Oil Seal Design & Selection

Design Selection

Standard Seal Designs

Standard seal designs, shown in the table below, are best for rough bore finishes or for materials with high coefficient of thermal expansion.

table showing 22 standard oil seal designs commonly used for a variety of applications

Table Notes:

Metal O.D. seals are most suitable for steel or cast iron housing materials.

Rubber covered O.D. seals are preferred for soft alloy or plastic housing materials. They are also suitable for steel or cast iron housing materials.

Selecting a Standard Seal Design

Comparing Lip Designs

I. “S” and “T” Lip Designs

The table below illustrates “S” and “T” lip symbols for general non-pressure applications. The “S” design is a single lip oil seal with a garter spring to provide consistent radial load against the shaft. The “T” design is a single lip oil seal with an auxiliary dust lip to provide effective light duty dust exclusion.

standard oil seal designs for general nonpressure applications

The table below shows approximate limits of the “S” and “T” oil seal lip designs.

Shaft Diameter	Nitrile Lip Maximum Continuous Shaft Speed¹	Maximum Continuous Pressure²	Maximum Total Eccentricity³
General	3,500 rpm	5 psi	.020″
.500	8,000 rpm	5 psi	.004″
1,000	7,000 rpm	5 psi	.006″
2,000	4,500 rpm	5 psi	.010″
3,000	3,800 rpm	5 psi	.013″
4,000	2,750 rpm	5 psi	.017″

¹ Higher shaft speeds are possible using high temperature materials
² Higher continuous pressures are possible for shaft speeds below 200 ft/min
³ Higher eccentricity is possible if shaft speed is reduced

II. “V” and “K” Lip Designs

The table below illustrates “V” and “K” oil seal designs. The “V” design is a single lip oil seal. The “K” design is a single lip oil seal with an auxiliary lip for light dust exclusion. These are low cost seals designed primarily for retention of grease and similar viscous fluids.

low cost oil seal designs for retention of grease and other viscous fluids

The table below shows approximate limits of the “V” and “K” oil seal lip designs.

Shaft Diameter	Maximum Shaft Speed	Maximum Continuous Pressure	Maximum Total Eccentricity¹
General	2,000 rpm	4 psi	.005″
.500	4,000 rpm	4 psi	.003″
1,000	3,000 rpm	4 psi	.005″
2,000	2,300 rpm	4 psi	.006″
3,000	1,700 rpm	4 psi	.008″
4,000	1,400 rpm	4 psi	.010″

¹ Higher eccentricity is possible if maximum shaft speed is reduced

III. “WP” Lip Designs

The table below illustrates “WP” oil seal designs. The “WP” were designed as dust wipers (or, scrapers) for reciprocating applications such as hydraulic cylinder rods.

The operating limits for the “WP” design are only slightly different from the “V” and “K” designs:

Maximum shaft motion is linear velocity of 200 ft./min. (1M/sec.)
Maximum pressure capability is 4 psi (.28Kg/cm²).
Stroke length should be limited to 78 inches (1.98 m) maximum.
Eccentricity considerations involve only shaft-to-bore misalignment. Maximum allowable is ±0.004 inch (0.1 mm).

Nonstandard Seal Designs

Nonstandard seal designs, shown in the table below, are best for special applications that cannot be satisfied by standard designs.

Material Selection

I. Lip Material Selection

The tables below provide comparisons for popular lip materials; however other elastomers – such as PTFE and Ethylene Acrylate – are available.

