Video: The mechanical seal explained

How do you prevent liquids and contaminants from disrupting a process? The answer lies in a component that is often smaller than a coffee cup, yet plays a key role in everything from pumps and mixers to heat exchangers. And here we are talking about the mechanical seal. 

Although the mechanical seal is a small part of a large plant, its function is crucial to avoiding costly leaks and unplanned downtime in the food or pharmaceutical industries. By understanding its design and maintenance, you can optimise both the service life and cost-effectiveness of your production. 

In this explainer video, we zoom in on mechanical seals to clarify what they are and what components they consist of. 

Mechanical seals – also known as stuffing boxes – are used in rotating equipment such as pumps, agitators, compressors and mixers. The purpose is to create a tight barrier between the shaft and the equipment housing, ensuring that liquids and gases remain within the desired limits. This solution also protects the process environment from external particles and air. 

In hygienic applications, the sealing function is critical. Here, it is not only a matter of operational reliability, but also of protecting the end product from contamination and ensuring that cleaning and CIP processes function effectively. 

The seal itself consists of two main components that work together to create the seal: 

• A rotating part that follows the movements of the axle
• A stationary part, which is fixed in the pump house. 
• Precision-ground sliding surfaces, which are pressed against each other by a spring to ensure constant contact.  

Choosing the right seal requires an understanding of both your machine and your process. Here are the key factors you need to consider: 

The choice of material for the sliding surfaces is crucial for durability. The most commonly used materials include Carbon (C), Silicon Carbide (SiC), Ceramics (Cer) and Tungsten Carbide (TC). The choice depends on whether you are pumping thin liquids, abrasive media or chemically aggressive products. 

Are you unsure about which one to choose? We have made a guide to help you make the right choice. You can also learn more about the different types of gaskets that help complete the mechanical seal. 

If we are to help you find a new mechanical seal that fits your equipment perfectly, we need to know the axle diameter. This is one of the most important technical specifications to ensure that the seal fits tightly and functions correctly during operation. Once you have this measurement ready, we can quickly identify the correct mechanical seal that matches your pump or mixer. 

Our range includes mechanical seals for all kinds of pump types and models. In the video, we take a closer look at seals compatible with Alfa Laval pumps – including the LKH series and FM variants with and without a flushing function. However, we also offer solutions for equipment from suppliers such as APV, Fristam and Johnson. This gives you the flexibility to choose the seals that best suit your process. 

We’ve seen this mistake before: testing or running the pump without product. It may be tempting to carry out a quick rotation check after installation, but this is where damage often occurs, before production has even started. 

We call this ‘running the pump dry’, and the consequences are severe. Without a liquid to lubricate and cool the sliding surfaces, the friction generates extreme heat within seconds. This leads to thermal shock, where the precision-ground surfaces either crack or fuse together. You risk a completely damaged seal that needs replacing immediately, causing unnecessary downtime and extra costs. 

Our clear recommendation: Always ensure that the pump is filled with the medium, or that the seal is connected to the flushing function (if applicable), before the axle rotates. It is a small detail in the start-up procedure that makes all the difference to your operational economy. 

Are you unsure which mechanical seal is best suited to your plant? Then get in touch – we’re happy to discuss your needs and help you find the solution that matches both your process and requirements. Call +45 7020 0422 or send an email to inquiry@alfotech.eu. Together, we’ll find the right solution for your production.