AMS - Model 64337 -2 Inch Stainless Steel Multi-Stage Flap Valve Cap, Hex Quick Pin

The check flap on the top cap opens to allow excess air and water to escape through the four holes that are machined through the top cap. The venting action of the check flap and cap prevents pressure buildup while sampling. The check flap will also cover the machined holes while retrieving a sample to create a suction inside the sampler. The suction will help retain the collected sample.