Pressure Actuated, High-Flow Unloaders from AR Pumps. VRT Series Unloaders (models AL606 and AL607) feature brass construction and stainless steel internals. Model AL638 is 316 Stainless steel construction. All models shown are designed to bypass at near zero pressure and operate at the maximum pressures shown. Ports are 3/8" FPT inlet, outlet and bypass and 1/4" FPT gauge port. Rated to 190° F.