Assembly
Assembly is a very important step to achieve the desired tightness and function of stuffing box stem seals.
During assembly, a good seating of the packing has to first be reached. 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 stated: radial stress) has to be maintained during every state of operation.
On the other side radial force, / stress induces friction between the stem and packing. For proper function of a valve, limited friction is essential.
As a consequence, tightening of stuffing box packings during assembly is a kind of optimization task: Regarding tightness the assembly stress value has to be high; regarding friction is has to be minimized.
Reliable assembly of stuffing box packings is challenging; thorough preparation is needed as well as skilled personnel.
The tightening procedure has to meet the performance demands. If the demands are high the TEMES stb.ctrl procedure is an option to consider.