Double Seal for Glass Lined Reactor Type 521/D & 521/D/B Mechanical Seals are designed for Top Entry Drives in Glass Lined Vessel. Compact Economical Cartridge Mechanical Seal for Glass Lined Vessel. These Seal specially designed for any mixed and pressurized liquid in Vessel with Top Entry Agitators where no leakage of Highly Acidic Process Gas OR Fluids to the Environment can be tolerated. Complete Pre-assembled Tested Unit ready for installation. These Seal are used for Exclusive Solid Seal Faces, Stationary Seats, thus Lowest Level of Seal face distortion when Expose to Compressive Load and Thermal Pressure.