How to Measure and Identify Oil Seals

oil seal Buying Guide

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?

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.

Replacing a critical component

can be difficult to get right, especially if you do not have the original machine specifications. Thankfully, there are a few ways to identify oil seals; from their design, size and material. As there are hundreds of different oil seals available on the market, this guide will cover the four most common design types. Typically available with either a single or double lip, in Nitrile or Viton Rubber Material.

Oil Seal Single Lip vs Double Lip

Firstly, the oil seals covered in this guide classify the single lip as the inner diameter at the bottom of the component. The single lip is vital to the function of the seal by containing the oil, grease or lubricant. The only difference between a single and double lip is the additional rubber lip on the top of the oil seal which helps prevent dust or dirt from coming close to the shaft. Identifying the oil seal lip can be misinterpreted with a visual inspection alone. For or this reason, you should press along the inner diameter at the top of the seal, if you feel a ridge with a slight movement or give it is highly likely you have a double-lipped oil seal.

Industry retailers use unique codes to identify oil seals worldwide. The most common lip style designations are 21 (single lip) and 23 (double lip), please read our Oil Seal Cross Reference Guide for more detailed information.

Identify Oil Seal Design

1. Type A – Rubber Covered Lip Seals

Fully covered outer diameter for excellent sealing. This oil seal is fully enclosed in a rubber material and is the most widely used type of oil seal. Great resistance to thermal cycling, temperatures and different chemical resistance.

2. Type B – Metal Outer Diameter Oil Seals

Economic metal outer diameter for standard applications. This is an economical oil seal where the metal is exposed on one side and offers a closer fitting between the oil seal and housing or bore. Due to this, it has limited use with sealing thin liquids or gases.

3. Type C – Reinforced Metal Insert Oil Seals

The same design as type B with an additional inner case for greater structural rigidity. This type of oil seal is typically used in heavy-duty engineering machinery or large diameter sized seals

4. Type F – Stainless Steel Garter Spring

The same design as type A with corrosion protected metal case and stainless-steel garter spring. Suitable for use with a wide range of fuels and chemicals.

Identify Oil Seal Material

Nitrile or NBR is black in color, whereas, Viton or FKM is usually a brownish color. To understand the main comparisons between the two compounds read our Nitrile vs. Viton article.

Inch and Metric Oil Seal Types

Single Lip Seals

Available in a range of sizes, single lip seals are suitable for most applications.

Dual Lip Seals

Dual lip seals are typically used for difficult sealing applications requiring the separation of two fluids.

The chart below shows different design considerations for single and dual lip seals. To view our cross-reference chart, download the Oil Seals Brochure.

What is Oil Seal | Purpose , types of Oil Seal , Advantages

What is Oil Seal | Purpose , Types of Oil Seal , Advantages

OIL SEAL

Oil seals, also known as shaft seals, are radial lip type seals which are primarily used for retaining lubricants in equipment having rotating, reciprocating or oscillating shafts. The rotating shaft application is most common.

An oil seal normally consists of three basic components: the sealing element, the metal case and the spring. The purpose of the sealing element is to stop the fluid from leaking between the shaft and housing. The metal case will give rigidity and strength to the seal while it is being held in the bore or recessed groove. The garter spring ensures constant pressure and maintains the radial force to the shaft, flattening the sealing edge to a defined width. The garter spring maintains the radial force exerted by the sealing lip around the shaft surface. All materials must be selected depending on the environment in which the oil seal will function.

The performance of these seals depends to a large extent on a suitable unit load being maintained at the seal-shaft interface. These seals withstand a pressure of 15PSI and their working depends on parameters like shaft diameter, shaft speed, working temperature, service conditions, etc

Oil seals or shaft seals are an integral part in any rotating and moving part assembly. Oil seals find great deal of usage in gearboxes, hydraulic cylinders, etc. The usage of the seals in areas concerned with motion also earns them a name of “Dynamic Oil Seals.”

The purpose of the oil seals is

• To act as a physical barrier retaining the lubricating oil where it is bound to be.

