Comparison : Item # ROPD3.1, 4-1/4# OPD Valve with 3.1" Dip Tube
Item # ROPD3.6, 11# OPD Compact Cylinder Valve with 3.6" Dip Tube
Item # ROPD4.0, 20# OPD Valve with 4" Dip Tube
Item # ROPD4.7, 30# OPD Compact Cylinder Valve with 4.7" Dip Tube
Item # ROPD6.4, 40# OPD Compact Cylinder Valve with 6.4" Dip Tube