The mechanical seal is used in a pump, mixer and other mechanical engineering scenarios to contain the fluid within a vessel where a shaft rotates through a stationary (or rotating) housing.
Why is mechanical seal important in this situation? It is because the rotating shaft has to move in a wet environment, but there should not be the leakage of pressurized fluid. Hence, the role of a seal is quite critical.
Does it mean the seal stops the leakage completely? Well, on the practical grounds yes because there is no ‘visible leakage’.
There is a little leakage as the fluid vapors get released into the atmosphere from the faces of the seal, though. Since the quantity is hardly quantifiable, the seals are considered leak proof.
The seals do not damage pump sleeve or shaft.
Due to inboard springs that get adjusted as the seal faces wear, it is not required to do daily maintenance.
Mechanical seals cause less power consumption than gland packing because of the lightly loaded faces.
In mechanical seals, the lubricant doesn’t get washed out. Therefore, bearing contamination gets avoided in normal operational conditions.
Plant equipment remains corrosion free.
Relatively less maintenance and cleaning are required. It makes mechanical seals cost-effective.
Oil seals prevent accumulation of dirt in the machine.
Oil seals close off the space between stationary and moving components in the mechanical equipment. It saves the lubricant from escaping through the equipment and ensures smooth operation of the machine.
Oil seals are called rotary shaft seal or radial lip also.
Oil seals prevent seeping of potentially hazardous contaminants like dirt or fluid in the running machine
These seals safeguard mixing of two things like oil and water
In the high-intensity work environment, oil seals play a vital role
Oil seals are long-lasting and sturdy
Oil seals can work relentlessly if the preventive and corrective maintenance is in place
Low wear and tear
Types Of Component Mechanical Seals
Seals and gaskets are sometimes custom-made to service unique applications, but we can group most seals that prevent leakage at the interface of a moving part and a stationary part into eight main types of component mechanical seals.
Wave Spring Mechanical Seals: Principally used for liquids of high viscosity, wave spring mechanical seals are popular for pharmaceutical, dairy, brewery and food processing applications. They are often fitted to the shaft with grub screws and in the case of high viscosity media would also have stationaries with anti-rotation pins. Some designs are specially constructed to work in shallow, confined seal housings.
Water Pump Seals: Because water is such a poor lubricant of seal faces, it is critical that water pump seals use excellent materials for applications such as shower pumps, irrigation, heating systems, swimming pools and spas.
Bellows Mechanical Seals: Compact, versatile, extremely reliable seals suitable for a wide range of applications. Available with either O Ring Mounted or Boot mounted Stationaries in DIN and Non-Din sizes. Recommended for media containing solids and are widely used in Pumps, mixers, compressors etc.
Diaphragm Seals: Featuring parallel springs, diaphragm seals are used in very diverse applications including agitators, compressors, mixers, pumps and other rotary shaft equipment. . The diaphragm in the rotary head rotary seals on the shaft so they are not affected by rotational direction.
Balanced Diaphragm Seals: Similar to Diaphragm seals but are also hydraulically balanced to reduce heat and friction at the seal interface, an innovative patented design protects against seal failure in applications where thin metal drive components are prone to cut into the retainer.
Conical Mechanical Seals: This is an extremely versatile and popular mechanical seal. Available in a wide range of materials to suit a variety of environments, they are robust and durable. However these seals are rotation dependent and come with either left hand or right hand springs.
Parallel Mechanical Seals: Parallel seals are a heavy duty single spring seal. They can use different methods of providing the face to the seal and can be supplied with either left- or right-hand wound springs. A good general-purpose seal, they are used in marine pumps, waste-water, pulp and paper and textile applications as well as refrigeration compressors.
Multi Spring Seals: Proven effective design, PTFE wedge styles are often used in chemical the chemical industry for arduous applications such as corrosive process fluids.
What is a Double Seal
Double (or dual) mechanical seals are designed to ensure maximum sealing safety. These seals virtually eliminate leakage of the fluid or gas being handled in pumps or mixers.
Double seals provide a level of safety/zero emissions compliance not possible with single seals. This is essential when pumping or mixing a dangerous or toxic substance.
Double seals are a must-have for certain applications in many countries
These seals are increasingly used by companies to meet specific environmental goals or emissions requirements.
A properly installed double seal also allows for near complete control over the seal operating environment and fluid film over the seal faces. This factor alone can greatly maximize seal life.
A double mechanical seal has two primary seals with a barrier or buffer fluid area in between. Each primary seal typically consists of a softer, narrower stationary face accompanied by a harder, wider rotating face. This arrangement enables the softer seal to wear while maintaining the integrity of the harder faced seal during service.
Pump and seal manufacturers recommend double seals for a variety of reasons:
Prevent a hazardous product from reaching the atmosphere/polluting the environment
Avoid leakage of an expensive process fluid product
Maximize seal life by controlling the type of fluid film on the seal faces
Isolate the mechanical seal from atmospheric conditions
Provide an alternative when the process fluid will not provide stable and reliable lubrication of the seal faces (such as gaseous media, viscous fluids, non-settling slurries, or fluids liable to harden)
Establish a backup seal in the event of an inboard seal failure or planned equipment repair (or to identify seal failure during operation)
Avoid contamination of the process media should one seal fail
Mechanical Seal Questions
Q: What is a mechanical seal?
A: An end-face mechanical seal is a device used on a rotating shaft to seal fluids. It consists of two flat faces that are installed perpendicular to the shaft. One of the faces is mounted stationary to the seal chamber or housing. The other face rotates with the shaft to provide the primary seal. Axial mechanical force and fluid pressure maintain the contact between the wearable seal face materials.
A: A cartridge-mounted, end-face mechanical seal (cartridge seal) is a completely self-contained unit that consists of the sealing components, a gland, sleeve, and hardware that allows the unit to be pre-assembled and preset. This feature eases installation and maintenance on rotating equipment on which axial adjustments are required.
Q: What is a component seal?
A: Component, end-face mechanical seals (a component seal) consist of a separate rotating member and stationary seat that mount in a gland or housing. Since they are not preset, installation and maintenance are generally more difficult requiring experienced technicians to properly install and adjust them.
Q: What is an air seal?
A: Air seals are non-contacting, pneumatic devices engineered for sealing rotating shafts. They protect against product loss, emissions, and contamination by using small amounts of air or inert gas that is throttled to create positive pressure and an effective seal.
Metal Bellows
A metal bellows is a precision-engineered, flexible metal component that acts as a leak-tight seal– effectively separating two environments from one another. These versatile parts can convert changes in pressure, temperature, and position into linear motion and be used for rotary transmission that maintains flexible mechanical and electrical connections.
Metal bellows products are used in a wide variety of industrial and mechanical applications and are designed to compress, extend, or bend to absorb axial and angular movement. Some examples of useful applications for metal bellows include actuators, beamlines, expansion joints, mechanical seals, pumps, valve seals, thermal expansion tanks, reservoirs, and more. Metal bellows are available from MW Components in three varieties, which are differentiated by their fabrication method; these include edge-welded bellows, electrodeposited bellows, and hydroformed bellows. MW Components produces precision custom metal bellows using all three of these fabrication methods.
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