• To prevent thelubricating oil from leaking outside even under high pressure of the oil.

• To act as a barrier and prevent dirt, contamination and other external entities from entering the system containing the lubricating oil.

Constructional Aspects of an Oil Seal:

1. The oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal.

2. The outer skin is made of nitrile rubber and various other materials which are used based on the requirement.

3. The spring on the lip of the oil seal tends to provide support to the lip and prevents the lubricant from leaking outside and also prevents the entry of contaminants from outside.

TYPES OF OIL SEAL

Double Lip Oil Seals

In this an auxiliary lip is provided along with the regular sealing lip. The additional dust lip protects the main sealing lip against dust and other fine solid contaminants and therefore this type is recommended for use in polluted environments. To achieve a long lifetime a suitable lubricant between the two sealing lips should be applied.

Advantages:
– Good static sealing
– Compensation of different thermal expansion
– Reduced risk of fretting corrosion
– Effective protection against air side contaminants
– Higher bore surface roughness is allowed
– Installation in split-housings
– Modern lip design provides low radial forces

Duplex Oil Seals

Sometimes, two different kinds of fluids leak from one chamber to another and gets mixed up. Here, this type comes as a boon. This is a metal inserted duplex type oil seal recommended on such assembly where mix-up of two different fluids is to be prevented.

Oil Seals without Spring

This type of oil seal can withstand only low speed and friction. It is recommended in places where thick fluid or grease is to be sealed. This is not recommended for difficult applications.

Material:

Oil seals are made out of nitrile synthetic rubber with steel stiffener rings. Other rubbers such as viton, silicon, neoprene or poly acrylic can be used for specific applications. The stiffener rings may be stainless steel or brass where highly corrosive fluids are to be sealed. Springs are generally made of spring steel to IS: 4454:Gr.ll or from stainless steel or bronze for corrosion resistance

Type A Oil Seals

Sealing of lip type seal is normally a result of an interference fit between the flexible sealing element, usually augmented by spring pressure and a shaft. Fluid retention is based on the precise amount of lip contact pressure. In most lip seals, increased fluid pressure in the sealed area causes lip contact pressure on the shaft to increase.

Advantages:
– Good static sealing
– Compensation of different thermal expansion
– Reduced risk of fretting corrosion
– Higher bore surface roughness is allowed
– Installation in split-housings
– Modern lip design provides low radial forces

Type B Oil seals

This is almost similar to that of ‘A’ type seal. But this has the metal case placed outside. When the housing is rough, temperature is high and working conditions are severe, this type is preferred.

Type C Oil seal

Type ‘C’ oil seal has an additional cup inserted into the outer cup of ‘B’ type. The supplementary metal inner ring provides a superior stiffness. This type is recommended for use in heavy polluted environments. As the static sealing between housing and metallic shell is limited, low viscosity media can “creep”.

Advantages:
– Very good fitting stability avoiding pop-out of the seal
– Modern lip design provides low radial forces
– Superior radial stiffness, especially for very large diameters
– Cost effective for expensive elastomer materials
– Suitable for use in combination with axial seal

Material used for Oil Seal :

Based on the application of the oil seal, the outer skin layer tends to differ. Here are some types of the materials used for the outer skin of the oil seal.

1. Nitrile rubber – The commonly used material for oil seals

2. Silicone – Used in specific applications where only light loads are applied.

3. Poly acrylate

4. Fluroelastomer also popularly known as Viton. – The high temperature resistant material used in places where temperature is more than 120 Degree Celcius.

5. PolytetraFluroEthylene (PTFE)

The oils seals require certain prerequisites to be maintained for their proper working. They are as follows:

a) The shaft on which the oil seal is to be mounted should be ground with the surface finish or surface roughness between 0.2 to 0.8 Microns. It is best for the shaft to be hardened atleast to 40 – 45 HRc in order to prevent groove formation on the shaft due to the pressure exerted by the spring.

b) The area where the oil seal is seated is to be plunge ground in order to prevent wear grooves that normally tend to wear out the lip of the oil seal at a faster rate.