O-Ring, Gasket, & Seal Design

Question 1

What is an incompressible fluid?

Answer 1

a fluid that does not change the volume of the fluid due to external pressure

Question 2

What are some reasons for seal failure? (1-6)

Answer 2

• Compression Set
• Incompatibility with media
• Use of seal material outside of temperature capability
• Excessive heating due to over-compression of a dynamic seal
• Mechanical damage from over-fill
• Explosive Decompression

Question 3

What are some reasons for seal failure? (7-12)

Answer 3

• Abrasion due to lack of lubrication, debris, over-compression, excessive sliding speed, or rough finish
• Extrusion from excessive clearance, excessively soft seal material, or swelling exceeding gland volume
• Lack of compliance due to low temperature or excessively hard seal material
• Damaged surfaces of seal or gland, often from improper seal removal or parts handling
• Assembly damage from pinching or cutting seals
• Lack of confinement

Question 4

Where can I find bolting preload recommendations?

Answer 4

ASME Section VIII, Div 1, Appendix 2

Question 5

What type of seals provide greated sealing forces as the pressure increases?

Answer 5

Pressure Energized Seals

Question 6

What is O-Ring Squeeze?

Answer 6

percentage that represents the measurement of the deformation of a seal when it comes into contact with mating hardware. (100*(O-Ring cross sectional diameter - gland depth)/O-Ring cross sectional diameter)

Question 7

What is O-Ring Gland Fill?

Answer 7

The percentage of gland volume that on O-Ring cross-section displaces.

Question 8

What is the optimal range for O-Ring Gland fill?

Answer 8

60% to 85%

Question 9

What is Extrusion?

Answer 9

The distortion or flow, under pressure, of portion of seal into clearance between mating parts. Harder seal materials are more resistant to extrusion but have reduced sealing ability.

Question 10

Is an over-polished surface a good surface for gaskets and seals?

Answer 10

No, an over-polished surface finish does not retain lubrication for proper wear and tends to reduce flatness or cylindricity of surface

Question 11

What are 7 seal material selection considerations?

Answer 11

• compatibility with media
• operating temperature range
• self lubrication properties (for dynamic seals)
• hardness and strength
• resilience (memory)
• permeability
• cost