Mechanical Seal for Agitator and Pump
What is the use of Mechanical Seal (m seal)?
Mechanical Seal -Mechanical
seals are devices that are used to provide a seal at the point of entry or exit
of a rotating shaft.
it is used to prevent the
leakage of one high pressure fluid into a lower pressure fluid.
Earlier we used Gland packing
instead of mech seal, but due to gland rope is wear and leak again and again then
m seal invention for presentation of any leakage.
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| seal |
Mech seal has two faces, one
face is fixed with housing which is called stationery seal and other one face
is rotating face seal which is rotates with shaft.
Mechanical Seal Component
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| Seal Parts |
Rotating primary face – Fixed
to and rotates with the shaft and seals against the stationary primary sealing
element
Stationary primary face –
Fixed to the stationary housing of the pump, mixer or other equipment through
which the rotating shaft passes and seals against the rotating primary sealing
element
Mechanical loading devices –
Biases the primary sealing elements in contact to initiate sealing. These can
be a single spring, multiple springs, wave springs, or metal bellows.
Static and/or dynamic
secondary seals – Seal between the mechanical seal components and the equipment
shaft and housing that compensates for any shaft movement that may damage the
seal faces.
Drive mechanisms – Set screws
and drive pins are examples of drive mechanisms used to provide rotation to the
rotating primary seal face.
Material of mech seal
Carbide, silicon, tungsten,
carbon and Teflon PTFE, SS
Types of Mechanical Seal –
- Balanced seals.
- Unbalanced seals.
- Pusher seals.
- Non-pusher seals.
- Conventional seals.
- Cartridge seals.
Balanced seals –
Balanced seals reduce the seal
ring area (Ah) on which the hydraulic pressure of the liquid in the pump (Pp)
acts. By reducing the area, the net closing force is reduced. This allows for
better lubrication that results in lower heat generation, face wear, and power
consumption.
In the balanced seal, the
opening area or face area is same as the unbalanced seal, but the closing area
is maintained in proportion to the face area.
The pressure from both the
seal springs (Ps) and the hydraulic pressure of the liquid in the pump (Pp)
provide a compression force that keeps the seal faces closed. Balanced seals
reduce the seal ring area (Ah) on which the hydraulic pressure of the liquid in
the pump (Pp) acts.
Balanced seal is use for more
than 10kg/cm^2 pressure is maintaining.
Un balanced Mechanical Seal –
Unbalanced seal generates
multiple times higher hydraulic closing force generated by the actual pressure
that seals the two faces.
Though they are more stable
than the balanced ones, if the closing force on the seal faces crosses the
pressure limits, then it wears out the lubricating film which squeezes out, and
the dry seal fails due to heavy load.
Un balance pump is used for less pressure which is below 10kg/cm^2.
Compare between Balanced and Un balanced Seal –
Heat Generation
- More in unbalanced seals
- Less in balanced seals
Seal life
- More in balanced seals
- Less in unbalanced seals
- Vibration and stability
- Less stable and misaligned
- Liquid handling capacity
Unbalanced seals can handle
high capacities of high lubricity fluids
Balanced seals can handle high
capacities of poor lubricity fluids. They are best fit for light hydrocarbons
Seal face loading
- High in unbalanced
- Low in Balanced
Heat Generation
- Heat generation across the face is more in unbalanced seals
- Heat generation across the surface is low in balanced seals
Mechanical seal for Agitator In vessel /Reactor –
- Single Mechanical Seal
- Double Mechanical Seal
- Dry Mechanical Seal and
- Glass line reactor Seal
Single Mechanical Seal
Operating Range –
- Shaft Día: 25mm to 150mm
- Temperature: -30degree Celsius to 200 degree Celsius
- Speed: 400rpm
- Pressure: Full Vacuum to 30 bar
Material
Seal Ring Face – Carbon and
silicon
Seat Face TC and sic
Elastomer Viton, TTV and FEP
MOC- SS316
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| Fig- Single Seal |