Guide: How to Prevent and Fix Leaking Pump Seals

Why do pump seals leak ? What amount of leakage is normal, and what indicates a pump seal failure ? In finding the answer, you will also find the best pump seal solution to fix your pump’s leaking seals.

The whole purpose of pump seals – either mechanical seals or packing seals – is to contain the pressure of the pumping process and withstand the friction of the pump shaft rotating to prevent the pump from leaking. However, both positive displacement pumps and centrifugal pumps can be plagued by leaking seals.

Problems Caused by Leaking Seals

Leaking seals are one of the main pumping problems. A pump seal leak leads to wasted product, cleaning hassles, and unnecessary expense. Leaking seals are the biggest reason for pump downtime, and the largest share of pump repair cost can be attributed to mechanical seals. Solving the problem of leaking mechanical seals improves uptime and reduces overall operational costs.

Causes of Mechanical Seal Failure

Understanding why mechanical seals leak is a good first step towards being able to address the causes of mechanical seal failure and prevent a pump mechanical seal leak in the future. Common causes of pump mechanical seal leaks include:

Wear down of the seal material. All parts of the seal need to be resistant to the chemical and physical demands of the pumping process or the working life of the seal will be reduced, and eventually may cause seal failure. Bearing wear naturally occurs over the lifetime of a mechanical seal. However, contamination within the seal support system or internal to the pump can be caused by reduced by changing to a fluid that is more effective at keeping contaminants from the pump seal, or by upgrading to a seal with high quality bearings.
Dry running. Dry running usually happens when a pump is restarted after maintenance. Pump seals need lubrication around the shaft to prevent friction and heat. When a pump is run dry, it can quickly result in heat cracks or blisters, and melted or burned seals. These damaged pump seals leak fluid due to pressure, and they can even shatter if the right conditions are met.
Shocks and vibrations. Vibrations caused by improper alignment, pump imbalance, and operating the pump too far from the Best Efficiency Point (BEP) on the performance curve can damage seals and shorten their lifespan.
Improper installation. Mechanical seal installation instructions should be followed exactly, because errors can easily damage the seals, and starting the pump with an incorrectly installed seal can damage other parts of the pump as well. Some of the possible installation errors include shaft misalignment, dirt on the face of the seal, or hammering couplings into the shaft.
Changes in operating parameters. Mechanical seals often leak because something changed about the operating conditions, such as pressure in the seal chamber, temperature around the shaft seal, pumped medium, speed, and shaft seal dimensions.
Poor lubrication. If lubrication is poor, there is no liquid around the seal and it will undergo excess friction, which increases temperature in the pump and can burn seal parts.
Pumping slurry. Slurries are particularly likely to damage a mechanical seal by clogging the flexing parts of the seal, eroding the impeller, or causing wear on rotating elements.
Inadequate flush plan. Mechanical seals require a flush plan. If the flush plan is nonexistent, dewatered product and contaminants build up, causing either erosion on the seal or excessive heat.

Centrifugal Pump Seal Types

Historically, centrifugal pumps have usually been designed with packing seals. Packing seals are packed with a lubricated fibrous material that came into direct contact with the shaft, so flush water is necessary to cool and lubricate the shaft. Flush water has to be directed away from the process to prevent contamination, and care has to be taken to protect the bearing box from flush water that contaminates the oil, as well as to prevent the safety problem of water pooling on the floor.

Mechanical seals may have a higher initial cost, but they often save a great deal of operational cost depending on how much flush water a packing seal pump consumes.

When choosing a mechanical seal for centrifugal pump operation, you will come across these types:

Balanced and Unbalanced Seals

Balanced Seals have a system where forces acting on both faces are balanced, so there is more even lubrication of seal faces. Balanced seals have a higher cost than unbalanced seals, and they tend to last longer. Unbalanced seals show less leakage and are more inexpensive, but they have a lower mean time between failures and are not recommended for high pressure applications.

