Assembly

Assembly is a very important step to achieve tightness and function of stuffing box stem seals.

During assembly, a good seating of the packing has to be reached, first. This is realized by plastic deformation of the packing rings. Existing gaps (between stem and packing / packing and housing / between the rings) have to be filled and internal leakage paths have to be closed. This process is accelerated with increased load.

After this pre-deformation a given assembly stress value (tightening torque) has to be applied. Usually, the packing is compressed axially using a gland and bolts; the main tightening surfaces are between stem and packing / packing and housing. Therefore, regarding tightness a sufficient radial force (better: radial stress) has to be maintained during every state of operation.

On the other side radial force / stress induces friction between stem and packing. Regarding function of a valve limited friction is essential.

As a consequence, tightening of stuffing box packings during assembly is a kind of an optimization task: Regarding tightness the assembly stress value has to be high; regarding friction is has to be minimized.
 

assembly principle for a packing

 
Reliable assembly of stuffing box packings is challenging; thorough preparation is needed as well as skilled personnel.
 

stuffing box packings: friction versus tightness

The tightening procedure has to meet the demands. If the demands are high the amtec TEMES stb.ctrl procedure is an option to consider.