6 Points of Seal Failure and How to Avoid Them

6 Points of Seal Failure and How to Avoid Them

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Seals are crucial in maintaining the functionality of rotary systems. However, various factors can impact their performance. Understanding these elements helps in selecting the optimal seal, thereby reducing the risk of failure.

Installation

The lip of a seal is essential in minimizing wear. Proper lubrication under the seal lip ensures low friction while preventing leakage. Modern seal lips are effective but require careful installation to avoid damage.

Seal lips can be delicate, particularly those made of rubber or polytetrafluoroethylene (PTFE). Incorrect installation angles or improper conditions can damage them. Additionally, their small size makes them easy to install backward.

To prevent installation issues, ensure seals are aligned correctly and not tilted. Verify that the seal lip is appropriate for the system, facing the right direction, and aligned with the shaft's rotation.

Contamination

Seals in rotary systems are often positioned near bearings, which can attract debris leading to further contamination and damage. Changing the system fluid might not fully resolve this issue as contaminants can settle around the seal.

To mitigate contamination risks, clean all system components thoroughly before assembly, particularly removing small metal debris from machining. Regularly check and flush the system oil if contamination levels are high. Replace seals whenever bearings are changed to avoid potential failure from prior exposure to contaminants.

Friction

Excessive heat in rotary systems can cause fluid breakdown, damage shaft material, and degrade the seal lip. Solutions include using higher temperature-resistant materials, such as PTFE, hardening the shaft, or using higher viscosity fluids. Increasing lubricant quantity and employing heat-conductive housings can also help dissipate heat.

Mating Surfaces

A well-finished shaft is critical. Avoid burrs or sharp edges to prevent seal damage. Microscopic screw patterns from traditional grinding can create unwanted fluid movement. Use plunge grinding to eliminate angles in machining marks.

Match the shaft's surface finish to the seal material. Too rough a finish accelerates wear, while too smooth a finish reduces lubrication retention, increasing friction.

Shaft Dynamics

Any irregular shaft movement can harm seals. Poorly aligned bearings or shafts cause uneven compression, leading to elevated wear and potential leakage. Ensure precise design, machining, and bearing positioning to prevent uneven seal compression.

Condition of Fluid

Regular fluid checks are necessary due to minimal fluid interchange near rotary seals. Fluid conditions can deteriorate, leading to issues like air bubbles, increased moisture content, and low oil levels. Poor fluid conditions can accelerate bearing wear, causing misalignment and debris that damages seals.

3 Common Reasons for Seal Failure

Seal failures can significantly disrupt operations. Understanding common causes helps extend seal life and protect equipment.

1. Improper Installation

Proper installation prevents initial seal damage. Ensure lubrication, clean surfaces, and use custom tools for crossing features like threads. Chamfers should facilitate smooth transitions.

2. Seal Glands

Machined seal glands should have proper lead-in chambers and radii. Ensure concentricity and minimize extrusion gaps. Excessive extrusion risks seal failure.

3. Operating Conditions

Aggressive chemicals, temperature fluctuations, and over-pressurization can degrade seals. Communicate all operating conditions to engineers to design optimal seals.

Questions to Consider in Seal Design

• Installation: Are all surfaces considered? Are lead-in chamfers sufficient?
• Seal Glands: Are glands designed per manufacturer recommendations?
• Operating Conditions: Are all environmental factors communicated, including temperatures, pressures, and fluid compositions?

Determining Failure Modes

When seals fail, various indicators help diagnose the root cause. Qualified engineers should inspect failed seals for issues like grooving, swelling, deterioration, hardening, scarring, wear, extrusion, and fractures.

Maximizing Seal Performance

Proper sealing improves equipment reliability, maximizes capacity, optimizes maintenance, reduces wear, and extends equipment life.

Focusing on installation, surface finish, and operating conditions will enhance seal performance and overall equipment efficiency.

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