Anyone in the maintenance field who has repaired a pump or gearbox knows the one component that always seems to get replaced during a rebuild is the lip seal. It usually is damaged when being extracted or during disassembly. Perhaps the lip seal is the reason the piece of equipment was pulled from service due to leakage. Regardless, the fact remains that lip seals are vital machine components. They keep oil or grease in and help keep contaminants out. Lip seals seem to be on almost every piece of plant equipment, so why not take the time to learn how to correctly select and install them.

70%

of lubrication professionals say their plant uses lip seals to control contaminant ingression, based on a recent survey at MachineryLubrication.com

Purpose of Lip Seals

The primary purpose of a lip seal is to exclude contaminants while retaining lubricants. By nature, lip seals function by maintaining friction. They can be used in a variety of applications from slow-moving equipment to high-speed rotation and in temperatures from below freezing to more than 500 degrees F.

To be effective, a lip seal must maintain proper contact with its rotating counterpart. This will be influenced by proper selection, installation and care of the seal once it is installed. I’ve often seen a new lip seal start to leak as soon as it was put into service. This typically is due to improper installation. Other seals will leak initially but then stop leaking once the seal material has seated to the shaft.

Selecting a Lip Seal

Maintaining functional lip seals begins with the selection process. When choosing a material, you must consider the operating temperature, the lubricant in use and the application. The most common lip seal material is nitrile (Buna-N). This material functions well at temperatures of minus 40 degrees F up to 275 degrees F. Nitrile lip seals cover most applications in industry from new equipment to replacement seals. They have excellent resistance to petroleum oils, water and hydraulic oils, but what really sets these seals apart is their low cost.

Another affordable option is Viton. Its temperature range is minus 40 degrees F to 400 degrees F, depending on the specific compound. Viton seals provide good resistance to petroleum oils and can be employed with gasoline and transmission fluid.

Other seal materials that can be used with petroleum oils include Aflas, Simiriz, carboxilated nitrile, fluorosilicone, highly saturated nitrile (HSN), polyurethane, polyacrylate, FEP and silicone. All of these materials have specific applications and precise temperature ranges. Be sure to take into account the process and environment before selecting a seal material or making a switch, as the correct material can prevent a costly failure.

Lip Seal Construction

Once the seal material has been selected, the next step is to consider the seal’s construction. In the past, a simple lip seal consisted of a leather strap on a wheel axle. Today’s lip seals have multiple parts that affect how the seal performs. There are various contacting patterns as well as non-spring and spring-loaded seals. A non-spring seal generally will be less expensive and be able to retain viscous materials like grease at slow shaft speeds. Typical applications include conveyors, vehicle wheels and greased components. Spring-loaded seals are typically used with oils and can be found on a wide range of equipment.

Lip Seal Installation Checklist

• The elastomer is not damaged (no nicks, scratches, cuts, etc.)
• The case is not damaged (no nicks, cuts, dents, etc.)
• The garter spring is properly placed (if used)
• Wipe the seal and shaft of any debris
• The assembly lube is compatible with the lubricant in operation
• The case is of the proper specification
• The elastomer is of the proper specification
• The lip seal is pointing in the correct direction
• The shaft is free of defects (no nicks, scratches, grooves, etc.)
• The bore is free of defects (no nicks, debris, roundness, etc.)
• There is adequate ventilation of equipment when stored or in operation
• Proper installation tools are used to avoid damaging seals
• Equal pressure is applied during installation to ensure the seal is not cocked

Installation

After the seal material and construction have been chosen, the lip seal must be installed correctly for it to perform. There are a number of products on the market dedicated to this single task. Most look like a socket set that will position the seal squarely into its bore. These tools can work well if selected carefully, but most off-the-shelf versions aren’t as effective, especially when a shaft is already installed.

For these instances, I prefer to use a pipe that is large enough to slip over the shaft and makes good contact with the lip seal’s outer shell. If you can find something that catches the outer casing, you can prevent damaging the inner metal ring that attaches to the lip seal material. Just be sure to set the seal in straight and at the correct depth. Failure to properly set the seal perpendicular to the shaft can cause immediate leakage.

If you have a used shaft, it likely has developed a wear ring where the old lip seal was placed. You should never set the contact patch to a previous contact point. If this is unavoidable, there are products that you can slip over the shaft to help with the damaged surfaces. This is usually quicker and more cost effective than replacing a shaft. Keep in mind that the lip seal will need to be resized for the added sleeve.

When installing lip seals, make certain the job is done correctly. I’ve seen guys install seals with a punch so they wouldn’t have to take the extra time to locate the right tool. One wrong thump from a hammer can tear sealing material, puncture the seal casing or push the seal through the housing.

