The Solinst 408 Double Valve Pump is a pneumatically-driven, positive-displacement pump with a check valve at its base and another at its top, connected to the surface by separate drive and sample lines. During the drive phase, compressed gas sent down the drive line pushes the static water column downward, closing the bottom check valve and forcing water already in the pump chamber up through the top check valve to the sample line. Venting the drive-line pressure lets formation pressure reopen the bottom check valve and refill the chamber with fresh water, while the top check valve keeps the sample line from draining back down. Because the drive gas only ever contacts the drive-line water column — never the sample itself — the 408 is well suited to VOC-sensitive sampling at higher flow rates than a bladder pump can achieve.

Do you have everything you need? The 408 Double Valve Pump requires a separate compressed-gas source and control unit — such as Solinst's 464 Electronic Pump Control Unit — to drive its cycle; it does not operate on its own. Stainless-steel models are rated to 500 ft (150 m) below grade; PVC models to 100 ft (30 m), at operating pressures up to 250 psi. Replacement parts are available in the Solinst Waterloo System Parts & Accessories collection.