Balanced and unbalanced mechanical seals are two types of sealing solutions used in rotating equipment.
They differ in their design, pressure handling capabilities, and application suitability.
This blog post will explore the key differences between these two seal types.
It will help you understand when to use each type for optimal performance.
What Is the Balance of Mechanical Seals
The balance of mechanical seals refers to the design that equalizes pressure on both sides of the seal faces. Balanced seals have equal pressure on the inboard and outboard sides. This reduces heat generation and wear, allowing for higher operating pressures and speeds.
Unbalanced seals have higher pressure on the inboard side, which can limit their operating range. However, they are simpler and less expensive than balanced seals.
What Is Balance Ratio
Balance ratio is a measure of the pressure distribution on the seal faces in a mechanical seal. It is calculated by dividing the area of the seal face exposed to the sealed fluid pressure by the total area of the seal face.
A balance ratio of 1.0 means the seal is perfectly balanced, with equal pressure on both sides. Lower balance ratios indicate a more balanced seal, while higher ratios indicate an unbalanced seal.
Balanced seals usually have balance ratios ranging from 0.65 to 0.85. This means that 65-85% of the seal face area is exposed to the sealed fluid pressure, while the remaining area is exposed to the atmospheric pressure.
Unbalanced seals have balance ratios around 1.2. This indicates that the entire seal face area is exposed to the sealed fluid pressure, resulting in a higher net closing force on the seal faces.
What Are Balanced Seals
Balanced seals are mechanical seals designed to equalize pressure on both sides of the seal faces. This is achieved by exposing the backside of the rotating seal face to the same pressure as the process fluid. Balanced seals can handle higher pressures compared to unbalanced seals.
The balanced design reduces the net closing force acting on the seal faces. This allows for lower face loading and improved performance. Balanced seals are commonly used in applications with high pressures or where low face loading is desired.
What Are Unbalanced Seals
Unbalanced seals are mechanical seals where the closing force is not equalized on both sides of the seal faces. In an unbalanced seal, the process fluid pressure acts on the entire area of the rotating seal face. This results in a higher net closing force compared to balanced seals.
The higher closing force in unbalanced seals leads to increased face loading and friction. Unbalanced seals are typically used in applications with lower pressures or where the increased face loading is acceptable. They have a simpler design compared to balanced seals.
Differences between Balanced and Unbalanced Mechanical Seals
Pressure Distribution
- Balanced seals: Pressure is distributed evenly across the seal faces, reducing the net hydraulic closing force.
- Unbalanced seals: Pressure is concentrated on a smaller area of the seal faces, resulting in a higher net hydraulic closing force.
Spring Force
- Balanced seals: Require lower spring force to maintain proper face contact due to the reduced hydraulic closing force.
- Unbalanced seals: Require higher spring force to counteract the increased hydraulic closing force and maintain proper face contact.
Seal Face Wear
- Balanced seals: Experience less wear on the seal faces due to the reduced closing force, resulting in longer seal life.
- Unbalanced seals: Experience higher wear on the seal faces due to the increased closing force, which can lead to shorter seal life.
Pressure Handling Capacity
- Balanced seals: Can handle higher operating pressures due to the even pressure distribution across the seal faces.
- Unbalanced seals: Have a lower pressure handling capacity due to the concentrated pressure on a smaller area of the seal faces.
Applications
- Balanced seals: Commonly used in high-pressure applications, such as pumps handling high-pressure fluids or gases.
- Unbalanced seals: Often used in low to moderate pressure applications, such as pumps handling low-pressure fluids or in less demanding environments.
Cost
- Balanced seals: Generally more expensive due to their more complex design and additional components required for pressure balancing.
- Unbalanced seals: Typically less expensive due to their simpler design and fewer components.
In conclusion
Balanced and unbalanced mechanical seals each have their own strengths depending on the application. Balanced seals work well for high-pressure systems, while unbalanced seals are simpler and cost less for lower-pressure uses.
Contact our seal experts today to discuss the optimal seal configuration for your specific equipment needs. We’re here to help you maximize performance and reliability.
