unhappy airline customer

APU Mechanical Seals Case Study

A sealing problem causing noxious cabin odor made airline passengers very unhappy. The manufacturer needed a reliable solution. Technetics provided it the first time, thanks to our rigorous and thorough design process.



unhappy airline customer

APU Mechanical Seals Case Study

APU Mechanical Seals Case Study

A Small Issue with Far-Reaching Reputation Implications 

Imagine — You’re leaving for a work trip for a big meeting. The Uber arrives on time, and you have plenty of time to get through security and even grab a coffee. Boarding the plane goes flawlessly, and the flight attendant warmly greets you, letting you know everything is on time. You internally rejoice over the small wins. 

But as soon as you board the plane, you notice a foul smell. You think, ‘it must be from the plane resting; it’ll get better once we take off.’ However, it doesn’t get better. The odor persists the entire flight, and it’s so bad that multiple people have complained. The plane lands, everyone claps and immediately gets on social media to spread the word about the issue. 

You decide to change your return flight to another airline. Now, every time you think of the airline, you think of the rancid smell you endured for five hours on your way to the biggest deal of the year, and you consciously avoid that airline in the coming years.  

This may be an extreme example, but smell and memory are highly connected, so it’s not a far-off scenario. And while the story is fake, the problem was very real for a modern-day airline. The plane had a major sealing problem: the carbon-face seal in the auxiliary power unit was routinely leaking, causing cabin odor. 

Technetics — Turning Problems into Solutions 

 The airline first chose to confront the issue with a Technetics’ competitor to save costs. However, the competitor’s seal didn’t resolve the problem. So, why would this airline trust yet another seal solution provider? It’s simple: Our reliability and quality are unmatched.  

Let us describe our rigorous and thorough solutions process —partnership, design, analysis, and testing — to explain how our solutions deliver the first time, every time.  





Building trust. 

By working directly and intimately with our customers, we focus on forming and maintaining trust throughout the entire process. We remain open, honest, and communicative while finding the perfect solution to meet your needs. 

 Designing the solution. 

We gather any additional information needed to deliver a preliminary design, compliance matrix, and schedule through the design specs you provide. We use the compliance matrix to identify all the requirements and how each will be validated while the plan mitigates any high-risk design requirements. We keep the lines of communication open throughout the design process. Our strict adherence to the schedule ensures we allocate the necessary resources appropriately.  

 

Analyzing the solution. 

Our rigorous analysis process ensures the ideal outcome every time for our customers. 

We first work to analyze the surrounding components, like operating environments, materials, configuration, and assembly. Using our FEA tool to review seal components, we can predict distortion effects, vibration, and seal face loads.  

 Through the analysis, we may suggest using a metal bellows as a secondary seal, which helps provide a spring force to keep the sealing faces closed during shutdown. This design helps improve stress analysis. We may perform additional testing where necessary to ensure we meet design requirements.  


 Next, we’ll determine if a contacting or non-contacting seal design is appropriate. For non-contacting seals, we use hydrodynamic face seal designs for high-speed applications that need low-pressure differential, like sealing small main-shaft locations. We’ll include lift-off speed and high-altitude condition predictions during this analysis stage. Other variables, such as film thickness and stiffness, are also considered.  

Maintaining flatness is a crucial element of good hydrodynamic performance. We also investigate rotor deflection by ensuring the face seal designs maintain flatness and lubrication while managing deflections. 

Finally, our engineers will analyze the leakage and seal life. While lubrication film is required to maintain face temperature by cooling the interface, it also allows unwanted leakage. This step was essential for this airline’s case since leakage could cause the solution to fail. However, our design toolkit can predict the leakage rate and heat generation, which also helps estimate the seal life. 

Testing the solution. 

After the prototyping phase and we begin building parts, the production and validation phases start. This includes considering the face load versus the drum loading and a vacuum check to determine the quality of the secondary seal.  

Additionally, we make use of four dynamic test rigs to simulate the quality of the solution for your exact scenario, like outburning pressures, speeds, and temperature conditions. Then we conduct another round of leak rate, wear, and face pressure testing.  






Lift Off Seal


Technetics — Your Trusted Engineered Solution Provider. 

For this airline customer, we used the bellows energized hydrodynamic lift-off seal. The seal has performed flawlessly, and the customer’s air cabin odor issue has now been resolved. Because we leveraged the tools and processes described above, we could find a solution the first time. 

