What are the disadvantages of a double mechanical seal?

As a supplier of double mechanical seals, I've seen firsthand the many benefits these seals offer. They're great at preventing leaks, handling high pressures, and lasting a long time in tough conditions. But like anything, they've got their downsides. In this blog, I'm gonna break down some of the disadvantages of double mechanical seals.

High Initial Cost

One of the biggest drawbacks of double mechanical seals is the high upfront cost. Compared to single mechanical seals, double mechanical seals are way more expensive. You're not just paying for the two sets of sealing faces, but also for the extra components like the seal chamber, flushing system, and monitoring devices. For example, if you're looking at a Johnson Pump Mechanical Seal, the price can be significantly higher than a single seal. This high cost can be a real barrier for small businesses or those on a tight budget. They might end up going for a cheaper alternative, even if it means sacrificing some performance.

Complex Installation

Installing a double mechanical seal is no walk in the park. It's a lot more complex than installing a single seal. You need to have a good understanding of the equipment and the sealing system. There are more parts to handle, and the alignment has to be just right. If the installation is done incorrectly, it can lead to all sorts of problems, like leaks, premature wear, and even equipment failure. You might need to hire a professional installer, which adds to the overall cost. And even then, there's always a risk that something could go wrong during the installation process.

Maintenance Requirements

Double mechanical seals require more maintenance than single seals. You've got to keep an eye on the flushing system, the seal faces, and the monitoring devices. The flushing system needs to be properly maintained to ensure that the seal faces are kept clean and cool. If the flushing fluid gets contaminated or the flow rate is too low, it can cause damage to the seal faces. You also need to regularly inspect the seal faces for wear and tear. If you notice any signs of damage, you've got to replace the seals right away. And don't forget about the monitoring devices. They need to be calibrated and tested regularly to make sure they're working properly. All this maintenance takes time and money, and it can be a hassle for some users.

Space Constraints

Another disadvantage of double mechanical seals is that they take up more space than single seals. In some applications, space is at a premium, and there might not be enough room to install a double seal. For example, in a small pump or a compact piece of equipment, there might not be enough clearance for the additional components of a double mechanical seal. This can limit the use of double seals in certain applications. You might have to look for a more compact sealing solution, even if it doesn't offer the same level of performance as a double seal.

Potential for Seal Failure

Even though double mechanical seals are designed to be more reliable than single seals, they're still not immune to failure. There are several factors that can cause a double seal to fail. One of the most common causes is improper installation. As I mentioned earlier, if the seals are not installed correctly, it can lead to leaks and premature wear. Another cause of failure is contamination. If the flushing fluid or the process fluid gets contaminated, it can damage the seal faces. And then there's the issue of thermal expansion. If the temperature of the equipment changes too quickly or too much, it can cause the seal faces to expand or contract, leading to leaks. When a double seal fails, it can be a real headache. You've got to shut down the equipment, replace the seals, and get everything up and running again. This can result in significant downtime and lost productivity.

Compatibility Issues

Double mechanical seals need to be compatible with the equipment and the process fluid. If they're not compatible, it can cause all sorts of problems. For example, if the seal material is not resistant to the process fluid, it can corrode or degrade over time. This can lead to leaks and premature failure of the seal. You also need to make sure that the seal is compatible with the operating conditions, such as temperature, pressure, and speed. If the seal is not designed to handle the specific conditions of your application, it might not work properly. And finding the right seal that's compatible with your equipment and process fluid can be a challenge. You might have to do a lot of research and testing to find the best solution.

Higher Energy Consumption

Double mechanical seals can also consume more energy than single seals. The additional components and the flushing system require more power to operate. The flushing pump, for example, needs to be running continuously to provide the necessary flow of flushing fluid. This can increase the energy costs of the equipment. In today's world, where energy efficiency is a top priority, this can be a significant drawback. You might need to look for ways to reduce the energy consumption of the double seal, such as using a more efficient flushing pump or optimizing the flushing system.

Despite these disadvantages, double mechanical seals still have their place in many applications. They offer superior performance and reliability in certain situations, especially where leakage prevention is critical. If you're considering using a double mechanical seal, it's important to weigh the pros and cons carefully. Make sure you understand the potential drawbacks and are willing to deal with the additional costs and maintenance requirements.

If you're interested in learning more about our double mechanical seals, like the M7n Mechanical Seal or the Bellow Mechanical Seal, feel free to reach out to us. We'd be happy to discuss your specific needs and help you find the right sealing solution for your application. Let's talk about how we can work together to meet your requirements.

References

• Mechanical Seals Handbook, John A. Neale
• Sealing Technology for Rotating Equipment, John M. Allred