O Rings, Gaskets and Seals
We pride ourselves on providing prompt responses and efficient lead times. Our team of engineers in California handles order planning and quality control to ensure the best possible outcomes for your orders.
An O-ring, resembling a doughnut-shaped torus, is commonly crafted from elastomers like natural or synthetic rubber, serving as a sealing device. When installed, the O-ring’s opposite sides are compressed between the walls of the cavity or “gland,” creating a zero clearance within the gland that ensures an effective seal. This seal effectively prevents the flow of liquids or gases through the gland’s internal passage.
O-rings are widely used seals in manufacturing due to their simplicity and effectiveness. They offer excellent sealing capabilities while being cost-effective and easy to install. O-ring seals are typically categorized into two main groups: static seals, where little or no relative motion occurs between mating surfaces, and dynamic seals, which function between surfaces with definite relative motion, like the seal on a hydraulic cylinder’s piston. Dynamic sealing is more challenging and requires careful design and material selection. Reciprocal motion, commonly found in hydraulic cylinders and actuators, is the most frequent type of dynamic motion that utilizes an O-ring sealing system.
O-ring selection involves considering various factors such as chemical compatibility, application temperature, sealing pressure, lubrication needs, quality, quantity, and cost. With a wide array of materials available and numerous sizes and specifications specific to certain uses (aerospace, military, etc.), there are countless possible combinations. Large manufacturers and distributors may stock as many as 14,000 individual SKUs and tens of millions of units.
From a buyer’s perspective, the basic selection process starts with the following considerations:
- Size (inch or metric)
- Temperature of the product being sealed
- Application or equipment type (dynamic or static seal)
- Material being sealed (chemical compatibility, e.g., solvent, acid, caustic, abrasive, etc.)
- Operating pressure
- Speed (if dynamic) of moving surfaces
Considering these factors helps in finding an O-ring that meets specific requirements. Additional considerations include compliance with established use standards and specifications, such as those set by the military, drinking water, food processing, aerospace, pharmaceutical industries, and more.
Essential Classification: O-ring selection is predominantly influenced by the material it is made from and certain processing methods to modify its properties. The key classification factors are:
1. Size: Determined by the interior (hole) diameter and cross-section. In the USA, inch sizes are standardized according to the AS568 (Aerospace Standard 568) specification by the Society of Automotive Engineers.
2. O-Ring Material and Classification:
O-rings are manufactured using various materials, each offering specific properties and characteristics. The commonly used materials are as follows:
- Nitrile / NBR (Buna-N): Widely used due to its excellent resistance to petroleum products and operating temperature range (-40°F to +257°F). Ideal for aerospace, automotive, propane, and natural gas applications. Special Hydrogenated Nitrile (HNBR) compounds offer improved resistance to direct ozone, sunlight, and weather exposure, with a higher temperature range up to +300°F.
- Ethylene-Propylene / EPDM: Used extensively for outdoor, weather-resistant applications and water appliances. EPDM exhibits outstanding resistance to heat, water, steam, alkali, mild acidic and oxygenated solvents, ozone, and sunlight (-40ºF to +275ºF). Not recommended for use with gasoline, petroleum oil, grease, and hydrocarbon environments. Often the first choice for low torque drive belt applications.
- Silicone / VMQ: Predominantly used in high hydraulic pressure applications and situations with highly stressed parts subject to wear. Suitable for food and medical applications due to cleanliness and lack of odor or taste. Special Phenyl silicones can be used at extremely low temperatures down to -148°F.
- Cast Polyurethane: Primarily used in high hydraulic pressure applications and situations with highly stressed parts subject to wear. Superior as static seals in extreme temperature conditions. Standard compounds handle operating temperatures ranging from -85º to +400ºF.
- Neoprene® / CR: Reasonably priced with good resistance to petroleum oils, ozone, sunlight, and oxygen aging. Preferred sealing material for the refrigeration industry due to its resistance to ammonia and Freon®.
- Fluorocarbon / FKM (Viton®): Preferred for aircraft engines, automotive fuel handling systems, and hard vacuum applications. Exhibits exceptional resistance to chemicals, oils, temperature extremes (-13°F to +446°F), low compression set, low gas permeability, and excellent aging characteristics. Not recommended for exposure to ketones, alkalis, and Skydrol® fluids.
- Fluorosilicone /FVMQ: Combines the stability of silicones with the fuel, oil, and solvent resistance of fluorocarbons. Unparalleled for aerospace fuel systems, auto fuel emission control systems, government, military, and commercial specifications. Not suitable for dynamic applications due to relatively low tear strength, high friction, and limited abrasion resistance. Also not recommended for exposure to brake fluids, hydrazine, or ketones.
Each of the above materials belongs to a “family” with characteristics adjustable through variations in chemical composition and manufacturing processes. Hardness, measured by “durometer” rating, is a key characteristic that can be adjusted. Various hardness scales are used, with the “Shore A” scale being the most widely used.
Standards and Specifications:
Certain applications require O-rings to comply with specific industry standards or regulations, such as military, aerospace, automotive, petroleum, and food processing industries. Widely used specs include AMS, AS, ASTM, MIL, NAS, NATO, AN, AS, among others.
Size Specifications:
Various established specifications exist for O-ring sizes, such as AS568, BS 1806, ISO 3601, BS 4518, SMS 1586, DIN 3771, NF T 47-501, JIS B 2401, and ISO 6149, which specify dimensions and sizes for different applications.