chamber 320 when a fluid sample is received in sample chamber 314 debris trap piston 318 is displaced downwardly relative to housing 302 to expand sample chamber 314 prior to such downward displacement of debris trap piston 318 however fluid flows through sample chamber 314 and passageway 322 of piston 318 into debris chamber 326 of debris trap piston 318 the fluid received in debris chamber 326 is prevented from escaping back into sample chamber 314 due to the relative cross sectional areas of passageway 322 and debris chamber 326 as well as the pressure maintained on debris chamber 326 from sample chamber 314 via passageway 322 an optional check valve not pictured may be disposed within passageway 322 if desired such a check valve would operate in the manner described above with reference to check valve 128 in fig2 b in this manner the fluid initially received into sample chamber 314 is trapped in debris chamber 326 debris chamber 326 thus permits this initially received fluid to be isolated from the fluid sample later received in sample chamber 314 debris trap piston 318 includes a magnetic locator 324 used as a reference to determine the level of displacement of debris trap piston 318 and thus the volume within sample chamber 314 after a sample has been obtained meter fluid chamber 320 initially contains a metering fluid such as a hydraulic fluid silicone oil or the like a flow restrictor.