Table of contents
Whether replacing an ISO 3601 O-ring on a flange or equipping a new system with ISO 3601-3 sealing rings during production, O-rings are important and indispensable components in many industries. A sealing ring that complies with the ISO 3601-1 O-ring standard ensures that hydraulic systems remain leak-proof over a long period of time, even under high pressure. The ISO 3601 O-ring thus guarantees the functionality of individual components, right up to complete industrial plants. We have compiled further information, such as an O-ring dimensions table, here to help you find the right ISO 3601 O-ring every time.
Introduction to the ISO 3601 O-ring standard
The first version of the international O-ring standard ISO 3601 was published back in 1978. This laid the foundation for standardized O-rings in accordance with ISO 3601 and DIN 3601. The first section of the ISO 3601 O-ring standard only contains the dimensions for O-rings, with ISO 3601 and DIN 3601 closely following the outdated DIN 3771. Since 2008, ISO 3601 has also reflected the American O-ring dimensions (AS 568). The imperial dimensions are converted into millimeters for this purpose. Section 3, or ISO 3601-3, describes the differences to AS568 and refers to the tolerance of an O-ring and the quality of its surface.
ISO 3601 divides O-rings into classes A and B. Class A is based on the current American standard AS 568B (except for the 900 series O-rings for pipe fittings). Important: The size code for these O-rings in ISO 3601-1 is identical to the AS 568 bar code. Note: ISO standard section 3601-01 covers topics relating to the inner diameter, cord thickness, dimensions, and O-ring tolerances.
Class B represents a solution for manufacturing an O-ring in accordance with ISO 3601 in a metric size that is both technically sound and cost-effective. Compared to Class A, the tolerances for Class B O-rings are greater, which means they can be used for more general purposes. The size code for this class consists of two parts. The first digit defines the cross-section group (AE), while the last four digits define the inner diameter of the O-ring, rounded to the nearest tenth of a millimeter.
The ISO 3601 O-ring standard defines the O-ring material, its fit, and the permissible tolerances of the sealing rings. The decisive factor for manufacturers and customers is that the ISO 3601 standard is internationally valid. This O-ring standard ensures that the properties of O-rings are uniform everywhere. ISO 3601-1 specifies the dimensional tolerances of O-rings so that all requirements for industrial use are met. Section 3 of ISO 3601, or ISO 3601-3, which was actually developed for general-purpose O-rings, has been expanded over time to include the three defect classes N, S, and CS.
Class N describes the acceptance standard for general-purpose O-ring variants.
- In contrast, S class O-rings must meet higher quality requirements. Since these sealing rings are used in sensitive industrial applications, as well as in aerospace, the tolerances of these O-rings must be correspondingly smaller than the tolerance of a class N O-ring.
- In class CS, too, the tolerances of an O-ring must be very small. This is because a Class CS O-ring according to ISO 3601-3 is preferably used in critical sealing applications. Thanks to the low tolerances of such an O-ring, this variant is preferably used in critical and sensitive applications, such as in the aerospace industry and in companies that work with oxygen or process it in their operations.
What is the function of an O-ring?
O-rings according to DIN 3601 or ISO 3601-3 are O-shaped seals that differ in shape from flat seals. The sealing rings, made of a deformable elastomer, consist of a closed ring with a circular cross-section. The sealing effect of an O-ring according to ISO 3601, ISO 3601-1, and ISO 3601-3 is achieved by compressing the elastomer between the two sealing surfaces. Due to the low tolerances of O-rings, O-rings in accordance with ISO 3601-1 or ISO 3601-3 can also be used in the form of rod and piston seals for hydraulic cylinders. In this application, it is also essential to have a corresponding groove in the system to be sealed, into which, for example, the ISO 3601-1 O-ring fits.
