PROCEDURE ON – ONLINE TESTING OF SAFETY VALVE EQUIPMENT – LEGATEST’Legatest’ online valve testing
- Legatest is the process of testing pressure and safety / relief valves in situ whilst the plant remains on-line (off-line service also available).
- Typically the set pressure is determined.
- This enables the valves to be adjusted and then re-tested so they continue to operate at their correct parameters.
- Enables plant operators to test and adjust valves on-line without expensive shutdowns
- Ensures that pressure and safety relief valves are safely operating and thus plant personnel and equipment are protected.
- Reduced emissions caused by incorrectly set valves.
- Reduces energy used by eliminating the need to over pressurise the plant.
- Graphical plot is a permanent record of valve performance.
- Accurate data regarding active seat / disc diameter.
- Access to the valve spindle (either threaded or slotted).
- Valve set pressure as per the plant operator’s requirements.
Legatest – Testing Procedure
- The valve cap and easing gear are removed to allow for the fitting of the Legatest equipment.
- The draw gear of the LEGATEST, to eliminate transverse forces, is connected with the valve spindle by means of a Cardan Joint.
- A tensile force is applied in Y+ direction on the valve spindle by means of a servomotor, through planetary gear transmission (by means of the stay bar with trapezoidal thread).
- The force is increased till the spring force is overcome in y-direction and the valve responds.
- The force applied here is measured by means of a force transducer.
- The valve lift is recorded by means of a valve lift-measuring device.
- The system pressure is picked up by means of a pressure sensor at a test manometer connection.
- All three signals (system pressure, lift, force) are transmitted to a data processing unit and recorded.
- If it is found that the opening point is outside the tolerance limits of about +/- 5% of desired opening point, authorised Plant personnel will decide whether a correction of valve should be carried out by loosening the counter nut and subsequently adjusting the spring pre-stress.
- If necessary, after successful adjustment of spring pre-stress, the standard test procedure is followed again till the valve responds within the tolerance range.
- Online testing can be carried out only on those of the PSVs that have a spindle diameter more than 10 mm.