Design a helical spring for a spring loaded safety valve for the following conditions : Operating pressure = 1 N/mm? Maximum pressure when the valve blows off freely = 1.075 N/mm2? Maximum lift of the valve when the pressure is 1.075 N/mm? = 6 mm Diameter of valve seat = 100 mm Maximum shear stress 400 MPa %3D Modulus of rigidity 86 kN/mm? Spring index = 5.5 [Ans. d = 17.2 mm ; D= 94.6 mm ; n = 12]