We just discovered that one of the seals on our pumping system is leaking. Do you have any ideas as to what could have caused this, and can you offer some advice for selecting a good seal?
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The main causes of external lubricant leakage from pumping systems, hydraulic machines, gearcases and sumps are the wrong selection, improper application, poor installation and inadequate maintenance practices that are applied to sealing systems.
These problems can be overcome through a better understanding of the types of sealing materials available, redefined selection procedures and the consistent application of sound replacement and maintenance practices.
A number of variables must be considered when selecting oil seals. There are nine factors that designers and maintenance engineers must evaluate when oil seals are specified:
The maximum allowable shaft speed is a function of the shaft finish, runout, housing bore and shaft concentricity, type of fluid being sealed and the type of oil seal material.
The temperature range of the mechanism in which the seal is installed must not exceed the temperature range of the seal elastomer.
Most conventional oil seals are designed only to withstand very low-pressure applications (about 8 psi or less). If additional internal pressure is present or anticipated, pressure relief is necessary.
Longer seal life can be expected with shafts having a Rockwell (RC) hardness of 30 or more. When exposed to abrasive contamination, the hardness should be increased to RC 60.
Most effective sealing is obtained with optimum shaft surface finishes. The sealing efficiency is affected by the direction of the finish tool marks and the spiral lead. Best sealing results are obtained with polished or ground shafts with concentric (no spiral lead) finish marks. If you must use shafts with spiral finish leads, they should lead toward the fluid when the shaft rotates.
When the bore and shaft centers are misaligned, seal life will be shortened because the wear will be concentrated on one side of the sealing lip.
The best seal performance is achieved when close shaft and bore tolerances are present. Other factors include shaft eccentricity, end play and vibration.
Runout must be kept to a minimum. Movement of the center of rotation is usually caused by bearing wobble or shaft whip. When coupled with misalignment, this problem is compounded. Contrary to popular belief and common practice, the installation of flexible couplings cannot correct or compensate for misalignment.
Seals perform much better and longer when they are continuously lubricated with an oil that has the correct viscosity for the application and that is compatible with the seal lip elastomer material. The consideration of seal incompatibility, particularly with certain additives and some synthetic lubricants, should not be ignored, but unfortunately very often is.
Different Types of Oil Seals
Are you looking to keep your machinery free from any unwanted leakages but aren&#;t sure which rotary shaft seal is right for your needs? This guide will provide you with everything you need to know in order to select the right one for your application.
Oil seals, which are also known as rotary shaft seals, fluid seals or grease seals, play an important role in closing down the gaps between moving and stationary elements of mechanical equipment.
By preventing lubricants from escaping, they protect key components of machinery from being damaged by leaks of various fluids. Everything from car engines to assembly machines use these oil seals to remain free from any harmful interactions that can cause serious and expensive damage to any of their critical parts.
There are a wide range of oil seals to select from for any number of uses, so this guide will break down the most common seals to help you choose the right one for whatever piece of machinery you are working on.
What are rotary shaft seals?
Rotary shaft or oil seals are placed between moving and stationary pieces of machinery to ensure that contaminants, moisture, corrosive materials and abrasives do not damage the various components. They can also prevent unwanted mixing of fluids, including water and oil combining within a machine.
How are Oil Seals made?
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First, an elastomer, most often nitrile, is vulcanised to a metal ring. This creates a stiffening effect that includes a specialised metal tension spring directly behind the sealing lip, keeping the oil seal firmly in place against the moving part.
Oil Seal Materials
There are many different materials used to manufacture oil seals.
Leather Oil Seals - Leather Seals, also known as Type L Oil Seals, are most common in components that are subject to dirt and poor lubrication. Since they come pre-lubricated and are able to absorb fluids, leather oil seals are able to provide sealing properties in conditions that synthetic rubber is unable to.
Synthetic Rubber Oil Seals - Styrene Butadiene Rubber oil seals, or just SBR oil seals, offer strong resistance to abrasions and lesions, making them an ideal seal for fast-moving machinery. With the ability to withstand extreme temperatures with its heat-aging qualities, they can be used in outdoor components. They are also seen as more cost-effective oil seals than natural rubber.
Nitrile Oil Seals - Nitrile oil seals, which is the commonly used term for acrylonitrile-butadiene rubber seals, is a very good general-purpose option due to the flexibility of use across a variety of components. The resistance is strong against fats, hot water, gasoline, mineral oils, grease and animal oils, making them the most often-used oil seals. They do not have a wide temperature range, making them a poor choice for machinery that can see extreme changes in temperature.
Viton Oil Seals - A synthetic rubber and fluoropolymer elastomer, Viton is used to make oil seals that provide resistance in both high temperature, up to 250°C and low compression set components. They also offer a high resistance to chemicals and abrasions, so they can be used in elements that regularly interact with petroleum and solvents.
Polyacrylate Oil Seals - Mostly selected for automotive and transmission uses, polyacrylate seals are able to withstand fuel, oil, ozone, sunlight and weather when used. With cars exposed to all these different fluids and elements, they are the perfect choice. However, they should not be used in low temperatures, as their flexibility weakens when cold.
Silicone Oil Seals - Designed to absorb lubricants in order to lessen wear and friction, silicone rotary shafts also offer high thermal resistance and a large temperature range. But, they do not handle abrasions well or interact with oxidized oils.
PTFE Oil Seals - A relatively new and exciting oil seal, the use of polytetrafluoroethylene means that they can withstand dry or unlubricated operations. With a massive thermal range of -130ºC to +200ºC and a strong resistance to chemicals, they are considered to be the future of rotary shaft seals.
How to Choose the Right Oil Seal
There are several key factors to consider when you are selecting the oil seals for your next project to ensure that you protect your machinery from immediate and long-term damage.
Pressure - Many oil seals can only withstand low-pressure applications, so understanding the compression set of your components is key.
Temperature - Just like pressure, the temperature that your oil seal will be operating in must be known so that you can choose one that can withstand the heat or cold. PTFE have the widest range of temperature, making them useful for machines who can see usage in extreme weather or elements.
Shaft Speed - Considering the speed that the shaft will be moving, the runout, the housing bore and the type of oil being sealed is vital to making sure you select an oil seal that will not suffer from abrasions or spiralling.
Fluid Types - Various oil seals are able to withstand interactions with oils, fuels, grease, water and more. Knowing what type of fluid the rotary shaft seal will be in constant contact with will ensure the longevity of the seal and surrounding components.
Lubricant Amount - Seals will always perform best when lubricated, however in some machines there are more likely to be dry spells. For these cases, selecting a leather or PTFE seal will be beneficial, as both can operate with less lubrication than others.
If you require any assistance in discovering the factors that lead to the right oil seal choices, the Simply Seals Team is happy to assist you!
Find the right Oil Seal for your needs with Simply Seals!
With dozens of specifically-designed oil seals made from a variety of materials, it can be very difficult to understand the best choice for their machinery.
That is why the Totally Seals team is always available to assist you with choosing the correct style, material, and size of oil seal for everything from commercial machinery to hobby car building.
Contact us today to make sure that you select the proper rotary shaft seal that will protect your components and lead to a long, healthy life for all of your machines!
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