The McAlpine ARB-1 is a 4"/110mm Anti Back-Flow and Rodent Barrier Valve that is designed to prevent sewage or wastewater from flowing back into a building's plumbing system, which could lead to contamination and health hazards. This valve is particularly useful for properties that are located in areas with a high risk of flooding or where there is a risk of sewage or wastewater backing up into the plumbing system. The valve operates by allowing sewage or wastewater to flow out of the building's plumbing system, but preventing it from flowing back in.