Part #ws15X10078, Water Softener Bypass Valve / 12.60 x 5.80 x 5.50. This bypass valve (part number WS15X10078) is for water softeners. Bypass valve WS15X10078 allows you to stop the flow of water into the water softener while still allowing water to flow to your home's faucets. Turn off the water supply and disconnec... - Part #ws15X10078, Water Softener Bypass Valve / 12.60 x 5.80 x 5.50.