What are Bushing Seals? Everything You Need To Know

bushing seal

Bushing seals have always been an integral part of applications susceptible to fluid or gas leaks. So, often, you’ll find one on your rotating shafts and high-pressure oil-filled or gas-filled cables.

Are you wondering what it is there for? Or why should you care? Read on as we cover the ABCs of bushing seals, including the types and some intriguing key features.

Let’s dive in.

What Are Bushing Seals?

Put simply, a bushing seal is a sleeve-like and cylindrical mechanical seal that helps you prevent gas or oil flow out of the system. Here’s what that looks like.

Here's what that looks like

For instance, the oil or gas-filled pipe-type cables are usually placed in a conduit under high pressure for electric rail track applications. If this system perhaps suffers oil leaks, it may cause molecular damage to the cable’s insulation system, which can cause the cable to fail. 

When the cable fails, it takes a toll on the overall railing system. A conduit seal bushing is used to engulfs this conduit, forming a small clearance and limiting the probability of leakages.

Bushing-type seals also make excellent shaft seals to rotating shafts with fluid-filled passages, these fluids are there to minimize friction and heat on the shaft. The bushing seal serves as the leak-proof component of these shafts, preventing the fluids embedded in them from leaking out. 

Generally, bushing seals are non-contacting. In essence, there is no direct contact between them and the surface they are sealing. Depending on their application, they feature variable clearance gaps that minimize the tendency for wear and friction. 

Types Of Bushing Seals

There are several types of bushing seal designs, but five of the most common types include:

Fixed bushing seals

The fixed bushing seal maintains a constant close clearance with the surface it is surrounding. Here’s what it looks like. 

surface it is surrounding

You’d typically find this type of bushing in applications that do not involve mechanical gyrations. An example is the cable conduits and transformers.

However, in cases where gyrations are involved, you need a bushing seal that can float the sealed components. An instance is in a spinning shaft, which works by rotating. If the seals don’t float with the spin, unwanted contact will occur, leading to wear and tears. 

Floating bushing seals

Floating seals, unlike the fixed bushing seals, follow the mechanical rotations with tolerances that are relatively closer than the fixed types. Here’s what the floating bushing seal looks like in practice. 

bushing seal looks like in practice

In addition, floating bushing seals move radially with spring loading tailored to accommodate the movements of the sealed material.

Floating ring bushing seals

Normal floating bushing seals may be subject to pressure and alignment problems, but floating ring bushing seals help overcome these problems by splitting the bushing into multiple rings. Here’s an example. 

splitting the bushing into multiple rings

From the illustration, you’ll notice the shaft is enclosed by an outer and inner ring seal, which is how the floating ring busing seals work. 

Balanced bushing seals

The balanced bushing seals feature components that minimize the tendency for spring forces to occur. On top of that, it maintains the advantages and features of the floating bushing seals. Here’s an illustration of this type of seal. 

illustration of this type of seal

It’s essentially a form of floating bushing seal, but without the springs. 

Segment bushing seals

The segment bushing seals are highly tailored gas seals that you’ll most often find in aircraft engine shafts and rockets. Here’s an example. 

engine shafts and rockets

The segment bushing is a circumferential seal made from carbon-graphite and antimony impregnation. The segment bushing seal is suitable for both axial and radial sealing operations.

Key Features of Bushing Seals

Bushing seals are generally non-contacting seals. As such, your system is less susceptible to wear, tear, and other adverse effects of contact, which improves its lifespan leading to lower maintenance costs.

But remember that if the entire conduit is passing through a duct, other external vices like a rodent, water, etc., may result in long-term bushing seal damage. So, you might need a duct sealing system to completely maximize its lifespan.

Another key feature of Bush seals is they can withstand high-temperature ranges of up to 300 degrees Celsius. Plus, they perform superiorly to prevent leakages at up to 20,000 kPa of gas and fluid pressure. Bushing seals are also flexible. You can design them to meet the highly tailored specifications of your system.

Suppose you have applications that are above the temperature and pressure parameters mentioned before. In that case, the flexibility of bushing seals allows you to combine them with other types of seals, like wiper seals, to suit your requirement.

Generally, bushing seals feature considerable tolerance for axial movements. On top of that, they are less likely to generate heat in applications that involve mechanical gyrations. Further, due to their fire retardancy property, they do not support combustion. Thus, making the sealed part of the system somewhat fire-proof.

Finally, this type of seal is also easy to install. You don’t have to compound the thread of the conduit or make other preparations at the end before they are ready to use, like with other high pressure seals. 

Overall, these terrific features are what make sealing bushings perfect for applications with higher static pressure than what traditional sealing systems can handle.

In Closing

Whether you’re working with a shaft or capable conduits, a bushing seal is a component you can’t overlook. 

This type of seal helps you bring the tendency of oil and gas leaks to the barest minimum. While there are wide varieties of bushing seals available, this article ranged through five of the most common types; floating, balanced, fixed, floating ring, and segment bushing seals. 

Now that you understand what these types entail and the key features, you have all it takes to make a better-informed decision on your next sealing system.


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