A canted coil spring can meet its dimensional and load requirements during inspection and still perform differently after installation in a spring-energized seal.The reason is that a spring does not work independently in this application. It sits inside a groove in a PTFE or other polymer seal jacket, where its deflection provides the force needed to support the sealing lip. The available groove space, jacket dimensions, assembly tolerances, and installed compression all affect how the spring behaves.
This is why Canted Coil Spring Testing should not stop at checking free dimensions and initial load. Those measurements are necessary, but they do not show the complete operating condition of the spring inside the seal assembly.A sound qualification process needs to cover both the spring itself and its installed condition. This article examines five testing mistakes that can lead to misleading qualification results and explains what to check when evaluating canted coil springs for spring-energized seals.
The scope of Canted Coil Spring Qualification depends on the seal design and its operating conditions. A basic inspection may be sufficient for some applications, while others require additional checks on load retention, environmental exposure, or the complete seal assembly.The following table outlines the main areas commonly considered during qualification.
| Test area | Items to check | Purpose |
| Dimensional inspection | Free height, spring width, inside diameter, outside diameter, and other specified dimensions | Confirm that the spring matches the drawing requirements |
| Load testing | Spring load at a defined compression or deflection | Check whether the spring provides the specified force under the test condition |
| Dimensional and load consistency | Differences between samples and production batches | Identify variation that may affect assembly or performance |
| Installation assessment | Fit between the spring, groove, and seal jacket | Check the spring in its intended installation space |
| Environmental testing | Temperature, exposure media, and other specified operating conditions | Assess whether the environment affects spring performance |
| Cycling and retention testing | Load or dimensional changes after a defined period or number of cycles | Evaluate performance changes during the specified test |
These checks do not all carry the same weight in every project. A static seal, for example, may have different qualification requirements from a seal exposed to repeated movement. The test scope should reflect the actual application rather than follow a fixed checklist without considering the design.
Spring load must always be evaluated in relation to its compression or deflection.A canted coil spring may produce different loads at different installed heights. If the test fixture does not reflect the actual seal installation, the measured load may not represent the spring’s performance in the finished assembly.For example, a spring may meet the load requirement between two flat test plates, but its actual deflection can change after installation due to groove depth, seal jacket dimensions, and assembly tolerances.
Before carrying out Canted Coil Spring Load Testing, confirm:
The test report should include the compression height or deflection for each load measurement. Without this information, test results are difficult to interpret or compare.For spring-energized seals, spring force and deflection must be considered alongside the seal design. See our spring-energized seal working principle for more information.
A spring may meet its free-dimension requirements but still be unsuitable for the intended groove.Groove width, depth, and geometry determine the space available for spring deflection. A narrow groove may restrict movement or cause interference, while an incorrect groove depth or excessive clearance can affect the installed compression and spring position.When reviewing the design, check the following:
Nominal dimensions alone are not enough. Tolerances can change the actual installation space and affect how the spring sits in the groove.For projects still at the design stage, see our common mistakes in canted coil spring groove design to identify potential fit and installation issues early.
An initial load measurement shows the spring’s performance at the time of testing, but it does not confirm whether the spring can maintain the required load during service.A canted coil spring may remain compressed for long periods or undergo repeated compression and release. Temperature and other environmental conditions can also affect its performance, depending on the material, design, and application.Where load retention is a concern, testing may include:
Test duration, cycle count, and acceptable variation should be defined according to the product requirements and operating conditions. Not every canted coil spring requires the same retention test.High-temperature applications and springs under continuous compression deserve particular attention. Material selection also plays a role. See our spring energizer material selection guide for more information on suitable material options.
A spring may pass dimensional and load inspection on its own, but this does not guarantee that the complete seal assembly will meet its performance requirements.In spring-energized seals, the canted coil spring sits inside the polymer jacket, where its force supports the sealing lip. Actual performance depends on how the spring, groove, and jacket fit and work together.For example, the spring may meet its specified load in a standalone fixture, while the installed compression differs from the test condition. Groove restrictions or jacket dimensions may also affect spring movement and installation space.For this reason, qualification should cover two levels of testing.Individual spring testing.This stage checks the spring itself:
Complete seal assembly testing:
The spring is installed in the intended seal jacket and groove configuration, allowing the assembled seal to be evaluated under application-specific conditions.If the seal operates under pressure, temperature changes, process media, or dynamic movement, the corresponding performance checks should be included.Individual testing confirms that the spring meets its component requirements, while assembly testing verifies that the spring and seal design work together as intended.
