In the process industry, dependability of pivoting hardware&#;s is of most extreme significance, which depends on the capacity largely to keep away from spillage through shafts. These mechanical seals help in avoiding leakages. It is critical that clients/administrators appropriately keep up the mechanical seals. In this way, it is essential that an intensive utilitarian comprehension, establishment prerequisite and disappointments of mechanical seals.
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ESSENTIAL FUNCTIONS OF MECHANICAL SEALS
The important function of a mechanical seal is to seal the opening where the pole enters the pump, avoiding liquid leakage. Originally mechanical seals were created to conquer the negative issues partnered with pressed stuffing boxes. Straightforward mechanical seals offered the other option to liquid spillage; none, minimum not distinguishable with the clear eye. Mechanical seals can deal with significantly higher temperatures and weights than at any other time and can meet zero resilience wrongful discharge benchmarks.
MAIN ADVANTAGES/DISADVANTAGES OF MECHANICAL SEALS
A portion of the favourable position and disservice of mechanical seals over customary packings and lip seals are recorded underneath.
MAIN ADVANTAGE
- It handles a wide range of liquids including acids, salts and rough particles.
- Long working life.
- Mechanical seal handle marginally misaligned/non-concentric
- The operation of does not bring about shaft wear.
- Shaft condition is not basic
- Handle Bi-directional shaft revolution, huge weight, temperature and speed trips.
- A positive fixing for sustenance preparing, dangerous chemicals and radioactive liquids.
DISADVANTAGE
- It requires more space than outspread lip seals.
- Mechanical Seals cannot normally deal with pivotal end play.
- Sealing countenances must be done smooth (0.08 to 0.4 micrometer) and can get effectively harmed.
- High beginning expense.
Single mechanical seal
Advantage
Almost 90% single mechanical seal are installed on regular basis. For the most part in single mechanical seals, the pumped liquid ought to be cool, not unpredictable, have great lubricity, not contain rough or broke down solids. The single seal is the most conservative fixing gadget among mechanical seals as it has the least number of parts. Assist by, and large pumping liquid is utilised for seal grease. If the pumped liquid is not tasteful as a fixing liquid, a helper liquid can be infused over the seal confront.
Limitations
The impediments with single mechanical seals are that if seal spills there is no move down accessible. Likewise, framework disturb causes the glimmering of fluid and blazing causes harm of appearances.
Double Mechanical Seal
Disadvantage
A few liquids are not perfect with a double mechanical seal pumps. Regularly these fluids convey rough material in suspension that would quickly wear the seal faces, or the fluid might be destructive and dangerous. There are two answers for this issue. One is the use of natural controls, and the other is the utilisation of multiple seals or double mechanical seals.
Conclusion
One of the inconveniences of a double mechanical seal pump is its low weight constraint. If the end compels applied on the seal confront surpasses that farthest point, the greasing up film between the countenances is crushed out and soon the appearances get pulverised. This issue is overcome by balancing seals.
For hundreds of years, packing has been used to minimize leakage from pumps and rotating equipment. As rotating equipment has evolved, however, so has the need to minimize that leakage even further.
Without some sort of sealing mechanism, process fluid easily leaks out of pumps through the gap surrounding the shaft as it enters the pump housing. For years, pump packing has been used to reduce leakage and minimize the space or clearance between the shaft and pump housing.
The very first patents for mechanical seals appeared in the early s. Since that time, a wide range of seal technology has emerged, ensuring there&#;s a seal for nearly any application.
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There are perks to both mechanical seals and pump packing, so which is right for the application at hand? In this post, we&#;ll discuss the pros and cons of each.
Pump Packing
Pump packing comes in many different types and materials. The most common is probably braided compression packing. This type of packing can be made of carbon, graphite, or synthetic materials.
Compression packing is cut to length, formed in rings, and installed in the pump&#;s stuffing box. The rings are mechanically compressed to reduce leakage.
