Packing, shaft Mechanical seals

Gaskets, turbine carbon packing, and mechanical seal parts can be purchased from local sources. Shafts, sleeves, cast parts can be purchased from... 

STUFFING BOX - That portion of the pump which houses the packing or mechanical seal. The stuffing box is usually referred to as the dry portion of the pump, and is located in back of the impeller and around the shaft. 

Type of shaft sealing required (simple gland packing or mechanical sealing)... 

Shaft packing too tight. Reduce packing tightness. If leak rate from packing unacceptable, replace packing with mechanical seal. 

Erosion is the wear of the pump internal parts by suspended solid particles contained in the fluid being pumped. The most affected parts are wear rings, shaft sleeves, packing, mechanical seal faces, lip seals, the pump casing and the impeller. 

Part Purpose Shaft sleeve Protects the shaft where it passes through the stuffing box. Usually used in pumps with packing but often eliminated if mechanical seals are employed. 

Shaft seal requirements and two common types of seals, packed stuffing boxes and simple mechanical seals, are described and discussed in this section. A packed box typically is used on slow- to moderate-speed machinery where a slight amount of leakage is permissible. A mechanical seal is used on centrifugal pumps or other type of fluid handling equipment where shaft sealing is critical. 

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. 

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.

This pump uses a closed impeller, mechanical seals, and is constructed of stainless steel 304L. The small power load of approximately 3.5 kW is supplied by an electric motor drive employing a horizontal shaft. The design casing pressure is sufficient to give a 30% safety factor above the total head required. Mechanical seals are preferred to a packed box arrangement due to their superior ability to contain the corrosive and toxic acid liquor. 

Charging manholes, agitator shafts shall be provided with gland packing of compatible materials or shall be water-cooled type to prevent escape of vapours. Mechanical seals may be fitted in case there is a possibility of escape of toxic or inflammable vapours. 

Whether jacketed constmction is required for keeping the liquid at optimmn temperature. Heating/coohng medimn to be used in the jacket Shaft sealing whether ordinary gland packing is okay or water-cooled glands or special mechanical seals are required (for toxic, corrosive and inflarmnable... 

Type of shaft sealing (gland packing/mechanical seal) required. 

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