Base Polymer	Nitrile	Polyacrylate	Silicone	Fluoroelastomer
Material Code	A	T	S	F
Temperature Range	-50°F ~ 250°F -45°C ~ 120°C	-20°F ~ 300°F -30°C ~ 150°C	-80°F ~ 400°F -60°C ~ 200°C	-30°F ~ 400°F -35°C ~ 200°C
Oil Resistance	◎	◎	◍	◎
Acid Resistance	◍	△	△	◎
Alkali Resistance	◍	X	X	△
Water Resistance	◍	△	◍	◍
Heat Resistance	◍	◎	◎	◎
Cold Resistance	◍	△	◎	△
Wear Resistance	◎	◎	◍	◎
Ozone Resistance	◍	◎	◎	◎

Key:

◎ Very good

◍ Good for most applications

△ Fair, can be used if no other materials are available

X Not good

	Advantages:	Disadvantages:
NITRILE	Commonly referred to as Buna-N and is Copolymer of Butadiene and Acryonitrile. Low cost. Good resistance to petroleum oils, water, silicone oils, water, greases and glycol base fluids. Good abrasion resistance, cold flow and tear resistance.	Poor resistance to ozone and weather aging.
POLYACRYLATE	Polymerised acrylic acidesters. Good resistance to mineral oils, hypoid gear oils, E.P. additives, greases, aging and flex cracking. Higher temperature limit than Nitrile.	Poor cold temperature limit, dry running ability and water resistance. Low mechanical strength. Slightly higher cost than Nitrile.
SILICONE	Broad temperature range. Good ozone resistance. Resistant to compression set.	Low resistance to hydrocarbon fluids like gasoline or paraffin fluids, or steam above 50 psi. Cost higher than Polyacrylate.
FLUOROELASTOMER	Good temperature resistance. Compatible with wide range of fluids. Commonly chosen as high temperature replacement for Nitrile or Polyacrylate.	Fair resistance to water and dry running. Low temperature resistance is fair. High cost.

		Lip Material
Type of Fluid		Nitrile	Polyacrylate	Silicone	Fluoroelastomer
Engine Oil	SAE 30 Wt.	◎	◎	◎	◎
Engine Oil	SAE 10 Wt.	◎	◎	◍	◎
Gear Oil	Super Gear	◎	◎	△	◎
Gear Oil	Hypoid Gear	◍	◍	X	◎
Turbine Oil No. 2		◍	◍	◍	◎
Machine Oil No. 2		◍	◍	△	◎
Automatic Transmission Fluid		◎	◎	△	◎
Petroleum Base Lubricating Oil		◎	◎	△	◎
Gasoline		△	X	X	◎
Light Oil/Kerosene		△	X	X	◍
Cutting Oil		◎	◍	△	◎
Grease		◎	◎	◎	◎
E.P. Lubricants		◍	◎	X	◎
Water-Glycol		◎	X	◍	◍
Alcohol		◎	X	◍	△
20% Hydrochloric Acid Solution		△	△	△	◎
30% Sulfuric Acid Solution		△	△	X	◎

Key:

◎ Very good

◍ Good for most applications

△ Fair, can be used if no other materials are available

X Not good

II. Metal Case & Spring Material Selection

The tables below lists material specifications uses for the metal case and garter spring components.

Case
SAE NO.	APPLICATION
1008 ~ 1010	General
30302 ~ 30304	Special Corrosion Resistance Condition

Spring
SAE NO.	APPLICATION
1070 ~ 1080	General
30302 ~ 30304	Special Corrosion Resistance Condition

For general oil or grease applications, metal cases are typically produced from carbon steel. For special applications, such as when sealing sea water, corrosive fluids or gases, metal cases are typically produced from stainless steel.

For general applications, the garter springs are typically made of piano wire. For special applications, such as when corrosion or extreme heat resistance are required, garter springs are typically made of stainless steel.

Shaft Recommendations

Seal and shaft compatibility is dependent on four conditions:

shaft tolerance
lead chamfer
finish
hardness

Shaft Tolerance

The table below shows recommended shaft tolerances for general applications. Shaft tolerance range should be decreased for high speed or high pressure applications.

Diameter Inch	Tolerance	Diameter Metric	Tolerance
Up to 4.000″	±.003	Up to 100 mm	±0.08
4.001″ to 6.000″	±.004	100.10 to 150.00	±0.10
6.001″ to 10.000″	±.005	150.10 to 250.00	±0.13

Shaft Chamfer

Shaft chamfer assists in the installation process. Without a proper chamfer, the seal lip may be damaged or distorted, resulting in a dislodged garter spring. The table below shows recommended shaft chamfer.