When the pump is running, liquid enters the stuffing box under hydraulic pressure. The liquid flows under the packing rings and eventually makes its way out of the packing gland. If the packing leaks too much, it can be tightened by the operator or mechanic. Note that the packing&#;s job is to reduce leakage. Not prevent it entirely.
Pump packing is an inexpensive method of sealing pumps and installs easily. Operators and maintenance teams must determine, however, if these benefits outweigh the disadvantages of packing.
Packing is expected to leak. It is common practice to try to control the leaking to 10-15 drops per minute. To maintain this rate, the packing must be monitored and adjusted daily. The leakage cools and lubricates the packing. Without leakage, the packing will burn and wear grooves into the shaft and sleeves.
Over time, packing wears and loses material causing it to leak more than desired. A mechanic or operator must tighten the packing gland again. Adjustments are made frequently and have no set degree of tightening.
Because of this, mistakes are easily made and packing glands are often over-tightened. Over-tightened packing glands oftentimes shorten packing life as the packing overheats and rapidly deteriorates.
Improper packing of the stuffing box can cause rotating equipment to consume more power than mechanically sealed equipment as it works to overcome the friction imparted by packing. Learn more about packing installation in our post "Terms You Need To Know For Packing Installation in Centrifugal Pumps".
Packed pumps and rotating equipment require more maintenance resources as well. This equipment is down more often than mechanically-sealed equipment due to corrosion problems, bearing failures, and shaft sleeve replacements.
Though the packing itself is less expensive than mechanical seals initially, there are other costs associated with this sealing method. Those costs include housekeeping, product loss, and additional power consumption.
Mechanical Seals
Alternatively, mechanical sealing methods can provide many benefits over pump packing. There are many options for mechanical sealing. Single seals are the most common.
Mechanical seals consist of two flat surfaces (materials could include tungsten carbide, silicon carbide, or carbon graphite) compressed by a spring against each other. Just like packing, mechanical seals also require a small amount of leakage. However, the leakage is small, or not noticeable at all.
The pumped product generates a light film of fluid between the seal faces. The film prevents the faces from touching, lubricating them, and absorbing the heat generated from the associated friction. The fluid crosses the seal face as a liquid, then vaporizes into the atmosphere. Single mechanical seals are common practice when the pumped product poses little to no risk to the environment.
Like pump packing, the mechanical seal does leak. But unlike pump packing, in many applications the leakage is so small it&#;s practically invisible. This means there&#;s no mess on the floor to cause potential safety hazards. With less leakage, there&#;s less product loss.
Mechanical seals do not impart friction on the rotating equipment shaft. Therefore, it&#;s more energy-efficient than packing.
One disadvantage to mechanical seals is the complexity involved with the installation. Proper installation is critical to the long-term success of the seal so it&#;s important that they&#;re installed by trained professionals. Check out this blog post we wrote about mechanical seal installation, &#;5 Ways to Kill A Mechanical Seal During Installation&#;.
Here&#;s a video to demonstrate proper installation.
Although mechanical seals require a higher initial dollar investment, when properly applied, they can run for over 10 years without failure or adjustment. When considering the cost of replacing and maintaining packing, installing a mechanical seal will cost less than pump packing over the lifetime of the equipment.
Which Sealing Option is Best?
The biggest advantage to mechanical seals over pump packing is the minimal amount of maintenance. Packing requires frequent adjustment and replacement, not to mention the upkeep that comes with constant leaking.
On the flip side, the upfront cost is substantially higher for a mechanical seal over braided packing or other types of packing. Teams must decide for themselves if the maintenance required to properly care for packed rotating equipment is sustainable.
If it&#;s decided to look into replacing packing with mechanical seals, get an engineer involved to help select the right seal for the application. Seals can be expensive and with hundreds of options to choose from, it&#;s best to lean on the expertise of someone who frequently selects them.
Need help selecting the right mechanical seal for your process? Ask us about it! We gladly provide technical expertise to manufacturers and municipalities in Wisconsin, Minnesota, and upper Michigan.
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