An Experimental-Numerical Procedure for Stuffing Box Packing Characterization and Leak Tests

Abstract

The sealing of valve stems is ensured by the traditional systems of packed stuffing boxes. The performance of this type of sealing system, which is also used in rotating equipment, is dependent on the radial contact pressures generated by the packing axial compression. The mechanical behavior of a packing seal is characterized by the transmission ratio of the radial stress over the axial stress known as the lateral pressure coefficient, which is one of the required parameters used to select packing seals. However, the modeling of the packed stuffing box requires the knowledge of other packing seal mechanical characteristics such as compression modulus and Poisson’s ratio. In this paper, the mechanical characteristics of packing seals are obtained using a hybrid experimental-numerical procedure. The experimental study is carried out on an instrumented stuffing box packing test bench. The tests results of the experiments are coupled to the ones obtained by a finite element simulation of the test rig to determine the packing seal mechanical characteristics. Two packing types are used: one based on Teflon and the other one based on flexible graphite. In addition, leak rates are measured for different axial compressive stresses and gas pressures in order to estimate the tightness performance of such seals.