Mechanical seal failure is one of the primary causes of pump downtime. Seals are exposed to a wide variety of conditions, including equipment and operations conditions, operational environment, and seal set-up. When operational conditions change, or if the seal is not suitable for the application, the seal is generally the first part of the pump to fail, causing leakage and premature seal failure. In this article, we look at seal design and how to prevent frequent maintenance and replacement of seals.
There are a number of elements of seal design that can lead to increased leakage, including the type of liquid being pumped, the environmental control used, and the seal design chosen for the application.
The type of liquid being pumped helps determine which seal design and materials of construction are the most appropriate.
All parts of the mechanical seal need to have adequate resistance to the liquid being pumped to prevent seal leakage and extend its lifecycle. All elements of the liquid, including pH, temperature and pressure can affect mechanical seals. If the mechanical seal does not have an appropriate level of resistance it will quickly degrade and malfunction.
For example, seal face design and materials are critical in applications where an abrasive product is being pumped to help prevent excessive wear to the primary seal components due to erosion which can lead to increased leakage.
Another aspect of mechanical seal design and seal set-up to consider is the use of an appropriate environmental control or flushing system. Recommended environmental controls are provided by the manufacturer and supplier, and are an important part of the design and installation. Environmental controls are tailored to suit different applications and without one, contaminates build up, causing excessive heat or erosion on the seal, leading to increased leakage and failure.
Selecting the right design
There are a large array of designs and features on the market to suit different applications, including stationary spring and rotary spring features, single and double cartridge designs, split cartridge seals, cassette designs, non-clog features, balanced face design, component seal and non-contacting lift-off designs.
According to Jason Lynch, Director at FITT Resources, all of these have their own benefits for certain applications but it’s important to seek expert advice when it comes to choosing what is best for individual projects.
“When selecting a seal it’s important to talk with the seal supplier to determine the design that best establishes a good balance for the individual operating conditions,” Mr Lynch said.
“Things to consider when choosing the design include operating conditions of the pump, pump design, and products being pumped to existing plant standards such as API and environmental hazards or a standardisation program.
“Mechanical seals are considered best practice in most industries but there is still a problem of excessive leakage and seal failure if users don’t understand what can cause it. If users are experiencing a high level of leakage and seal failure, it is important to take a look at the equipment and operation conditions, as well as the seal design, because these could be part of the problem.”