Maxitrol 1-1/2in straight flow thru regulator rv81-1 1/2, up to 4,500,000 btu maxitrol’s original straight-thru-flow design meet your needs for high capacities at low inlet pressures. Models are designed for 1/2 psi rate pressure under the ansi standard for gas pressure regulators. They are main burner only, non-lockup type. Use only where downstream controls can operate at line pressure.