The 61Æ’STOP, available in either 2″ or 3″ full-flow models, maximizes flow rates and minimizes delivery times. The 2″ 61Æ’STOP requires a 4″ tank opening and minimum tank ullage (space from the top of the stored product to the inside top of the tank) of 8″ on the 61Æ’STOP-1000 Cylindrical Float model and a minimum ullage of 4″ on the 61Æ’STOP-2000 Float Arm model. The 61Æ’STOP-1000, with the cylindrical float, eliminates the need to position the valve to avoid tank walls or cross-bracing. The 61Æ’STOP-2000 with the float arm allows for increased usable storage capacity in the tank, and is well suited for small-capacity rectangular ASTs. The 3″ 61Æ’STOP requires a 6″ tank opening and incorporates a cylindrical float requiring 8″ of tank ullage space.