Mechanical Seals

What are mechanical seals ?

Power machines that have a rotating shaft, such as pumps and compressors, are generally known as “rotating machines.” Mechanical seals are a type of packing installed on the power transmitting shaft of a rotating machine. They are used in various applications ranging from automobiles, ships, rockets and industrial plant equipment, to residential devices.
Mechanical seals are intended to prevent the fluid (water or oil) used by a machine from leaking to the external environment (the atmosphere or a body of water). This role of mechanical seals contributes to the prevention of environmental contamination, energy saving through improved machine operating efficiency, and machine safety.

Shown below is a sectional view of a rotating machine that requires the installation of a mechanical seal. This machine has a large vessel and a rotating shaft at the center of the vessel (e.g., a mixer). The illustration shows the consequences of cases with and without a mechanical seal.

Cases with and without a mechanical seal

Without a seal

• The liquid leaks.

With gland packing (stuffing)

• The axis wears.
• It needs some leaks
  (lubrication) to prevent wear.

With a mechanical seal

• The axis does not wear.
• There are hardly any leaks.

This control on liquid leakage is called “sealing” in the mechanical seal industry.

Without a seal

If no mechanical seal or gland packing is used, the liquid leaks through the clearance between the shaft and the machine body.

With a gland packing

If the aim is solely to prevent leakage from the machine, it is effective to use a seal material known as gland packing on the shaft. However, a gland packing tightly wound around the shaft hinders the motion of the shaft, resulting in shaft wear and therefore requiring a lubricant during use.

With a mechanical seal

Separate rings are installed on the shaft and on the machine housing to allow minimal leakage of the liquid used by the machine without affecting the rotating force of the shaft.
To ensure this, each part is fabricated according to a precise design. Mechanical seals prevent leakage even with hazardous substances that are difficult to mechanically handle or under harsh conditions of high pressure and high rotating speed.

How are mechanical seals used?

The following are example uses of a mechanical seal in a pump.

Mechanical seal in pump structure

1.Internal structure of pump

A pump is a machine that works to move fluids, as in lifting a liquid to its inside. For example, its impeller rotates to move water.

2.Mechanical seal installation location in pump

A mechanical seal is installed on the impeller rotating shaft. This prevents the liquid from leaking through the clearance between the pump body and the shaft.

3.Mechanical seal installation location on shaft

Mechanical seals are mostly comprised of two rings: a rotary ring on the shaft and a stationary ring on the pump housing.

4.Mechanical seal structure (stationary and rotary rings)

The rotary ring rotates with the shaft. The stationary and rotary rings rub against each other ensuring a clearance in the order of micrometers maintained between them. Where they rub against each other, they are referred to as “face materials.”

The essential point is to control leakage and friction.

The face materials where the stationary ring and the rotary ring rub against each other are the most important portions as a barrier to the fluid. If the clearance is too small, the friction increases, hindering the shaft motion or resulting in seal breakage. Conversely, if the clearance is too large, the liquid will leak. Consequently, it is necessary to control the clearance in the order of micrometers to prevent leakage, but at the same time ensuring lubrication by the fluid, thereby reducing the sliding torque and avoiding hindrance to the machines’ rotation.

Technologies behind mechanical seals

The mechanical seal technology is a sum of mechanical engineering and physical property technology due to the above-mentioned functions and applications. More specifically, the core of the mechanical seal technology is the tribology (friction, wear and lubrication) technology used to control the surfaces where the stationary and rotary rings rub (slide) against each other.

Mechanical seals with improved functionality will not only prevent the liquid or gas handled by a machine from leaking to the outside, but also improve machine operating efficiency, thereby helping achieve energy saving and prevent environmental contamination. Moreover, in some cases, rotating machines handle media that, in the case of leakage, can lead to a dangerous accident. Therefore, mechanical seals are required to be highly reliable through manufacturing backed by solid engineering expertise.

These functions and roles will make mechanical seals increasingly important functional parts in the future. Their further technical innovation is anticipated. To positively respond to these expectations, Eagle Industry is working on technical research and development every day.

Trend of applicable range of mechanical seals

The mechanical seal technology was fundamentally established in the 1960s. Thereafter, it has been making significant progress by introducing various leading-edge technologies, and innovative mechanical seals created from the above advanced technology are continuously being put to practical use.
To meet the demands of the market sufficiently, an applicable range of the “pressure” and “rotation speed” of mechanical seals has been considerably extended since the beginning of the 2000s. This is due to advancing of the tribology technology such as to enhance a function of the sliding materials (e.g., composite material composition, coating technology) and/or a performance of the sliding surfaces based on the fluid lubrication theory (e.g., non-contact mechanical seal, surface textured mechanical seal). These advanced technologies are sustained by improvement in the element technology of numerical analysis, processing/production, physical property/composition analysis, measurement, verification test, and so on.

Source: “Current status and future prospects of a wind/hydraulic machinery industry from 2021 to 2025”, The Japan Society of Industrial Machinery Manufacturers (2021).

