovery tank and being open at a level above the level of water within said recovery tank, and means for applying vacuum pressure to said riser tube at the bottom of said recovery tank to effect filtering of the return fluid stream, the improvement comprising:
- means within said recovery tank and interposed between the bottom wall of said recovery tank and said outer casing defining an air filter chamber, means for sealing the bottom of the riser tube to said tank bottom wall and open to said air filter chamber, means within said recovery tank bottom wall and said case for defining a sealed outlet for said return fluid stream and being open to said source of vacuum pressure, and a secondary filter holder assembly mounted within said air filter chamber and comprising a perforate filter holder supporting internally an open pore filter element, whereby said secondary air filter may remove contaminants of submicron size to render the air discharging from the case virtually contaminant free.