Filter apparatus having a casing with improved structure for holding filter media

A filter apparatus comprising:

• a generally box-shaped casing comprising a first casing member having a concavity and a peripheral edge extending around the concavity, and a second casing member having a concavity and a peripheral edge extending around the concavity, the peripheral edges of said first and said casing members being connected to each other with a substantially uniform gap defined entirely therebetween and with the concavities of said casing members facing each other so as to collectively define the interior of the casing, and said casing having a suction port and an exhaust port each placing the interior of the casing in communication with the exterior of the casing;
• and
• a filter having the form of a bag and disposed in said casing, said filter comprising a first piece of filter medium and a second piece of filter medium, the entire peripheral edge of the first piece of filter medium being superposed with the entire peripheral edge of the second piece of filter medium, the superposed peripheral edges of said filter pieces being disposed and hermetically held in the entire gap between the peripheral edges of said first and said second casing members, and said first and said second filter pieces each having an open through-hole extending therethrough, the through-holes of said filter pieces being aligned and said filter pieces being joined to one another along portions thereof defining the peripheries of said through-holes, the aligned through-holes placing one portion of the interior of said casing defined to one side of the filter in communication with another portion of the interior of said casing defined to the other side of the filter, and the interior of the filter being in open communication with one of said ports.