Types of Sealing for Mechanical Applications

All machines that flow or handle fluids require some leak-prevention mechanism. When fluids or gases leak, the efficiency of the equipment is decreased, safety is compromised and energy expenditures increase. This is where seals come in. A mechanical seal is a device that prevents liquid or gas leakage as a rotating shaft moves. It is small in size but plays a huge role in performance.

Pumps, compressors, and mixers would not be able to work safely and reliably without the right seal.

In this article, we will consider the key types of seals for mechanical applications, their importance, and discuss how you can select the right type for your application.

What is a Mechanical seal?

A mechanical seal is a seal that is fitted between a rotating shaft and the housing to prevent leakage. It retains process fluids in their proper places while allowing rotation. Consider pumps, mixers, or compressors, where liquids or gases are required to be retained as something rotates (say an impeller) - this is where mechanical seals come in. 

They are composed of two principal surfaces: a fixed one and a rotating one. These two faces press together with a delicate balance, and their smooth, tight fit forms a barrier to leakage.

Why are they important? 

Seals are very important in protecting the environment and the machine. Leakages of fluids may cause damage to equipment, result in downtime and unsafe situations. Seals are essential in some industries such as oil and gas, chemical processing, water treatment, and power generation. They assist companies to save on maintenance expenses, enhance productivity and comply with environmental regulations.

6 Types of Mechanical Seals

Let's talk about some of the most commonly used seals in industry today:

Gas Seals

Gas seals are widely used in high-speed machines like centrifugal compressors. They use gas instead of liquid to create a thin film between the faces. 

• Wet gas seals use oil or another liquid to form this film. While effective, they tend to leak more. Reports show that wet seals may leak between 40 and 200 cubic feet of methane per minute.
      

• Dry gas seals use process gas or nitrogen instead of oil. They leak much less, around 6 cubic feet per minute in a two-seal setup. They are also less energy intensive, and easier to maintain. Research indicates that by replacing wet seals with dry seals, there would be a reduction of up to 97% of methane emissions, and in many cases, such investments can pay off within one year.

O-ring Mechanical Seals

O-Ring mechanical seals include O-rings, flat gaskets, and metal rings. They are simple but very effective.

• O-rings are small rubber rings that fit into grooves and block leaks in static joints.

• Flat gaskets sit between two flat surfaces and compress to seal gaps.

• Metal rings are stronger and used where more durability is needed.

Ring seals are affordable and easy to install. However, they are better suited for static applications than for rotating equipment.

Gaskets

A gasket is another common seal type. It is a sheet or ring made from rubber, plastic, graphite, or metal. It is placed between two surfaces to stop leaks. Gaskets fill small surface imperfections and keep pressure tight.

Spiral-wound gaskets or kammprofile gaskets are advanced gaskets that are used in high-pressure environments. They are more costly, but they last longer and provide a secure seal. Gaskets are found in pipelines, engines, and flanges where flat surfaces meet.

Radial Shaft Seals

Radial shaft seals, or lip seals, are commonly used in pumps, gearboxes and vehicles. They have a flexible lip that touches the shaft and keeps oil inside while stopping dirt from entering. A spring often holds the lip against the shaft to keep it tight.

These seals are compact and cheap. They perform well at medium-pressure and medium-speed installations. But they are not the best option for high temperatures or very high pressures.

Cartridge Mechanical Seals

Cartridge seals are complete units that come pre-assembled from the factory. They include the gland, sleeve, and seal faces all in one. It is simple to install: the cartridge is fitted on the shaft and fastened with a bolt.

This design saves time and eliminates the risks of installation errors. They are more expensive initially but save money in the long term by eliminating errors, and last longer.

Pusher Seals

Pusher seals use springs to push the seal faces together. As the seal wears, the spring moves to keep the contact tight. This makes them cost effective and flexible. Unlike the primary seal, which is fixed, the secondary seal (an O-ring) moves and may wear out more easily. That makes them less convenient to dirty or abrasive fluids.

A related type is the non-pusher seal (like a bellows seal). These contain bellows instead of springs, and this prevents wear. Bellows seals are preferable with very hot, cold, or dirty fluids, but are more expensive.

How to choose the right type for your application

With so many types of sealings available, choosing the right one for your system becomes even more difficult. The selection of the correct seal is based on the working conditions of your machine. The following are some other key things to consider:

• Fluid type: Is it clean water, corrosive chemical, or gas? For gases, dry gas seals work best. For hot or dirty fluids, bellows seals are better.

• Pressure: High pressure needs balanced seals or gas seals. Lower pressure can use simpler seals.

• Temperature: Extreme heat or cold requires special designs like bellows seals.

• Leakage tolerance: If you need almost no leakage, go with dry gas seals or double seals.

• Maintenance: If you want easy installation and less downtime, cartridge seals are a smart choice.

• Cost: Simple O-rings or pusher seals are cheaper, while dry gas and cartridge seals cost more but save money over time.

Conclusion

Mechanical seals can be tiny, but they perform one of the most critical tasks. They retain fluids, safeguard equipment and decrease downtime. Ranging anywhere between the ordinary O-rings to advanced dry gas seals, all of them serve different purposes. The right choice depends on factors like pressure, temperature, fluid type, and budget. Choosing a wrong seal type can result in costly downtime and choosing one correctly means trouble-free and safe operation for years.

When you want to upgrade or replace the seals, it is important to consult with experts or partner with a reliable supplier. That's why Lepu Seal offers a variety of quality sealing solutions designed to fit various industrial requirements.