The term “labyrinth” conjures up images of elaborate mazes, and in the context of seals that really isn’t far from the truth. They are a fascinating use of fluid dynamics to prevent contaminant intrusion in an extremely effective manner. And these seals are used in everything from basic machine spindles to cryogenic turbopumps for rockets. There are many benefits of labyrinth seals.
A labyrinth seal is a specific type of dynamic mechanical clearance seal that utilizes a maze-like cross section to create areas of turbulence to prevent contaminants from making their way in and fluids from making their way out. They also reduce the clearance that is available for particles to enter. Labyrinth seals are most typically used to isolate an area of high pressure from an area of low pressure, but they work well in other applications as well.
In this week’s blog post, we will discuss the many benefits of labyrinth seals, their applications, and more!
How Labyrinth Seals Work
Labyrinth seals consist of two pieces referred to as the rotor and the stator. The stator attaches to the machine in which the shaft resides and remains stationary; the rotor, on the other hand, attaches to the shaft and rotates with it. The rotor and stator then interlock once installed to provide the seal. In fact, this design makes it relatively easy to install.
Any type of contaminant (e.g., particle, moisture) that tries to make its way past the seal must go through a maze-like combination of angles and turns that have been designed to generate enough turbulence to make ingression almost impossible. To cross the seal barrier, media and contamination must overcome significant flow friction and turbulence.
Even though labyrinth seals are a type of mechanical seal, they are non-contact because the two opposing seal faces (the rotor and the stator) do not come into contact with each other but rather a seperated by an extremely small gap. This effectively eliminates wear issues associated with traditional seals, which also means that labyrinth seals have a longer useful life and require less maintenance. In addition, the non-contact feature of these seals also means they are resistant to galling as well as generated contamination from seal erosion and wear.
And because they are non-contact they are also frictionless, which means there are no special concerns with lubrication. The fact they are frictionless also leads to elimination of stick-slip and starting torque. Perhaps even more importantly is the fact that they will enhance the efficiency of the systems in which they are used by reducing frictional losses. In addition, thermal effects will be minimal because of the elimination of heat generation from friction.
Highly Effective Sealing
Labyrinth seals can prevent media from leaking out while preventing ingression, which can be a serious challenge even for traditional seals with excluders. And labyrinth seals not only exclude particle contamination but moisture ingression as well, and can do so even when exposed to water sprays. These characteristics, combined with the non-contact nature of these seals, makes them extremely reliable compared to more traditional lip seal solutions.
Polymer Labyrinth Seals
When polymers, as opposed to elastomers, are used, there are additional benefits. For example, the right choice of polymer means a seal that is highly resistant to corrosion and chemical attack. Polymer labyrinth seals can be manufactured from a variety of materials, including PEEK (polyetheretherketone), Torlon PAI (polyamide-imide), Vespel PI (polyimide), and Fluorosint (enhanced PTFE).
PEEK offers excellent performance and is extremely resistant to chemical attack. PEEK labyrinth seals are available as a special type referred to as fix tooth labyrinth seals or rub tolerant seals. They make it possible to achieve an even more reduced clearance. When there is contact made between the seal and the shaft (i.e., rubbing), the fixed teeth are able to deflect to prevent both wear and damage to the rotor.
Torlon labyrinth seals offer superior mechanical properties under extended high temperatures and can be either compression or injection molded. They can be also configured as fixed-tooth seals and work the same way as the PEEK seals just described. In addition, Torlon meets several key requirements such as FAA requirements for smoke density, toxic gas emissions, and flammability, as well as UL approval with regard to vertical flammability.
Abradable labyrinth seals are designed with the seal and rotor are reversed such that the seal wears away and not the teeth if they come into contact. This makes it possible to design the seals with only enough clearance for installation. Abradable labyrinth seals work extremely well when either the stationary and rotating elements are extremely close to each other or in cases where the rotating element grows axially or radially toward the stationary element. The most popular material for abradable labyrinth seals is modified PTFE. In particular, low LCTE (coefficient of thermal expansion) modified PTFE (often called Fluorosint) is used as a base for the seal, providing a wide operating temperature range, outstanding chemical resistance, and extremely low friction.
Labyrinth seals are an excellent option for separating areas of low pressure from those of high pressure, as well as applications that demand a sealing solution with extremely small clearances. The benefits of labyrinth seals include excellent reliability, long operating life, low friction, improved efficiency, and easy installation when compared to their traditional counterparts. When engineer polymers are used, sealing solutions are possible that can withstand corrosive media and offer superior mechanical properties even in the presence of continuous high temperatures.
If you are looking for a sealing solution where traditional options have failed, contact Advanced EMC today to find out how a polymer labyrinth seal can benefit your application.