Mercer Valve Pressure Relief Valve 95-60A10012

During the set pressure inspection, the set pressure is verified in accordance with the ASME Boiler and Pressure Vessel Code.

For all valves set 70 psi (500 kPa) and above, the set pressure has a tolerance of ±3% of the nameplate set pressure.

For all set pressure below 70 psi (500 kPa), the tolerance is ±2 psi (±15 kPa) of the nameplate set pressure.

If the valve has a CDTP associated with it due to temperature and/ or backpressure, the test pressure is checked to the CDTP.

Even with a CDTP, the set pressure tolerance is calculated based on the actual nameplate set pressure.

The set pressure test should be performed before (if it passes the visual inspection) and after any repairs.

The set pressure is inspected to the definition listed in NB-18, a publication by the National Board of Pressure Vessel Inspectors, which is found at http://www.nationalboard.org/.

This publication lists all ASME Boiler and Pressure Vessel Code certified pressure relief valves.

It indicates the correct set pressure definition and other characteristics of a valve.

Warning: Only qualified repair personnel should perform this maintenance

Is there no pressure within the main valve or pilot valve?

Does the PRV match the application?

Are there any apparent problems with the PRV?

Is the nameplate information correct?

Is there any damage to the valve?

Are there any issues that would keep the valve from opening or inhibit flow?

After the set pressure is verified, the valve undergoes a leak inspection.

This is performed to verify the disk and seat are sealed to a degree appropriate for the type of pressure relief valve being tested.

Leak tests are always performed below the set pressure of the valve, usually at a certain percentage of the set pressure.

The leak check is usually performed at 90% of the set pressure or 5 psi (34.5 kPa) below the set pressure, whichever is greater.

If the valve has a CDTP, the leak test pressure will be below the CDTP in lieu of the set pressure.

Mercer Valve should be contacted for proper leak pressure and specification for the valve.

In the tests, the pressure is held steady for a length of time and the valve is observed for any leakage.

Before this test is performed, the valve must have had its set pressure examined.

There are several methods used in testing for leakage.

Warning: This procedure requires trained personnel!

Are two pressure gauges used for testing?

Are the gauges reading identical values within their respective tolerances?

If the gauges are not reading identical values, both should be checked for calibration.

Does the test gauge have at least 0.25% accuracy over their full scale?

Is the portion of the gauge used more stringent than the set pressure’s tolerance?

For analog gauges, is only the middle 1/3 or less of the gauge used?

Is each gauge calibrated using a dead weight tester?

Sign off on the monthly gauge calibration

- Pressure Relief Valve In Situ Testing

Testing and inspecting in place eliminates the laborious task of removing and handling the valve.

This is especially desirable with large PRVs.

Additionally, not disturbing the existing connections reduces the chance of compromising the existing seals.

This type of testing is very useful when a system cannot be shut down for long lengths of time.

There are disadvantages to this type of testing.

The inspection process is more difficult because the accessibility of the valve is reduced.

The outlet pipe is often still attached and the internal parts are not observable for the visual inspection.

This can also make it difficult to leak check.