In industrial and private applications, an O-ring in accordance with ISO 3601-1 is indispensable for sealing hydraulic and pneumatic systems. O-rings reliably prevent liquid and gaseous substances from escaping. Precise manufacturing is therefore crucial for an O-ring in accordance with DIN 3601. For this reason, seals in accordance with O-ring ISO 3601 or ISO 3601-1 must meet tight O-ring tolerances. ISO 3601, which is equivalent to DIN 3601, defines in detail the dimensions, materials used, and tolerances of O-rings. This ensures that an O-ring according to ISO 3601 is reliable in operation and functions flawlessly in different environments, even under high temperatures, pressures, and in interaction with gases and liquids.
An ISO 3601 O-ring is essential in hydraulic and pneumatic pumps that operate at high pressures. Absolute tightness is a top priority here, as otherwise liquids such as oil or coolant could escape from the system. To seal flanges, pipes, or entire components against each other, an ISO 3601 O-ring is placed in the groove provided for this purpose. A low tolerance for an O-ring and the associated high dimensional accuracy are extremely important here. On the other hand, too much tolerance in an O-ring can lead to leaks and pressure loss in the system. The tolerances for an O-ring according to ISO 3601 are designed so that the sealing ring deforms under pressure and seals the respective area optimally.
Explanation of dimensions according to ISO 3601
According to the definition in DIN 3601, an O-ring is a closed ring, also referred to as a cord, which has a round cross-section. The dimensions of an ISO 3601 O-ring are defined by d1, the inner diameter, and d2, the cord diameter or cord thickness. An IS 3601 O-ring is often marked with the abbreviation CS. This parameter is expressed in inches or mm and can be calculated by subtracting twice the cord diameter (d2) from the inner diameter (d1). Depending on the application, the CS sizes, in addition to the lowest possible O-ring tolerances, are decisive for the accuracy of fit and tightness of the system. As a rule, these O-ring dimensions can be found in the manufacturer's table, but they can also be determined independently with a suitable measuring tool.
Notes: To determine the correct size of an ISO 3601 O-ring, it is essential to know the groove size at the installation site. In addition to the tolerances of an O-ring, it must also be noted that the inner diameter of the O-ring must be at least 15% smaller than the diameter of the groove. The reason for this is that the elastomer from which the O-ring is made requires space when compressed. If there is not enough space, the O-ring can be damaged. Therefore, before installation, the O-ring dimensions must first be taken from the table in order to be able to apply the expansion of the inner diameter. This is because, when installed, the diameter of an O-ring expands by up to 5% in static application and can also be compressed by up to 3%.
Advantages of using ISO 3601-compliant O-rings
In industry, the sealing technology used must comply with international standards. Whether developing a hydraulic system or repairing a forklift truck, both engineers and maintenance technicians must ensure that only approved ISO 3601 B112 O-rings are used, for example, depending on the area of application. Seals that meet this O-ring standard fit perfectly into the groove provided and are also very durable. The ISO 3601 O-ring also ensures that a standardized sealing ring always has the required dimensions. This also minimizes the risk of the O-ring being extruded or damaged under pressure and thus losing its sealing effect.
By predominantly using ISO 3601-compliant sealing rings in industry, such as those in the sizes ISO 3601 B112, companies can be sure that the seals are always consistent and meet all requirements. Thanks to the low O-ring tolerances mentioned above and a standardized material composition, the risk of leaks and operational failures is minimized. This saves maintenance costs and increases operational safety. In addition, standardization simplifies the procurement process, as compatible O-rings are available worldwide. For B2B customers, this means greater efficiency and reliability in their projects, as they can rely on compliance with the specified O-ring tolerances, sizes, and reliability.
