3. Design a helical spring for a spring loaded safety valve for the following conditions: Operating pressure - 1 N/mm² Maximum pressure when the valve blows off freely 1.075 N/mm² Maximum lift of the valve when the pressure is 1.075 N/mm² Diameter of valve seat Maximum shear stress Modulus of rigidity Spring index 6 mm 100 mm 400 MPa - 86 kN/mm² 5.5 [Ans. d 17.2 mm; D-94.6 mm;n-121