Always take time when installing lip seals, and lubricate the shaft and seal adequately to prevent tearing or sticking. Also, verify that the lip seal is the correct size. There must be an interference fit in the bore and on the shaft. Not having the proper size can result in the seal rotating on the shaft or becoming dislodged from the equipment.

Lip Seal Inspection Checklist

• Check for cracked or deteriorated elastomer
• Check for case damage
• Check to see if the breather is plugged
• Check equipment for excessive temperatures
• Check for oil leaks around the lip seal

Maintaining Lip Seals

To help your lip seals stay as healthy as possible, you must keep your oil clean, cool and dry. Any contamination in the oil will get into the contact patch and deteriorate the shaft and elastomer. Likewise, the hotter the oil becomes, the more wear and tear will be exerted on the seal. Lip seals should also be kept as clean as possible. Painting over a seal or having dirt built up around it can create excessive heat and quickly degrade the elastomer.

Failure Causes

If you’ve ever pulled out a lip seal and seen a groove cut into your shaft, this is probably due to particle contamination. Without good breathers, all the dust and dirt that gets into your equipment can destroy not only your bearings and gears but also your shafts and lip seals. Of course, it is always better to exclude contaminants than to try to remove them. Too tight of a fit between the lip seal and the shaft can also create a groove.

Excessive temperature is the leading cause of seal failures. As temperatures rise, the lubricating film becomes thinner, resulting in dry running conditions. Elevated temperatures can also lead to the elastomer cracking or blistering. Nitrile seal life decreases by a factor of two for every increase in temperature of 57 degrees F.

The oil level can be another factor in a lip seal’s lifespan if it is too low. In this situation, the seal will eventually become hard and not be able to follow the shaft, resulting in leakage.

Cold temperatures can cause seal embrittlement. Selecting the proper lubricant and seal material can help in these colder environments.

Seals may also fail due to shaft runout. This can be caused by misalignment, shaft imbalance and manufacturing inaccuracies, to name a few. Different elastomers will tolerate varying amounts of runout. Adding a garter spring will help with any runout that can be measured.

Excessive pressure is another potential cause of lip seal failure. If you’ve ever walked past a pump or gearbox and noticed oil leaking out the seal, the sump has somehow overpressurized and leaked to the point of least resistance. This can be attributed to clogged breathers or non-vented sumps. Applications with higher pressures should employ a special seal design.

How to Inspect a Lip Seal

Among the things to look for when inspecting lip seals include deteriorated or cracked elastomer. This is a telltale sign that heat is an issue. Also, verify that the lip seal is still in place. I’ve seen a few pumps that had the wrong seal installed. Upon startup, the vibration and movement caused the seal to come out of the bore and spin on the shaft.

Any oil leaks around the seal should be a red flag to investigate further. Worn seals can cause leakage, plugged breathers or damaged bearings that allow radial motion.

When analyzing any lip seal failure, look at the seal, shaft and bore. While inspecting the shaft, you typically will see a contact or wear zone where the lip seal was riding. This will appear as a black scuffmark where the elastomer has transferred to the shaft.

Remember, in order to keep your lip seals in good operating order, you must maintain the sump. Cover all seals before painting, keep the oil at the proper level, make sure oil coolers are functioning correctly, and select the right seal design and material. If you are proactive in your approach to rebuilding and installing equipment, you can give your lip seals and machinery a fighting chance at survival.

About the Author

Oil seals (also known as rotary seals or shaft seals) cover a wide range of applications ranging from domestic equipments to automotive and power plant machinery, industrial pumps, gas and aircraft turbines and compressors.

If yours is a modern system, the surface speed can go up to 30 m/s and operating temperature can be as high as 250 degree Celcius. For these type of oil seals, our general purpose high performance oil seals can be employed. When the speed is increased up to 90 m/s, the lip will be produced using PTFE based compound to reduce heat generation. For high pressure applications, we offer a wide range of oil seal profile made using PTFE based compounds.

Here at Advanced Sealing Devices, we make and design reliable oil seals for your demanding tasks. If the oil seal is not selected properly, then even a few percents of leakage can be inconvenient and incur expenses to a large number of users, as well as cause environmental pollution. Note that the oil seal is not only to seal lubricating oil, it can also be used to seal other fluids such as water, foodstuff and chemicals. We understand that the reliability and reputation of your system depends on the well functioning of these oil seals.

Standard oil seals operate in a splash environment with no pressure or little pressure as low as 0.3 – 0.5 bars. If you have a higher pressure requirement, contact us and we can provide you with a different type of oil seal design. If a standard type of oil seal is used in a high pressure situation, lip distortion and wear will occur. This will shorten the lifespan of the oil seal and create unnecessary downtime. If your housing tolerances are not controlled as closely as standard housings, we can make the outer casing of oil seals with special profile so that the oil seals can seat properly in your housing before the assembly press tool is removed.

