The vacuum viscoseal with buffered stuffing box is the standard seal for WITTE POLY pumps. It is a combination of a dynamic (viscoseal) and a static (stuffing box) sealing system. The polymer flow back to the suction side is adjusted by a needle valve. The fluid barrier ensures that no air from the atmosphere gets in the pump/reactor. There is a buffered and heated stuffing box for back-up. To prevent failure/destruction of the packings, it is strongly recommended to heat the area of the stuffing box.