The straight back-water valves are made of a brass body, a brass cap, a brass nut and a brass connector. The straight back-water valve can connect other fittings or valves with male and female thread in straight direnction. it is usually installed on the backwater side of radiator,adjust the pressure difference between inter water and backwater and regulate the various heating loop resistance balance. The main size is D15, D20 and D32.