The necessary application data must be obtained to ensure normal improvement.These data items include: ·power(HP or kW)and speed(minimum,maximum and standard operation); ·shaft end details of active and driven equipment; ·B.S.E.(shaft end face spacing,also known as shaft spacing); ·predicted thermal expansion(volume and direction of expansion); ·upper limit requirements for angular offset(common requirements for high-performance couplings); ·service object(pipeline compressor,ethylene unit); ·whether the coupling needs to comply with the api-671 specification--for turbine equipment,it must; ·environment(saline spray,chlorine water,hydrogen sulfide). To ensure smooth completion of the improvement,the coupling designer needs to know the weight of each half of the coupling and CG(center of gravity)position so that the suspension torque is consistent.By matching such data with the proposed diaphragm coupling,the lateral critical velocity of the unit will not be affected.In order to ensure successful improvement,some of the major original manufacturers of turbocompressors developed some principles based on speed.·if the speed is 3600 RPM lower,each half of the weight and center of gravity of the new coupling should be within 20%of the existing coupling. ·when the rotation speed is between 3600 and 6000 RPM,each half of the weight and the position of the center of gravity should be within 15%.·when the rotation speed exceeds 6000 RPM,each half of the weight and the position of the center of gravity should be within 10%. In addition,it should be consistent with the torsional stiffness or Kt of the existing coupling to prevent the critical torsional speed of the unit from changing.Generally speaking,the two-part unit or transmission device directly connected to the slave equipment is not very sensitive to the Kt change of the coupling,but if there is a gearbox or a second or third rotor,this change will have a significant impact.