Definition Of Mechanical Seal
Seals intend to prevent media( water or oil ) used by machine leaking to external enviroment. That is the reason that mechanical seals can help to stop enviroment contamination. And save power through efficient operation.
A seal is simply a method of containing, such as pumps or agitators. Where rotate shaft pass through pump housing, by occasionally.
Mechanical Seal Types
There are multiple design structure to choose for mechanical seal configuration. Knowing mechanical seal basics and working principle will assist user to select proper seal type for application.
Pusher seals contain secondary seals, which move axially along shaft or sleeve to accommodate wear and assist in misalignment of shaft by spring compression, to keep contact of seal faces.
The advantages are those mechanical seal are cheap and have a wide range of sizes and configuration.
Non pusher seals and Bellow types
No pusher seals have no secondary seal, must move along shaft or sleeve to keep seal faces contact. In non pusher seals, secondary seals are in static state, even pumps on running. The secondary seal is not required to make up travel, when rotary seal and stationary seal wear. Primary seal faces are accommodated by elastomer bellows or welded metal. That move can assist in compression of rotary to static seal faces.
Advantages: It doesn’t need secondary seal, and it can also handle high temperature and low temperature application. Elastomer bellows are commonly used for water.
Disadvantages: The cost of metal bellow seals is very expensive.
Mechanical seals can be premounted on sleeve. Those are installed onto shaft or sleeve. It can provide single, double, tandem configuration. The best pump user will fully consider cartridge mechanical seals.
Advantages: The seal configuration eliminates requirements of sealing setting measurement. Setting a cartridge seals will be easier. Lower maintaince cost and less seal setting errors.
Disadvantage: It is the higher cost, plus in some cases they will not fit into existing stuffing box/seal housings.
Design & Material Seleciton
Design and material is very important for mechanical seal basics.
A basic mechanical seal contains 3 sealing point. Static part of sealing is fitted onto pump houising through static seal. This can be sealed by o ring or gasket clamp between pump housing.
Rotary part of sealing is typically fitted onto shaft by o ring. The sealing point can be regard as static, because the part of sealing rotate with shaft.
The selection of primary sealing material can also have effect on seal life. Chemical and process is just a consideration. Harder material is more resist abrasive.
Thermal conductivity of material can dissipate heat away from seal face. Then it can promote seal life. Material roughness can also be a primary role in mechanical seal life.
Pls note that many seal failure result from exceed chemical compatibility, temperature limits, pressure, failed secondary seal. Metal parts must be compatible to avoid corrosion. And spring and other hardware must hold up in operation.
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