How Many Cycles Should a Door Spring Survive?

"Make it last" is not a specification. Every door hardware spring program eventually needs one number — the cycle count the part must survive — and that number drives material, stress level, surface treatment, and price more than any other line on the drawing. Here is how to arrive at it, and what to do with it afterwards.

Start from traffic, not from a standard

Product standards give you the certification threshold. Real service life comes from traffic, and it is worth calculating both, because they often disagree.

The arithmetic is simple: openings per day × days per year × required service years. What people get wrong is the openings-per-day estimate, which varies enormously by door:

These are planning assumptions for sizing a design margin, not requirements from any standard — use them to sanity-check the number your certification target gives you, not to replace it.

Then check it against the standard your product is certified to

Door closing devices and hinges are covered by durability-graded product standards — the European EN series (EN 1154 for controlled door closing devices, EN 1935 for single-axis hinges) and the ANSI/BHMA A156 series in North America each define graded cycle counts that a complete assembly must pass. Two cautions that matter more than the numbers themselves:

• The number applies to the assembly, not the spring. Certification tests a closer or a hinge, not a bare spring. A spring that survives the assembly test in a rig may still be the first thing to relax in the field, because rigs run at controlled temperature and a real door does not.
• Editions change and grades differ by market. Work from the current edition of the standard your product is actually certified to, and tell us that number. We design to the requirement in your specification — we do not assume one on your behalf, and we would rather ask than guess.

The practical rule we use: design margin above the certification number, sized by the traffic calculation. If the standard asks for a number your traffic estimate exceeds within the warranty period, the standard is your floor, not your target.

What a real fatigue test looks like

• Both stroke endpoints are fixed, not just the peak. Fatigue is driven by stress range, so a test cycles between two defined heights or angles — the installed position and the fully-open position — because those are what the part actually sees (see our fatigue life guide).
• Frequency is limited on purpose. Running the rig fast to finish sooner introduces two artefacts: heating, which makes relaxation worse than reality, and resonance if the test rate approaches the spring's natural frequency, which makes fracture worse than reality (see our surge and natural frequency guide). A test that runs too fast is not conservative — it is invalid in both directions.
• Force is measured before and after, not just "did it break". For door springs, relaxation is the more common failure, and a part that finishes the test unbroken but 15% weaker has failed the product even though it passed the rig (see our load testing guide).
• Sample size is stated. Fatigue results scatter widely. A single sample tells you almost nothing; a small population run to failure tells you where the distribution sits.

How to read the report you get back

A fatigue report that is worth anything states all of the following. If any are missing, ask before accepting the result:

• Sample size, and which production lot the samples came from
• Both stroke endpoints, in the same units as your drawing
• Test frequency and ambient temperature
• Force at a defined height, measured before and after the run
• The acceptance criterion used — permitted force loss, and whether any fracture is allowed
• Whether failures were fractures or relaxation, and where fractures initiated

See our first article inspection report guide for how this fits alongside dimensional and material documentation.

The cost comparison nobody runs until it is too late

Front-loaded verification is a fixed, known, modest cost: samples, rig time, and a few weeks of calendar. A field failure is none of those things. For door hardware the replacement cost is dominated by labour and access — a technician, a site visit, sometimes a certified installer for a fire door — with the spring itself as the smallest line on the invoice. Multiply that by an installed population and compare it to a test that would have caught the problem before tooling. See our warranty and liability guide for how this risk gets allocated contractually, and our true cost of cheap springs article for the same arithmetic in general form.

The countermeasures that move fatigue life most are cheap when specified upfront and impossible to retrofit: shot peening, presetting, a lower working stress, and verified wire cleanliness (mill verification).

Tell us your cycle requirement and both stroke endpoints through our RFQ form and we will tell you what the design needs before tooling — see our door closer springs article for the failure modes behind these numbers, and the architectural hardware overview for the wider category.