Shafts, rotating, sealing packing seal

As the pump shaft rotates, the shaft packing rotates with it due to friction. (In more complex mechanical seals, the shaft-packing element is secured to the rotating shaft by Allen screws.) There is also friction between the spring. 

Main Seal Body The term seal body makes reference to all rotating pai ts on a pusher seal, excluding shaft packing and seal ring. In many cases it is the chief reason to avoid a particular design for a particular seiwice. 

Mechanical seals offer a more reliable seal than compressed packing seals. Because the spring in a mechanical seal exerts a constant pressure on the seal ring, it automatically adjusts for wear at the faces. Thus, the need for manual adjustment is eliminated. Additionally, because the bearing surface is between the rotating and stationary components of the seal, the shaft or shaft sleeve does not become worn. Although the seal will eventually wear out and need replacing, the shaft will not experience wear. 

Figure 7.13. Types of seals for pump shafts, (a) Packed stuffing box the sealing liquid may be from the pump discharge or from an independent source, (b) Water cooled stuffing box. (c) Internal assembly mechanical seal the rotating and fixed surfaces are held together by the pressure of the pump liquid which also serves as lubricant a slight leakage occurs, (d) Double mechanical seal with independent sealing liquid for handling toxic or inflammable liquids.

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