55.Explain the procedure of alignment of a rotating equipment? What is reverse and soft foot alignment?

Two rotating shaft shall be aligned  such that the shear forces and bending moments at the coupling are zero.

Final alignment of rotors are obtained by adjusting the bearings ( for turbine rotors) and by adjusting the motor for Pumps, fans, etc to give parallelism and concentricity at each pair of couplings.

The alignment is carried out by measuring the face gaps and periphery errors between couplings.

Gap measurements, using suitable gauges, are taken at the top, bottom and two side positions and a repeat set taken with both shafts rotated through 180 deg. The average of the two sets indicates the true parallelism of the coupling faces, eliminating any errors due to out of truth between couplings and shaft.

Concentricity is checked by measuring between the peripheries of the two couplings, using either dial indicators or feeler gauges, to a finger attached to one of the coupling. To eliminate coupling errors, both shafts are turned together and readings taken at the top, bottom and two side positions.

Calculations using ratios and similar triangles, taking account of shaft length, distance between bearings and coupling diameter, determine the adjustment required at the bearings to obtain shaft alignment.

With solidly –coupled shafts, it is usual to work to very close tolerances of the order of plus/minus 0.025 mm.