The use of mass flow meters, rather than the traditional dry gas meters, allow for quicker leak checks and calibration checks during the sampling event.  The low-level meter is used for normal monitoring operation that requires sampling rates of up to 400 cc/min, and the high-level meter is used for applicatiions that require sampling rates of up to 4,000 cc/min, such as may be needed for a Relative Accuracy Test Audit.

In practical applications, the full sampling range of the unit is 50 cc/min to approximately 1,800 cc/min, depending primarily on the pressure drop created by the sorbent traps.  Each flow meter has an independent solenoid valve for control of sample flow rate during monitoring.  A third solenoid control valve is used to adjust the system vacuum during leak checks.  The mass flow meters and solenoid valves for both sample paths are mounted on a flow manifold made from a single block of Kynar (PVDF).