Shaft Finish

The shaft surface roughness greatly influences the amount of lip wear. Recommended roughness is:

Rotating 10 to 20 µ inch AA (.25µM to .50 µM AA)

Reciprocating 5 to 10 µ inch AA (.13µM to .25 µM AA)

Shaft Hardness

Shaft hardness prevents excessive wear, deformation, scratches and nicks. It also allows for easy machining for proper roughness. Under normal conditions, the seal contact area of the shaft should be Rockwell C45 minimum.

Housing Recommendations

Steel and cast iron provide good surfaces for both rubber covered and metal O.D. seals.
For soft alloy bores, rubber covered O.S. seals provide better sealing capability. Metal O.D. seals occasionally back out of the bore due to thermal expansion of the soft alloy.
If plastic is used, rubber O.D. seals are recommended.

Bore Chamfer

A bore chamfer assists in the installation of the seal. Below is the recommended configuration for the chamfer. Proper chamfer angle and depth minimizes cocking or lack of squareness of the seal to the shaft and distortion of the seal case. It also reduces assembly force.

Surface Roughness

Extremely rough bore finishes may allow paths for fluid to leak between seal O.D. and bore. The table below shows recommended maximum housing bore roughness.

	Metal O.D.	Rubber O.D.
Maximum Roughness	100µ inch AA	2.50µM AA
Maximum Roughness	150µ inch AA	3.75µM AA

Bore Diameter Tolerance

The tables below shows recommended housing bore diameter, bore tolerance and nominal pressfit.

Inch Sizes

Bore Diameter	Bore Tolerance	Nominal Pressfit		O.D. Tolerance¹		Out of Round²
Bore Diameter	Bore Tolerance	Seals with Metal O.D.	Seals with Rubber O.D.	Seals with Metal O.D.	Seals with Rubber O.D.	Seals with Metal O.D.	Seals with Rubber O.D.
Up to 1.000	±.001	.004	.006	±.002	±.003	.005	.010
1.001 – 2.000	±.001	.004	.006	±.002	±.003	.006	.012
2.001 – 3.000	±.001	.004	.006	±.002	±.003	.006	.014
3.001 – 4.000	±.0015	.005	.008	±.002	±.004	.007	.018
4.001 – 6.000	±.0015	.005	.010	+.003 -.002	±.004	.009	.023
6.001 – 8.000	±.002	.006		+.003 -.002		.012
8.001 – 9.000	±.002	.007		+.004 -.002		.015
9.001 – 10.000	±.002	.008		+.003 -.002		.015

¹ The Seal O.D. is the average of a minimum three measurements to be taken at equally spaced positions.
² The Out of Round is the maximum variance between any of the readings used in determining Seal O.D.

Equivalent Metric Sizes

Bore Diameter	Bore Tolerance	Nominal Pressfit		O.D. Tolerance¹		Out of Round²
Bore Diameter	Bore Tolerance	Seals with Metal O.D.	Seals with Rubber O.D.	Seals with Metal O.D.	Seals with Rubber O.D.	Seals with Metal O.D.	Seals with Rubber O.D.
Up to 25.00	±0.025	0.10	0.15	±0.05	±0.08	0.13	0.25
25.01 – 50.00	±0.025	0.10	0.15	±0.05	±0.08	0.15	0.30
50.01 – 75.00	±0.025	0.10	0.15	±0.05	±0.08	0.15	0.36
75.01 – 100.00	±0.038	0.13	0.20	±0.05	±0.10	0.18	0.46
100.01 – 150.00	±0.038	0.13	0.25	+0.08 -0.05	±0.10	0.23	0.58
150.01 – 200.00	±0.051	0.15		+0.08 -0.05		0.30
200.01 – 225.00	±0.051	0.18		+0.10 -0.05		0.38
225.01 – 250.00	±0.051	0.20		+0.10 -0.05		0.38

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