With our robust and thorough quality system, we continue to invest in the industry’s demanding requirements and ensure that every expectation is met. Our solution process described above — paired with our fully integrated business software specifically designed for manufacturing and hiring top talent — are just a few reasons we lead the industry in quality and satisfaction.  

At Technetics, we welcome a challenge and love meeting customers’ needs. Ready to tackle your solution together? Contact us today. 

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Non-Contacting Lift-Off Seal


Non-Contacting Lift-Off Seal

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Qualiseal wins over customers with custom design, verification, and field testing. In-house lab testing shortens the validation process by a factor of years. A rigorous design and review process provides customers with peace of mind. The team maintains the relationship with superior customer service.

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Design features in the face of the mating ring force fluid (air, gas) into a converging gap in the sealing face. As the pressure builds, the faces separate.

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Qualiseal® Radial Shaft Seal


Qualiseal® Radial Shaft Seal


In certain extreme applications, a part made of individual segments may meet your critical performance requirements better than a single-piece unit.


QUALISEAL® CONTROLLED GAP/BUSHING

Really two pieces in one, Qualiseal® Controlled Gap/Bushing seals are the best solution when pressure is an issue.

Controlled gap or bushing seals are comprised of a carbon insert that is shrink-fitted into a separate retaining band. This floating circumferential ring assembly grows at a rate similar to that of the shaft when exposed to elevated temperatures.

Under normal operating conditions, the pressure on the airside is higher than the pressure on the oil side. This creates some air leakage through the controlled gap between the carbon ring and shaft. The differential air pressure, along with the spring load, provide the closing force necessary to maintain contact between the carbon and housing secondary sealing face. Meanwhile, the shaft turns freely within the carbon ring.

The seal design also features a unique stabilizer ring with fins which minimize stress on the carbon ring, thereby maintaining the roundness of the circumferential ring assembly. The dimensional tolerance of the critical inside diameter of the bushing ring is tightly controlled to minimize leakage variations.



Product Applications


  • Aerospace Industry
  • Industrial Industry
Ideal For:
  • High-pressure applications
  • Also suitable for sealing low-pressure liquids

Features & Benefits


Benefits:
  • Minimal leakage in an exceptionally wide temperature range
  • Tolerance to unlimited shaft axial movement
  • Very long life
  • Very low heat generation
Features:
  • Rides on a buffer that centers the ring and minimizes seal-to-shaft contact
  • Available in a wide variety of materials suitable to a broad range of applications
  • Often paired with other seals to create sealing systems that meet demanding requirements
Design Configurations:
  • Single seal for dual pressure conditions
  • Spring-loaded double back-to-back seal
  • Separable designs to facilitate replacement and/or rework of internal components
  • Double tandem seal arrangement for sealing a combination of liquids and gases
  • Multiple labyrinth ring assemblies
  • Housing for mounting directly onto equipment case

QUALISEAL® SEGMENTED SEALS

Segmented seals ride directly along the shaft and are primarily used in low-pressure applications.

These seals contain a series of segmented carbon rings which contact the shaft or rotor. Segments inside the seal housing are kept in the proper location by anti-rotation keys or pins. A secondary seal is formed by the axial spring loading of the seal rings against the internal surface of the housing face. During movement, a continuous seal is always in contact with either the primary or secondary sealing surfaces.



Product Applications


  • Aerospace Industry
  • Industrial Industry
Ideal For:
  • Gas seals and for sealing low-pressure liquids

Features & Benefits


Benefits:
  • Tolerance to unlimited shaft axial movement
  • Prevents oil and contaminant migration into the process gas side
  • Leakage rates remain constant over the life of the seal
Features:
  • Rides directly along the shaft
  • Special gap segments permit the seal to adjust dimensionally for minimal leakage
  • Compression and garter springs ensure that segments remain in contact with mating surfaces during low delta pressure and shutdown conditions
Design Configurations:
  • Various seal ring segment configurations
  • Pressure-balanced segments
  • Fractured rings
  • Multiple seal labyrinth
  • Internally pressurized seal
  • Internally vented seal


SPEAK WITH A SPECIALIST

Have questions? A Technetics Group product specialist will get back to you to shortly.


Specifications



Resources

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