Major Differences Between A Lip Seal And CinchSeal

It can be hard to understand what people are talking about when it comes to shaft seals. Not only are there quite of few kinds—O-rings, braided packing, mechanical face seals and so on—but it’s sometimes difficult to know which kind is under discussion. For example, lip seals have been called mechanical seals, which causes them to get confused with mechanical face seals. If you’re not an expert, it can get messy. But don’t worry, in this blog post, we will discuss two kinds of shaft seals — the lip seal and CinchSeal.

What’s the Difference Between a Rotary Shaft Lip Seal and CinchSeal?

Lip seals and CinchSeal have at least one thing in common. They serve the same purpose: preventing leakage and excluding contamination of the product being mixed or conveyed. However, there are major differences in the way these seals do their job and how well they do it.

Lip seals and Mechanical Packing

Rotary lip seals maintain a thin layer of lubricant between the “lip” and the shaft. The hydrodynamic action created by the turning shaft causes a pump action that helps hold the seal. The lip makes point contact with the shaft that forms two angles, and it is this contact with the rotating shaft that wears and damages the shaft. That is the major difference between a lip seal and CinchSeal.  

Lip Seal Advantages:

• The biggest advantage of lip seals and mechanical packing used in stuffing boxes is their low cost, making replacements relatively inexpensive (but keep in mind that replacing these and product loss will take away from the initial savings).

Lip Seal Disadvantages:

• Lip seals have a comparatively small surface they can grab the rotating shaft with. This design increases the risk of contamination and leakage in all applications of lip seals. Eventually, contamination creates a groove in a shaft and destroys bearings and gearboxes due to particle contamination.
• The small surface area of the lip also makes lip seals wear out more quickly, especially in harsh operating environments. This requires lip seals to be replaced more frequently, eliminating much of their initial cost-saving benefit.
• Lip seals have limited applications as their stationary design causes friction and heat generation. The viscosity of the sealed fluid will directly influence the friction generated in the lubrication film. For low viscosity fluids this can be a serious problem as the lubricant film becomes too thin to maintain the separation of the seal and the shaft.
• Lip seals don’t withstand high pressure well, limiting their usefulness.
• The non-rotating lip seal design can also cause shaft damage in a short period of time.
• Finally, lip seals lack government certification necessary in meat, poultry and dairy processing industries. 
• Mechanical packing is square braided rope packing that is compressed around the diameter of the shaft in a stuffing box. Packing wears with normal equipment operation and needs to be replaced often, which can be costly.
• When abrasive bulk material is conveyed, it migrates into the seal area and becomes impregnated into the rope packing. The abrasive material starts to wear down the outside diameter of the shaft. The smaller shaft diameter reduces the strength and torque rating of the shaft and makes the sealing surface uneven and difficult to seal.

CinchSeal’s Rotary Shaft Seals

CinchSeal, on the other hand, represents a relatively new innovation designed mainly for mixers, screw conveyors, ribbon blenders, and all kinds of bulk-handling equipment. The rotary shaft seals provide a high ROI, protect bearings and gearboxes, eliminate shaft wear and product leakage. Compared to lip seals and packing, CinchSeals eliminate unscheduled maintenance and downtime.

The self-adjusting design is made possible because the elastomer sealing element provides constant pressure against the sealing surfaces. Most shaft seals require periodic adjustment to prevent leakage. The CinchSeal is repairable and designed to disassemble so the sealing element can be replaced. Its replacement is much more cost effective than replacing the complete seal unit. Since the CinchSeal is self-adjusting, little or “near zero” maintenance is required.

CinchSeal Advantages:

 The CinchSeal has advantages over lip seals and mechanical packing in virtually every rotary seal application:

• The CinchSeal unique rotating design eliminates the risk of shaft damage, inherent with lip seals and mechanical packing.
• CinchSeal can tolerate shaft misalignment of up to ¼ inch, common in bulk-handling equipment, without losing its seal. This prevents leaks and material loss.
• CinchSeal has a larger surface area than a lip seal, reducing the chance of contamination and leakage.
• The seal’s self-lubricating design enables a dry-running seal operation, decreasing its wear and tear.
• CinchSeal is USDA certified for meat and poultry, and dairy applications. In such hygiene-sensitive environments, it is vital to quickly disassemble and clean equipment on a daily basis.

Summary

Lower price does not translate to ROI value when it comes to deciding between rotary shaft lip seals and Cinchseal. Frequent repair and replacement of lip seals quickly eat into initial savings. It’s important to consider all costs related to your shaft seal choice when selecting the best solution for your application.

For over 25 years, CinchSeal has been a global leader in manufacturing innovative rotary shaft seals that serve as replacements for existing lip seals and mechanical packing, making machine replacements much less likely. We offer a variety of rotary shaft seals by size and design, so that you can find the right ones for you. If you would like a quote for our industrial seal solutions, contact us now. Quotes and drawings are guaranteed to be available in 24 hours, and custom engineering usually takes 10 days.