A sampling apparatus for use with a sample analyzer comprises a sample probe insertable into a process
stream, and an extraction cylinder including a variable volume chamber and a
piston movable by an
actuator back and forth in the cylinder to increase and decrease the volume of the variable volume chamber. A
sampling valve is connected between the extraction cylinder and the sample probe, with a sample line connecting the
sampling valve to the sample probe, and the variable volume chamber having a capacity substantially greater than the combined volumes of the sample probe,
sampling valve and sample line. A filter
assembly is interposed between the sample probe and sampling valve for filtering undesired substances from the fresh sample prior to the fresh sample reaching the sampling valve, and a controller is provided for controlling the
actuator and the sampling valve, first to move the
piston at a first rate to increase the variable volume chamber sufficiently to draw fresh sample from the process
stream and past the sampling valve, then to operate the sampling valve for injecting fresh sample into the sample analyzer, and thereafter to move the
piston at a second rate greater than the first rate to decrease the variable volume chamber to flush excess sample back into the process
stream and clean the filter of undesired substances filtered from the fresh sample.