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What are Mechanical Seals in Centrifugal Pumps and why they are Required?
In the centrifugal pumps the rotor, on which the impeller is mounted, revolves in the stationary housing of the pump and there is minor gap between the two. The centrifugal pump pumps a variety of fluids and sometimes these fluids can be highly hazardous to the humans and also the environment.
The most effective method of preventing the leakage of the fluid from the centrifugal pump to the external surroundings is using the mechanical seals. The mechanical seals help sealing the rotating part of the shaft against the stationary part of the pump housing. Thus the mechanical seals are the devices that form the packing between the rotor and the stationary part of the centrifugal pumps to prevent the leakage of the fluid being pumped by the pump. There are two main parts of the mechanical seals: one is the stationary part, which is connected to the pump housing and the other is the rotating part which is connected to the rotating shaft.
Prior to the mechanical seals, the compression packing like gland packing were used as the sealants though they are still being used in number of applications. The mechanical seals are especially used in the process applications where the pumps handle hazardous chemicals like HCL, sulfuric acid, etc. to meet the safety and the environmental standards as per the federal regulations.
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Advantages of Mechanical Seals over Glands (Compression Packing)
The advantages of mechanical seals over compression packing or glands are:
1) Mechanical seals ensures almost zero or very little (as per the regulations) leakage of the fluid from the pump casing to the surroundings.
2) The mechanical seals can sustain high pressures of the fluids and highly corrosive fluids. There is always some leakage from the compressible packing and sometimes they tend to fail under the deteriorating effects of the chemicals, but such problems do not occur with the mechanical seals.
3) There is no friction between the moving parts of the mechanical seal so there is no extra power consumption by the pump.
4) There is no wearing of the shaft or the sleeve on which the mechanical seal is mounted.
5) The mechanical seals are robust components so they require very less maintenance.
6) The mechanical seals are now available in wide variety of designs suitable for number of applications.
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Parts of the Mechanical Seal
The main parts of the mechanical seals are (please refer the figure above):
1) Rotating and fixed face: The rotating and the fixed faces are the two vital parts of the mechanical seals. The rotating face is connected to the rotating shaft while the fixed face is connected to the pump housing.
2) Secondary sealants: Between the two faces of the mechanical seal the secondary seals, known as shaft and insert mountings, like O-rings, wedges and V-rings are inserted.
3) The hardware of the mechanical seals like gland and compression ring, springs, pins, bellows etc.
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