| Use case | Flange gasket | Piston seal | Rod seal | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Method of application | Static | Static | Dynamic | Static | Dynamic | |||||
| Thickness of the O-ring | Groove width | Nut depth | Groove width | Nut depth | Groove width | Nut depth | Groove width | Nut depth | Groove width | Nut depth |
| 1 | 1,9 | 0,7 | 1,58 | 0,7 | 1,58 | 0,75 | 1,58 | 0,7 | 1,58 | 0,75 |
| 1,5 | 2,8 | 1,1 | 2,19 | 1,05 | 2,19 | 1,15 | 2,19 | 1,05 | 2,19 | 1,15 |
| 1,78 | 3,2 | 1,3 | 2,53 | 1,3 | 2,53 | 1,4 | 2,53 | 1,3 | 2,53 | 1,4 |
| 2 | 3,4 | 1,5 | 2,78 | 1,5 | 2,78 | 1,6 | 2,78 | 1,5 | 2,78 | 1,6 |
| 2,5 | 3,9 | 1,9 | 3,37 | 1,9 | 3,37 | 2 | 3,37 | 1,9 | 3,37 | 2 |
| 2,62 | 4 | 2 | 3,51 | 2 | 3,51 | 2,1 | 3,51 | 2 | 3,51 | 2,1 |
| 3 | 4,6 | 2,3 | 3,98 | 2,3 | 3,98 | 2,4 | 3,98 | 2,3 | 3,98 | 2,4 |
| 3,53 | 5,3 | 2,7 | 4,67 | 2,7 | 4,67 | 2,8 | 4,67 | 2,7 | 4,67 | 2,8 |
| 4 | 6 | 3,1 | 5,23 | 3,1 | 5,23 | 3,3 | 5,23 | 3,1 | 5,23 | 3,3 |
| 4,5 | 6,5 | 3,5 | 5,9 | 3,5 | 5,9 | 3,8 | 5,9 | 3,5 | 5,9 | 3,8 |
| 5 | 7,4 | 3,9 | 6,48 | 3,9 | 6,48 | 4,3 | 6,48 | 3,9 | 6,48 | 4,3 |
| 5,33 | 7,6 | 4,2 | 6,86 | 4,2 | 6,86 | 4,6 | 6,86 | 4,2 | 6,86 | 4,6 |
| 5,5 | 7,6 | 4,4 | 7,05 | 4,4 | 7,05 | 4,8 | 7,05 | 4,4 | 7,05 | 4,8 |
| 6 | 8 | 4,8 | 7,59 | 4,8 | 7,59 | 5,2 | 7,59 | 4,8 | 7,59 | 5,2 |
| 7 | 8,7 | 5,7 | 8,68 | 5,8 | 8,68 | 6 | 8,68 | 5,8 | 8,68 | 6 |
| 8 | 9,8 | 6,7 | 9,88 | 6,8 | 9,88 | 7 | 9,88 | 6,8 | 9,88 | 7 |
| 9 | 11,2 | 7,6 | 11,14 | 7,7 | 11,14 | 7,9 | 11,14 | 7,7 | 11,14 | 7,9 |
| 10 | 12,2 | 8,6 | 12,38 | 8,6 | 12,38 | 8,8 | 12,38 | 8,6 | 12,38 | 8,8 |
Further advantages of DIN 3601 and ISO 3601 O-rings at a glance
- An O-ring in accordance with ISO 3601 or DIN 3601 is characterised by its low space requirement and simple installation - ISO 3601 B112 O-rings enable simple sealing construction The resistant materials used in O-rings in accordance with DIN 3601 or ISO 2601 ensure that they can be used in a wide temperature range from -100 °C to over +300 °C. - The low tolerances of an ISO 3601 O-ring allow it to be used in systems that operate with high vacuum or high pressure of up to 3000 bar. - Manufacture is relatively simple, which means that an ISO 3601 or ISO 3601 B112 O-ring, for example, is inexpensive and always available
Note: Class A O-rings that comply with ISO 3601 or the quality requirements in section ISO 3601-1 also have lower tolerances than an ISO 3601 O-ring of the Class B variant. For this reason, Class A sealing rings are also used in extremely demanding environments such as the aerospace industry.
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