Positioner-embedded analytics that move beyond NE107-style status flags to predicted remaining useful life and a recommended maintenance action.
Automated partial-stroke & proof testing
Automated partial-stroke and proof-test functions for safety valves, built into positioners, smart solenoids and safety systems. The technique is decades old; what is maturing is the record-keeping that lets a test count toward the safety case.
Why safety valves need testing
A safety instrumented function protects against a hazard only if its final element, usually a shutdown valve, actually moves when demanded. Most of these valves sit open and still for years. Failures such as a stuck stem, a seized actuator or a failed solenoid are dangerous and undetected: nothing reveals them until the valve is called upon. IEC 61511, the functional-safety standard for the process industries, therefore requires periodic proof testing at an interval consistent with the target safety integrity level.
A full-stroke proof test closes the valve, which normally needs a bypass or a process shutdown. A partial-stroke test (PST) moves the valve through a small part of its travel, often around 10 percent 3, while the process keeps running, and confirms that it is free to move. It cannot prove that the valve closes fully or seals, so it supplements full proof tests rather than replacing them.
What gets automated, and how it earns safety credit
A PST can be run by a digital positioner or a smart solenoid mounted on the valve, by the safety system itself, or by a separate test device. Automated versions record a pressure-against-travel signature and a timestamp for every test. That removes two weaknesses of manual testing: tests skipped when the schedule is tight, and results that exist only on a paper sheet.
The safety credit comes from diagnostic coverage. If a partial stroke reliably reveals a defined share of the valve assembly's dangerous undetected failures, the function's average probability of failure on demand falls. That can allow a longer interval between full-stroke tests for the same safety integrity level, or let a simpler architecture meet the same target. The share depends on the valve type, actuator, service conditions and test method, which is why ISA-TR96.05.01, ISA's technical report on partial-stroke testing of automated valves 1, and the supplier's failure-mode analysis for the specific assembly both matter.
| Failure | Partial-stroke test | Full-stroke proof test |
|---|---|---|
| Valve stuck or seized | Detected | Detected |
| Slow stroke or excess friction | Usually indicated | Detected |
| Solenoid failure to vent | Detected if the test uses the solenoid | Detected |
| Failure to reach the fully closed position | Not detected | Detected |
| Seat leakage | Not detected | Detected if a leak test is included |
The limits
- A partial stroke says nothing about tight shut-off. Where seat leakage matters to the safety function, only the full test, with a leak check, proves it.
- Diagnostic-coverage figures from data sheets assume particular conditions. Applying them without checking that they fit your valve, service and test frequency overstates the credit.
- A PST can trip the process if a sticking valve breaks free and overshoots the test limit. Test design and abort logic deserve as much attention as the test itself.
- Automation does not remove the need for a competent person to review results and act on failed or degraded tests.
Where it is going
The direction of travel is toward joining test records to maintenance and safety-lifecycle software, so that evidence that each function performs as designed accumulates continuously rather than being assembled before an audit. Some operators also trend PST signatures, watching friction and stroke time to plan repairs before a valve fails a test. That convergence with general valve diagnostics is why this entry sits close to predictive valve diagnostics on the curve.
Practitioner guidance has long stressed that automated valves need a testing programme designed around their actual failure modes, not just a schedule 23. The tools to do that well now exist in mainstream products; the remaining work is in specification and discipline.
Evidence timeline
- 2016IEC 61511 second edition sets current requirements for proof testing of safety instrumented functions in the process industries.
- 2017ISA publishes ISA-TR96.05.01-2017 on partial-stroke testing of automated valves. 1
- 2020Trade-press guidance highlights gaps in how automated valves are tested in practice. 2
Why it sits at the Industry Acceptance stage
Partial-stroke testing is long established on safety valves in refining and petrochemicals, and automated test functions are standard in current positioner and smart-solenoid ranges. We place the entry at Industry Acceptance rather than Proven in Use because consistent use of the test records, in safety calculations and in maintenance planning, is still uneven across the industry and across other process sectors.
Adoption signals to watch
- Safety-lifecycle software that imports PST results automatically and updates proof-test status.
- Wider use of PST outside refining and petrochemicals, for example in pharmaceuticals, water and power.
- Supplier failure-mode data for specific valve assemblies, rather than generic coverage figures.
Questions to ask before committing
- What diagnostic coverage is claimed for the partial stroke, for which failure modes, and on what evidence for our valve assembly?
- Is the test interval in the safety calculation the one the plant will actually achieve?
- What stops a partial-stroke test from tripping the process if the valve sticks and jumps?
- Where are test results stored, who reviews them, and how quickly is a failed test acted upon?
Terms used on this page
- Partial-stroke test
- Moving a safety valve through a small part of its travel to confirm it is free to move.
- Proof test interval
- The time between tests assumed in the safety integrity calculation.
- IEC 61511
- The functional-safety standard for safety instrumented systems in the process industries.
Sources
- ISA-TR96.05.01-2017, Partial stroke testing of automated valves
- What you should know to adequately test automated valves
- Use of digital technology to test shutdown valves for SIS applications
Related technologies
See this entry on the full maturity map · All Control Devices entries · How placements are made. Stage and time-horizon placements are editorial judgements based on the public sources listed above, as of October 2026. They are not engineering, safety or investment advice; see the Terms of Use.