Elimination of Valve Packing Leaks by Accurate Pre-Stressing of the Packings

In all industries, leaking valve packings are a major maintenance issue, and in many cases, a major cause of pollution by liquid and volatile substances.  New data, installation procedures, and equipment have been developed to eliminate this problem.

Background

Design and installation of the valve packing must assure tightness along the valve stem while maintaining acceptable valve opening and closing forces.  Large compression forces and stresses on the packing and extensive number of packing rings can assure tightness but they lead to problems with valve closing and opening and overload or damage to electric and hydraulic valve systems.  Currently, there is not a uniform procedure and, in most cases, packings are inaccurately and unequally tightened using regular or torque wrenches.  

To balance the tightness and valve stem friction, small number of packing rings (5 to 7), low friction packing materials (Teflon, graphite fiber, etc.), and new pre-stressing and loading procedures are being used.  

Installation of Packing

The following steps and equipment are recommended:

Valve inspection and recording of dimensions

Review of valve packing design (number and materials of rings, compression, etc.)

Correction of number of rings and their material where needed

Installation of hydraulic cylinders (Figure 1)

Pre-deformation, hold time, unloading, final pre-stress (Figure 2)

Hand tightening of the packing bolt nuts

Removal of hydraulic cylinders

Valve test

Jonas, Inc. Equipment and Service

Jonas, Inc. supplies the hydraulic system for accurate pre-stressing of valve packings together with recommended stress and pressure sequence, and training and installation services.  New packing material characteristics (gasket factors) can be determined on special laboratory test rigs.    

Ordering Information  

Please specify the following:  valve types and sizes, packing flange bolt sizes, maximum number of packing flange bolts, type and number of packing rings, training (Yes/No), installation assistance (Yes/No; if yes, # of days)

Figure 1.  Installation of Hydraulic Cylinders on a 1-inch Valve

Figure 2.  Force vs. Displacement Sequence for Installation of Valve Packings