Maintenance & Reliability worked example

Preventive Maintenance Interval with historical hours between service-triggering failures of 8,000 hr: a worked example

What does the result look like when historical hours between service-triggering failures reaches 8,000 hr? The full calculation is worked below with real intermediate numbers. Use it when setting inspection or replacement frequency for failure-prone components without overmaintaining them.

The inputs for this scenario

  • Historical hours between service-triggering failures: 8,000 hr (raised for this scenario; the documented default is 3,200)
  • Average run hours per day: 20 hr / day (unchanged)
  • PM safety multiplier: 1.25 x (unchanged)

Working through the calculation

  • Applying the documented formula (Historical interval in days = historical hours between service-triggering failures รท average run hours per day) to the inputs above produces each figure below.
  • At this operating point the engine returns 320 days for recommended pm interval, the number this scenario is built around.
  • At this operating point the engine returns 400 days for historical interval in days.
  • At this operating point the engine returns 8,000 hr for historical hours between failures.
  • At this operating point the engine returns 20 hr / day for average run hours per day.

How this compares with the baseline

  • Against the tool's baseline example, where historical hours between service-triggering failures sits at 3,200 hr and the headline result is 128 days, this scenario comes in 150% above the baseline at 320 days.
  • A figure at this level is achievable when historical hours between service-triggering failures is genuinely sustained, not just peaked for a shift. It assumes failures are time- or run-hour-driven and roughly consistent; for assets that fail on cycles, load, or random infant-mortality patterns, calendar-based intervals mislead and condition-based monitoring is the better tool.

Results at a glance

  • Recommended PM Interval: 320 days (headline result)
  • Historical Interval in Days: 400 days
  • Historical Hours Between Failures: 8,000 hr
  • Average Run Hours per Day: 20 hr / day

Run it with your numbers

  • Every input above is editable in the live Preventive Maintenance Interval calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.