Rubber Seals and Gaskets

What Rubber Seals and Gaskets Are and Why They Matter

Rubber seals and gaskets form a group of parts whose main function is to prevent leakage of liquid or gas through gaps in detachable and moving joints. A gasket is installed in a static joint and seals it by compression between flanges or flat surfaces. A seal, or lip seal, operates in a moving joint and must maintain tightness during reciprocating or rotary motion of a shaft or rod.

For procurement teams, this category differs from other rubber technical goods in that failure of a single part leads to failure of an entire assembly: leakage of working fluid, loss of pressure in a hydraulic system, ingress of moisture and dust into a bearing unit. Therefore, when purchasing, it is not enough to specify the size and type of article; the material must be confirmed and matched to the working environment.

The range includes O-rings, reinforced and non-reinforced lip seals, flat and profile gaskets, sealing cords and molded profiles. Each type has its own regulatory documents and design features that determine its field of application.

Classification and Procurement Data

• O-rings of circular cross-section: GOST 9833-73 establishes design and dimensions for hydraulic and pneumatic devices, GOST 18829-73 covers technical specifications.
• Seals for hydraulic devices: GOST 14896-84, non-reinforced sealing elements for reciprocating motion.
• Seals for pneumatic devices: GOST 6678-72, differing in design and profile for air media.
• Reinforced shaft seals: GOST 8752-79, with a metal case and spring for rotating shafts.
• Flat gaskets: GOST 15180-86 for sealing flange joints, as well as cut parts from rubber sheets per GOST 7338-90 of MBS and TMKShch grades.
• Sealing cords and profiles: produced under manufacturer technical specifications, used for sealing windows, doors, panels and instrument boards.
• HS code: determined within heading 4016 for other articles of vulcanized rubber; the specific classification is agreed with the customs broker.

The specification states the article type, size, rubber group, working pressure, temperature and contact medium. Without this data, material selection remains formal and the risk of field failure increases.

Materials and Their Role in Sealing Performance

Tightness is provided not only by profile geometry but by the ability of the elastomer to retain elasticity and recover shape after load removal. Under prolonged compression, the material undergoes stress relaxation and compression set, so the choice of rubber is determined by service conditions.

• Nitrile butadiene rubber (NBR): the base material for oil- and gasoline-resistant seals in hydraulics and fuel systems. Typical range is from minus 30 to plus 100 degrees Celsius. Limited resistance to hot water and steam due to hydrolysis.
• Hydrogenated nitrile butadiene rubber (HNBR): retains NBR oil resistance with heat resistance up to 150 degrees Celsius and high ozone resistance. Used in demanding engine and oilfield seals.
• Ethylene propylene diene rubber (EPDM): used for cooling system seals, steam and water circuits and outdoor profiles. Resistant to ozone, UV radiation and hot water but has limited resistance to non-polar oils.
• Chloroprene rubber (CR): combines oil resistance with weather and ozone resistance, used in seals operating outdoors and in contact with fuels.
• Silicone rubber (VMQ): retains elasticity from minus 60 to plus 200 degrees Celsius, used in food and medical systems and in seals where mineral oils are not permitted.
• Fluoroelastomer (FKM): provides resistance to aggressive media and temperatures up to 200-250 degrees Celsius, used in the chemical and oil and gas industries.

For sealing articles, the key rubber parameters are Shore hardness, compression set resistance and resistance to swelling in the working medium. These parameters are standardized in the standard or technical specification for the specific article.

Mechanism of Sealing and Functional Role

A gasket seals a joint through initial compression created by tightening the fasteners. The material fills the micro-irregularities of the flange surface and blocks the leakage path. The lower the hardness and the higher the deformation ability, the better the filling of irregularities, but a material that is too soft is extruded from the joint at high pressure. Therefore, gaskets with a fabric reinforcement or compression limiters are used for high-pressure flange joints.

A lip seal operates differently: its edge is pressed against the shaft by the working medium pressure and by its own elasticity, while a thin fluid film between the edge and the shaft provides lubrication and sealing at the same time. Reliable operation requires the elastomer to retain elasticity at working temperature and not to swell in the contact medium. O-rings installed in a groove seal through cross-section deformation under medium pressure, and the medium pressure additionally presses the ring against the groove wall.

Applications by Industry

Oil and Gas and Chemical Industry

Gaskets for pipeline flange joints, pump seals, valves and reactors. Materials based on FKM, HNBR, CR and NBR are used depending on medium aggressiveness and temperature.

Mechanical Engineering and Hydraulics

O-rings and seals for hydraulic cylinders, rod and shaft seals, gaskets for housing parts. NBR and polyurethane elastomers dominate here, while FKM and HNBR are used for high temperatures.

Automotive and Transport

Seals for engines, gearboxes, fuel and brake systems, gaskets for sumps and covers. Resistance to oils, fuels and antifreezes over a wide temperature range is required.

Construction and Utility Systems

Flange gaskets for heating and water supply systems, profile seals for windows and doors, sealing cords. EPDM is preferred for water and steam circuits.

Food and Medical Industry

Seals and gaskets made of silicone rubbers and rubbers approved for contact with food products. Requirements for material purity and absence of migration are higher here than in technical applications.