Pusher and Non-Pusher Seals

Pusher seals use one or more springs to maintain sealing forces, while non-pusher seals use elastomeric or metal bellows. Pusher seals can be used at very high pressure applications, but they have an elastomeric seal that can wear. Non-pusher seals are ideal for medium/low pressure and high temperature or dirty applications.

Conventional and Cartridge Seals

Conventional mechanical seals are installed as components. Cartridge seals have all the seal elements contained within a single assembly, so they are quick to install and reduce the chance of installation errors.

Positive Displacement Pump Seal Types

Many industrial processes still use a packing seal for positive displacement pump applications. Packing seals, which are designed to allow some controlled leakage, can be a reliable method of preventing excessive leaks. However, stricter standards in industries like food processing are reducing the amount of acceptable leakage.

For some existing Viking Pump models that require positive displacement pump seal replacement, an upgrade to a Viking Pump O-Pro seal reduces the problem of leaky seals for difficult-to-seal applications like chocolate, honey, asphalt, or adhesives.

Patented O-Pro® Seals are designed with a series of O-rings that create both a seal and a lubrication chamber. There are three O-Pro seal types available: O-Pro® Barrier seal that acts as both a seal and bracket bushing, while the O-Pro® Cartridge & Guard seals are simple retrofit options.

Best Ways to Prevent Seal Failure

The tendency of mechanical seals to leak depends on several factors that may not be entirely related to design, which means it is possible to reduce mechanical seal failures.

Choose the right mechanical seal

Choosing the right mechanical seal is critical to prevent pump seal leaks. Consider both the normal operating conditions and the application for the seal. Also take into account the possibility of any use outside normal operating conditions.

If a seal keeps failing in the same way, consider installing an updated pump seal design to mitigate the issue. Often a newer seal design can offer better centrifugal pump efficiency and a variety of seal face materials engineered to withstand harsher chemicals and processes than the original seal.

Use specialized seals when necessary, like seals designed to pump slurry. Flexaseal heavy duty interchangeable slurry cartridge seals have features like reverse pressure capability, non-clogging multi-springs, rugged seal drive operation, and hydraulically balanced faces to respond to challenges of pumping slurry.

Make sure the seal is installed correctly

Following the manufacturer’s instructions will help prevent installation damage to O-rings or seal faces, which is a common reason why mechanical seals leak. It’s not uncommon to forget to tighten set screws before removing setting clips, or to use piping connections improperly.

One type of seal that helps save time and avoid the expense of installation errors is a Flexaseal single cartridge mechanical seal.

Avoid dry running and excess heat generation

Dry running reduces seal life by generating too much heat between seal faces. This often occurs during startup when the seal chamber isn’t vented properly or the pump is flooded.

For batch run operations like tank unloading where operators may often neglect to shut the pump down, seals such as the Flexaseal Dual Cartridge Mechanical Seal are designed to run dry with gas lubrication. By using nitrogen as a lubricant, they contain no barrier fluid and can retain 100% product purity.

Store mechanical seals properly

Because seal components can be delicate, manufacturers often stipulate how they should be stored, and for how long. Usually a clean, humidity-controlled, temperature-controlled environment is required, and the seals need to be rotated occasionally to prevent face lock.

Older seal designs provided the best solutions at the time of installation, but today’s designs and material improvements provide far more reliable, lasting seals, and may offer optional components and upgrades.

Seal failures that occur once are likely to occur again in the same manner if nothing is changed.

When deciding if a pump seal needs to be replaced or upgraded, pay attention to seals that have a repair history that shows declining efficiency or longevity. If your pump has trouble with leaking seals, or if your pump’s operating parameters will be changing, Carotek can assist with analysis of the problem and next steps to find the best pump seal solutions.

Watch how we solved one Carotek customer's leaking seal problem.

In some circumstances, a Seal Pot should be considered to prevent any type of fluid leaks in your pump system. Carotek manufactures our own line of Seal Pots, Pressure Vessels and Seal Support Systems , so we can customize the right sealing system for your application.

Featured Pump Articles