The operation of SV Control level controller is based on Archimedes principal. In The level controller the body immersed is called a displacer which is Suspended from a torsional measuring spring called torque tube. The Displacement for full level range varies from zero (displacer hanging free) To 100% at the top range. The displacer always weighs more than the Upward buoyant force which may be developed by the liquid in which it Is submerged. Although the displacer rises and falls with level change Its movement is substantially less than actual level movement. The difference in movement between displacer & Liquid level is dependent On the cross sectional area of the displacer, the specific of the liquid and the stiffness of the Torque tube. Displacer are usually of cylindrical shape, having constant cross sectional area so that for each equal Increment of Submersion depth, an equal increment of buoyancy change will result, Yielding the desired linear Or proportional relationship. The torque tube is designed to twist a specific amount for each increment of buoyancy Change To be insensitive to pressure changes on the vessel. The degree of rotation of inner end of torque tube Will be in linear relation to the degree of Buoyancy. The rotation of shift is converted to proportional pneumatic output.