Comparison of Materials and Typical Selection Errors

The most common error is replacing a seal by size without regard to material. An NBR O-ring installed in a hot water circuit degrades faster than an identical EPDM ring, although they are geometrically the same. The opposite error is using EPDM in contact with mineral oil, where it swells and loses strength.

The second error concerns hardness. Rubber that is too soft fills irregularities well but is extruded into the gap at high pressure. Rubber that is too hard does not compensate for flange geometry deviations and requires higher tightening. Each joint type has a recommended hardness range specified in the normative document.

The third error is reusing seals after disassembly. After load removal, the material does not fully recover its original geometry, and wear forms on the seal edge. Reinstallation of such parts does not provide tightness.

Supplier Selection Criteria and Specification Development

The specification must include the article type, size, rubber group, hardness, working pressure, temperature and contact medium, as well as a reference to the standard or technical specification. For critical assemblies, requirements for compression set and swelling resistance are additionally specified.

The supplier confirms batch-to-batch consistency of dimensions and material, the availability of a certificate of quality and the possibility of providing samples for testing. For imported articles, it is important to verify that the actual material matches the declared one, since replacing the elastomer with a cheaper analogue is not always visually noticeable but significantly reduces service life.

Typical Storage and Installation Errors

• Storage under light and heat exposure. UV radiation and elevated temperature accelerate rubber aging and reduce elasticity.
• Storage near ozone sources. Welding equipment and electric motors generate ozone that attacks unprotected rubbers.
• Deformation during storage. O-rings and lip seals must not be stored suspended or under load causing permanent deformation.
• Contamination during installation. Sand, chips and remnants of the old gasket on the flange surface disrupt sealing.
• Excessive or insufficient tightening. The former extrudes the gasket and deforms the flange, the latter does not provide initial compression.
• Absence of lubrication during seal installation. Dry installation damages the edge and causes early failure.

Quality Control at Incoming Inspection

Incoming inspection includes verification of geometric dimensions, Shore hardness, absence of surface defects and material conformity. For critical articles, tightness testing on a bench and accelerated resistance testing to the working medium are performed. If the elastomer type is in doubt, laboratory identification is carried out, for example by infrared spectroscopy or thermal analysis.

Storage and Transportation Conditions

Seals and gaskets are not classified as hazardous goods. Storage is carried out in closed dry premises at temperatures from minus 5 to plus 25 degrees Celsius, protected from direct sunlight, ozone and heat sources. Articles must be protected from deformation and mechanical damage and packed in polyethylene film or paper. Transportation is by rail, road and sea in packaging that protects against contamination and moisture.

Finding Analogues and Interchangeability

When replacing a seal, an article with similar dimensions, hardness and a material resistant to the working medium is selected. Material substitution is permissible only after confirming resistance to the contact medium and maintaining the required compression set. For imported articles, an analogue is selected per ISO 3601 or ASTM D2000 with recalculation of dimensions and tolerances. The decision is based on laboratory testing and, for critical assemblies, bench or field verification.

Supply Routes: Russia, China and Other Regions

Domestic supply is provided by rubber technical goods manufacturers and specialized molded article production facilities. Products are supplied to the domestic market and for export.

Chinese producers offer a wide range of standard and custom seals, including silicone and fluoroelastomer articles. Supplies are delivered by sea with subsequent transfer to rail or road transport. Other global producers are located in India, Turkey, Malaysia and Europe. Suppliers from these regions are engaged when required, taking into account logistical and regulatory factors.

Logistics and Customs Clearance

Transportation is carried out in packaging that protects articles from deformation and contamination. Customs clearance includes HS code classification within heading 4016, preparation of a safety data sheet if required and conformity declaration. The portal provides customs broker services and supports all clearance stages.

FAQ: Common Questions from Procurement and Process Specialists

Which material should be selected for a gasket in a heating system

EPDM, resistant to hot water and steam, is typically used for water and steam circuits of heating systems. NBR undergoes hydrolysis in these conditions and loses elasticity faster.

How does an O-ring per GOST 9833-73 differ from a lip seal per GOST 14896-84

An O-ring is installed in a groove and seals through deformation under medium pressure. A lip seal has a profile with a working edge and is intended for moving joints where compensation of shaft or rod wear is required.

Can a fluoroelastomer seal be replaced with a nitrile one

Only if the working temperature and medium permit it. FKM withstands temperatures up to 200-250 degrees Celsius and aggressive media in which NBR degrades quickly. For critical assemblies, such substitution requires confirmation by testing.

How can it be verified that a seal matches the declared material

Visual inspection does not give a reliable result. Elastomer identification uses laboratory methods including infrared spectroscopy and thermal analysis, as well as resistance testing in a reference medium.

What documents are required for seal import

Import requires a contract, invoice, packing list, manufacturer certificate of quality, transport documents and a declaration of conformity if required. The portal organizes the preparation of the document set and interaction with the customs broker.

Conclusion

Rubber seals and gaskets remain critical parts on which the tightness and performance of equipment depend. Article selection is determined not only by size but by elastomer type, hardness and resistance to the working medium. For procurement teams, the practical task reduces to correct specification development, confirmation of batch material and organization of supplies with storage conditions that exclude rubber aging.

Contact Us

For procurement inquiries and supply chain organization, contact the portal team at info@apptrade.ru.