Patent ID: 8268171

Claim:
A bottom control specimen filtering apparatus comprising: a container comprising: a cylinder body having a specimen receiving chamber in an upper portion thereof; a top cap having an orifice therein; a seal plug received in, and sealing said orifice; and a bottom cap; a piston rod disposed in a central hole at a lower end of the cylinder body; pistons tightly sleeved on projections of the piston rod and engaging the sidewall of said central hole; a drainage needle fixedly connected to a lower end of the piston rod by a screw thread; a clutch spring, an upper end of which is pressed against a portion of the cylinder body and a lower end of which is pressed against a flange of the drainage needle; and a double-layer filtering system composed of a first layer of filter screen and a second layer of filter screen, wherein a shaft of the first layer of filter screen penetrates through a middle hole of the second layer of filter screen and is fixed in a hole at the top of the piston rod, an upper surface of said first layer defining a lower end of said specimen receiving chamber.