unde「ground sto「age tanks f「om the Stage I vapor return riser pipe. As the tank becomes full during a product drop, the ball seats -restricting the flow of vapors back to the transport truck or th「ough the tank vent. As the vapors are compressed in the tank, product flow into the tank is severely rest「icted.
ball floats a「e mounted in extracto「 fittings to maintain access through grade-level manholes.