Partial stroke test Partial stroke testing

Partial stroke testing is an important safety measure that ensures an Emergency Shut Down valve or High Integrity Pressure Protection System valve will operate as planned when needed. The Netherlocks FAITH (Fail Action Integrity Test Handling) partial stroke test device allows for partial stroke testing of valves without any risk of overshoot or process interruption. The device is fitted between valve and actuator. During testing, steel blocking pins make sure that the valve can only turn to the preset test angle (i.e. 20 degrees). This also allows for maintenance during production. The system is available both for linear as well as rotating actuators.

Ready for SIL 3

An FMEDA done by Exida shows that the PFD AVG value of FAITH comfortably falls within the defined safety ranges. Therefore, the FAITH partial stroke testing device is perfectly suited for SIL3 applications.

No risk of overshoot

The risk of actual shutdown due to trip or overshooting is excluded, as the FAITH partial stroke test device physically prevents the valve from moving past the specified test point.

Ideal for maintenance purposes

The FAITH partial stroke test device suits itself very well for maintenance purposes. Critical components can be replaced at any time without interrupting the process when the actuator is in its blocked position. Without using FAITH, control system components could only be replaced during plant stops. This is when the actuator is in its fail position.

Netherlocks FAITH partial stroke test device

Double pins centralize forces during blocking of the drive bush, which avoids damage
to the valve and actuator seals during the test

Ex (Atex) Certification

The Netherlocks FAITH partial stroke test device is Ex (ATEX) certified. For this reason, it can be used in every process environment that has the highest safety standards.

Testing ESD and HIPPS valves without interrupting process flow

The Netherlocks FAITH allows for testing valves without interrupting the process flow. Valve tests can be executed out more conveniently and more often. This ensures proper operation. It also reduces the deterioration of the valve and follows recommendations by international standards such as IEC61508 & IEC61511. These standards highly recommend all ESD and HIPPS valves to be tested on a regular basis.

Main characteristics

The Netherlocks FAITH does not make use of complicated software. Also, there is no fragile wiring and no process interruption due to testing. As the valve is 100% mechanically blocked, there is no overshoot of valves. The partial stroke test takes place in a live plant setting and is guaranteed to be safe. The production process is not interrupted due to a wrong test, a real life test is executed instead of a manipulated test at low speed. FAITH is also perfectly suited for maintenance purposes, saving valuable time. Test results are guaranteed, no test is aborted. FAITH makes use of double pin blocking above 1000 NM by standard. Furthermore, there are no additional mounting parts required between the valve and the actuator.


Faith partial stroke test device comprises a custom bracket and coupling drive bush. It is mounted between the valve and actuator and there are no additional mounting parts between valve and actuator required. The FAITH partial stroke test devices’ bracket is fitted with 2 blocking pins (standard above 1.000 NM) that enable to centralize forces, avoiding damage to the valve and actuator seals during blocking of the stem at the test angle. The FAITH’s partial stroke test device is simple in design and reliable. As it is an easy to operate tool, it will be used regularly by operators, as a standard device to execute a partial stroke test. The test can be initiated and performed both manually as well as remote from the control room.

Partial stroke test device with glass window

Spurious trip

A mechanical partial stroke testing system is the only partial stroke testing system that reduces the posibility of spurious trip to 0%. Therefore, it is regarded as a comfortable and safe test method on critical systems.

Testing procedure

The key is in the control room during normal operation. The valve can be can be opened or closed when necessary and can be operated freely. When it needs to be tested, a procedure must be followed to properly test the valve.

FMEDA test results

The FAITH System PP-Series is considered as a component of the valve-actuator combination by FMEDA. When determining the PFDavg and Safe Failure Fraction (SFF) for the final element, the failure rates of the correct version of the FAITH System PP-Series must be added to the failure rates of the valve-actuator combination.

Download brochure and data sheet of Netherlocks FAITH partial stroke test device