Test results can be difficult to compare when measurement conditions are inconsistent.For example, two parties may test the same spring using different compression heights, fixtures, or loading procedures. Even if both tests are performed correctly, the resulting load values may not be directly comparable.This can cause disagreements during sample approval, supplier qualification, or production inspection, particularly when acceptance criteria have not been clearly defined.Before qualification begins, the test method and acceptance criteria should be agreed upon and documented. Key details include:
A useful test report should allow another engineer to understand not only the measured result, but also the conditions under which it was obtained.For Canted Coil Spring Testing, the following information provides a practical starting point. Additional records may be needed for projects with specific environmental or assembly requirements.
| Record category | Information to record |
| Product identification | Part number, material, production batch, and sample identification |
| Dimensional data | Free height, spring width, inside diameter, outside diameter, and other drawing dimensions |
| Load data | Measured load and the corresponding compression height or deflection |
| Installation details | Groove dimensions, installed height, and actual compression condition where available |
| Test environment | Temperature, exposure media, and other relevant test conditions |
| Cycling and retention | Test duration, cycle count, and changes measured before and after testing |
| Inspection and evaluation | Observations, measured results, acceptance requirements, and final assessment |
For spring-energized seal projects, it is also useful to keep the spring inspection records separate from the complete assembly test results. This makes it easier to trace whether a performance issue is related to the spring itself, the installation geometry, or the seal assembly.A report containing only a final load value is rarely sufficient for a detailed technical review. The associated test condition is part of the result.
Acceptance criteria need to be connected to the design requirements. Simply stating that a spring must pass a load test is not enough if the compression height, measurement method, and acceptable load range have not been defined.When preparing a qualification specification, the engineering team should clarify what is being evaluated and how conformity will be determined.For dimensional inspection, the drawing should identify the dimensions to be measured and their allowable tolerances. For load testing, the specified compression height or deflection must accompany the load requirement.
If load retention is part of the qualification, the exposure period or cycle condition and the acceptable change should also be stated.Assembly testing requires a separate set of criteria. The test should reflect the intended seal configuration and relevant operating conditions. A spring that meets its individual component specification should not automatically be treated as proof that the finished seal has passed its assembly qualification.The acceptance criteria may differ between projects. They should be agreed by the parties involved and based on the actual design, operating conditions, and product requirements rather than on assumed universal limits.
The test conditions for a canted coil spring used in a spring-energized seal depend on the service environment. The same qualification scope may not be appropriate for every application.
| Application | Main factors to consider |
| Hydraulic and pneumatic equipment | Operating pressure, dynamic movement, and sealing-lip support |
| High-temperature sealing | Temperature exposure, material stability, and load retention |
| Chemical and corrosive environments | Media compatibility and corrosion resistance of the selected material |
| Vacuum and semiconductor equipment | Seal configuration, material suitability, and cleanliness requirements |
For hydraulic or pneumatic applications, pressure and movement conditions may influence the assembly tests required. High-temperature service calls for attention to the selected spring material and its performance under the specified exposure conditions.In chemical environments, material compatibility should be assessed against the actual media and exposure conditions. For vacuum and semiconductor applications, the seal design and cleanliness requirements may also need to be included in the qualification specification.These are application considerations, not fixed test prescriptions. The operating temperature, pressure, media, movement, and service-life requirements should determine the final test scope.
Spring load is only one of the factors affecting sealing performance and does not directly determine the sealing effectiveness of the finished assembly. Once installed, the interaction between the spring, seal jacket, and spring groove, as well as the actual installed compression, can influence how the spring performs. The geometry of the sealing lip, contact conditions, and operating environment also affect the sealing result.
Therefore, individual spring testing should be treated as an initial verification step. The complete seal assembly must ultimately be evaluated against the requirements of the intended application.
If the installation dimensions have tolerances, testing only at the nominal compression may not reveal how the spring load varies across the actual assembly range. During engineering evaluation, the dimensional tolerances of the spring groove and spring should be considered to determine the possible minimum and maximum installed compression heights. The corresponding loads can then be checked against the design’s allowable range.
Whether all dimensional extremes need to be tested depends on the product tolerances, application risks, and project qualification requirements.
No. The test program should be determined by the actual operating conditions and potential failure modes. For example, static and dynamic sealing applications have different performance requirements. Applications involving high temperatures, corrosive media, or frequent reciprocating motion may also require additional environmental or cyclic testing.
The purpose of qualification is not to perform as many tests as possible, but to select test conditions that represent the actual application and effectively evaluate its critical performance requirements.
Selecting and qualifying a canted coil spring for a spring-energized seal involves more than checking the spring’s free dimensions and initial load. The installed space, groove geometry, seal jacket, and operating conditions all need to be considered as part of the design.Handa Spring works with application requirements such as spring dimensions, groove configuration, working compression, material selection, and service environment when reviewing canted coil spring designs for sealing applications.If you are developing a new spring-energized seal or reviewing an existing design, you can share the relevant drawings and operating requirements with our team. Visit our spring energizer applications page for further information about application support.
