Ball-type Check Valves have the least expensive form of construction, but as the Ball is not guided there is a tendency for leakage to occur. Although manufacturers claim their check valves are leak-free in one direction of flow and allow free flow in the reverse direction, a tiny scratch, wear mark ,or imperfection on the poppet or scat will permit some leakage. Soft-seated check valves use Delrin or similar polymer material for the waling and 100% scaling is possible but at the expense of valve life. However, they are no generally suitable for pressures above 200 bar or temperatures above 35