The diameter of inner shell is larger than diameter of shaft. Stuffing Box: Stuffing Box has two shells.
Seaing arrangement does not allow vapours to leak out of vessel, along the rotating shaft. Type of Seal: Stuffing Box or Mechanical Seal: A seaing arrangement is provided in a closed vessel, along agitator shaft at the top. Lower fixed bearing is a non rotating bearing, made of a sleeve of softer metal or plastic material. To avoid this a bottom bearing is provided. The lateral movement of impeller at the bottom of the shaft, tries to bend the shaft, if shaft is long (more than 3 meters). Overhang of shaft and lower fixed bearing: The shaft is supported at the top end by bearing housing assembly. Power required for agitation: Power depends on diameter of impeller, revolutions of agitator shaft, power number of impeller, number of impellers, density, content of solids and viscocity of liquid. Baffles and coil reduce effective diameter of the vessel. Coils are provided in some vessels, for heating or cooling. For last 4 (radial flow), no baffles are provided. Diameter of impeller is generally 1/3rd the diameter of the tank forĭiameter of impeller is generally 80% of the diameter of the tank forīaffles / Coils: Generally 4 baffles are provided in a vertical cylindical vessel for good mixing in case of first 6 (axial flow) impellers. All other impellers are of fabricated construction and can be either Bolted or Welded type.ĭiameter of Impeller: Diameter of impeller depends on diameter of tank. Impellers may be one piece or split into two or many pieces, bolted together. Hub is installed on the shaft by shaft key and grub screw. Main parts of impeller are hub and blades. Marine Propeller, Axial Flow Turbine, Turbo Propeller, Disc Blade turbine, Flat Blade Turbine, Backward turned turbine, Paddle, Anchor, Anchor/Paddle or Gate. Impellers: There can be following simple Impellers. However, agitator is also installed in vertical rectangular tank, in water and waste water treatment tanks. Shape and size of tank: Vertical cylindrical vessel is the best type for installing an agitator. Agitator is located off-center if some part of vessel is occupied by internal coil or some other internal. Location of agitator in the equipment: Generally agitator is centrally located for better flow pattern. When both patterns of circulation are required, radual flow impeller is installed at the bottom of agitator shaft, while radial flow impeller is installed at the center of agitator shaft. When the contents are to be mixed, radial circulation is prefered. When a vessel is heated or cooled by coil or jacket, axial flow is prefered. Agitator can also mounted horizontally from side of a tank, called side entering agitator, for very large diameter storage tanks. This is the normal practice for mounting an agitator in small and medium size tanks.
Type of Agitator: Generally agitator is mounted vertically at the top of the tank. Degree of agitation increases with increase in number of revolutions of agitator and increase in impeller diameter. For Mild mixing, time required for total mixing can be few hours. For Moderate mixing, time required for total mixing can be few minutes.
For Vigourous mixing, time required for total mixing can be few seconds. Type of Agitation: Agitation can be Vigourous, Moderate or Mild. For Agitators / Mixers, factors to be considered for design are
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