Part Number: 8.705-039.0 Cross Reference Part Number(s): 87050390 This 8.705-039.0 Backflow Preventer protects water supply from chemical backflow and will not allow spike pressure to push chemicals into supply line. This back flow preventer is often required by many city and state regulations on equipment such as pressure washers. This back flow preventing check valve has a machined brass housing and plastic diaphragm check. Installs easily by threading into garden hose inlet on pressure washer.