5 Ways to Extend the Service Life of Mechanical Seals

An often forgotten critical component in a centrifugal pump system is the mechanical seal, which prevents liquid from leaking into the surrounding environment. Mechanical seal leaks due to improper maintenance or operating conditions beyond expectations can cause hazards, regulatory issues, health issues, and even EPA issues. It is important to incorporate various engineering practices and operating conditions to ensure proper operation and service life of the mechanical seal, thereby preventing leaks and the resulting downtime or safety hazards.

The following measures can be taken to extend the service life of the centrifugal pump mechanical seal.

• 1. Understand the operating conditions

Pressure, temperature and speed are all factors that can cause seal wear or increased leakage. Understanding the operating conditions will help you better select the appropriate mechanical seal (and its supporting system). Under fixed operating conditions, a mechanical seal may perform well, but if system variables are introduced, they can have a dramatic effect, reducing the durability of the seal. For continuous operation with more stable conditions, the published limits of what the seal can withstand are more accurate. In unstable conditions, these limits are less accurate.

A combination of process variables creates different operating conditions where seals may need to be adjusted, such as vaporization, freezing, or extreme heat that needs to be dissipated. Applications operating at higher pressures, higher temperatures, faster speeds, and denser pumped fluids make it more difficult to maintain pump efficiency. If your fluid transfer process is more difficult, having a mechanical seal that is more robust and can withstand changes in operating conditions may be the key to minimizing maintenance downtime.

• 2. Understand the durability of the sealing surface in liquid

In most cases, the pumped liquid is the lubricant for the mechanical seal. Depending on the application, the liquid is susceptible to temperature and pressure changes. Similar to the operating factors, the liquid is the main variable and its physical and chemical states vary greatly and need to be understood. Depending on the temperature, pressure and chemical compatibility, the liquid varies in density, purity, volatility, toxicity and can even be explosive.

Higher seal face pressure and deflection capabilities reduce the chances of replacing or repairing the seal. Susceptibility to damage can be reduced by choosing the right combination. Hard/hard mechanical seal faces are better for dirty fluids, but are more susceptible to damage if the fluid film is lost. Hard/soft mechanical seal faces can remain sealed longer after the fluid film is gone until the seal face is damaged. It is important to understand the extreme conditions that the pump system will encounter during the application and how this will affect the fluid state and how the seal can maintain the expected performance.

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• 3. Understand the causes of seal surface wear

Excessive leakage is often a symptom of worn seal faces. The pump may also have other more serious problems, such as damaged bearings or bent shafts.
If the wear is due to frictional contact, the friction edges of the seal will show signs of physical damage, such as grooves or even chips. Some seals also require flushing the system to remove the heat generated. If this process is interrupted or stopped, serious problems may occur.

• 4. Reduce vibration

Try to run the pump at or near the BEP (Best Efficiency Point). Departure from the BEP may cause cavitation in the pump, which can cause vibrations that damage the seals. Running at maximum flow can be fatal to the pump. Excessive vibration can cause degradation of parts within the seal (such as O-rings, bellows, polymers or wedges) or metal parts (such as springs, drive pins or set screws).

• 5. Proper flushing/lubrication

Mechanical seals rely on a film of liquid between the seal faces to reduce heat and friction. In most cases, the pumped liquid provides lubrication as it contacts the seal faces. Do not run a mechanical seal dry (without liquid in the seal chamber) to maintain the seal. Install a dry-run monitor or flow sensor to sound an alarm when there is not enough liquid in the system. It is for this reason that continuous applications often provide a better guarantee of mechanical seal reliability than intermittent applications.

Overall the average life of a mechanical seal is at least two years. Obviously, as mentioned previously, this depends greatly on the variables involved, the conditions and the operating limits. Understanding your pumping system and how it operates, as well as what to look out for when problems arise, can go a long way toward extending the life of your mechanical seal. Selecting the right seal can be a time-consuming and complex process, but a professional seal manufacturer has knowledgeable experts who can provide the right sealing solution for your application and help your system operate at peak efficiency.