If you application is such that the lubricating liquid is not continuously available, or the operating temperature, fluid compatibility, the speed and pressure are of a more demanding nature, then we can make oil seals using stainless steel outer casings with various pure and filled PTFE lips (type ASD SS-PTFE). This type of oil seal is now widely used by our customers in the automotive and transmissions industry. A stainless steel casing with a PTFE lip oil seal will support more highly rated machinery and allow longer oil change intervals. Our ASD SS-PTFE type is particularly suitable for dry running application, for example, an engine may run dry for some period during startup until oil splash is available especially after a long period of storage or transportation. There are certain design aspects that are required in your system before using our ASD SS-PTFE type oil seal; contact us and we will advise you on this aspect. The following are some examples of stainless steel oil seals we make for our customers.

Maintenance Tips to Extend the Lifetime of Mechanical Seals

Some tips and best practices can help you extend the lifetime of your mechanical seals. Mechanical seals are vital for rotating equipment that require peak performance such as pumps, compressors, and any equipment with rotating shafts. These seals have few issues when a proper inspection and maintenance plan is followed. However, if the equipment and its seals are not regularly maintained, this will lead to visible leaks causing significant downtime and, in some cases, injury to employees. To avoid this, following some best practices can you can extend the lifetime of your units’ mechanical seals and the whole system.

How to Improve the Lifetime of Industrial Pumps & Mechanical Seals

Unplanned production downtime can be a nightmare for operations managers, which is why the maintenance team is critical when looking at improving the lifetime of seals. The plan should include a full industrial pump service focusing on more than just the specialized equipment. We recommend  getting in touch with an expert maintenance team to develop a plan for the entire system. Pipes, valves, and other areas are just as important for the manufacturing plant’s operation.

Best Practices for Pump & Seal Maintenance to Extend the Lifetime of Your Mechanical Seals

To ensure proper operation, several best practices should be followed.

Don’t Let the Seal Run Dry

The most important consideration to avoid multiple mechanical seal repairs is never let the seal dry out. When there is no liquid between the seal faces to cool them down, heat will build-up resulting in dry seals. If this isn’t monitored and seals dry out completely, they can crack and cause catastrophic seal failure. One way to ensure your seals don’t run dry is to install a dry run monitor connected to an alarm or notification setting. This monitor will alert employees when a seal has insufficient lubrication to function properly.

Avoid Excessive Vibration

If a pump system operates outside its Best Efficiency Point (BEP), recirculation and cavitation can lead to vibration moving through the impeller; the pump shaft; and ultimately, the mechanical seal. Vibration can also be caused by system degradation and wear through imbalance. One main cause for imbalance is when pumps and industrial gearboxes are used outside their intended design specifications.

Correct Lubrication

For a seal to work properly, it relies on a cooling fluid film between seal faces. This fluid minimizes wear and friction, guaranteeing reliable performance and a pump operating within its BEP. If the improper lubricant is used, temperatures will increase in the seal chambers leading to the fluid vaporizing in the seal chamber or other damage-causing conditions. Using the correct lubrication is just as important as using the correct seals. The four most common lubricants are:

• Greases—These are usually mineral oil mixed with thickeners to create a sticky fluid. The stickiness creates a protective barrier that sticks to the surfaces.
• Oils—Oils are usually thin liquids with antioxidants added to stop the oil from oxidizing and corroding. It’s a common alternative if you’re trying to avoid grease.
• Penetrating lubricants—These lubricants aren’t built for long-lasting lubrication and are very specific for the intended use of infiltrating the small cracks on surfaces.
• Dry lubricants—Dry lubricants come in spray and solid form to create a slippery surface. Spray lubrications are often mixed with alcohol to evaporate after use. Solid forms, such as silicone, are more permanent.

Be Aware of Improper Installation

By fully understanding the importance of installation, technicians can help increase the life of the seals and the system. The correct installation of a seal directly impacts wear and tear during operation. If the right type and amount of lubrication is used, friction remains low. In cases in which seals are installed improperly, misaligned, or not 100% geometric, these fragile seals will fail.

Trust Repair Experts

A tested and correctly executed maintenance plan is crucial to saving time and money and ensuring scheduled operations. However, even with routine maintenance, you’re bound to encounter scenarios where your equipment will require repairs. At that point, it’s essential you reach out to an industrial pump repair or industrial gearbox repair expert who will get your equipment back in working order in no time.

About the Author

Lorain Wilson is the content marketing specialist at Houston Pump and Gear.

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