Mercer Valve Pressure Relief Valve 91-12D21TA7L4

Warning: This inspection requires trained personnel with PPE!

The set pressure inspection is performed in accordance with the ASME BPVC.

The set pressure tolerance is 3% for valves set 70 psi and above, and 2 psi for valves set below 70 psi.

The set pressure test should be performed before and after any repairs.

The set pressure is inspected to the definition listed in NB-18.

The correct fluid for testing has to be used to achieve accurate results.

Setting procedures should be in accordance with ASME PTC 25.

The rate of the system pressure increase should be slow when the pressure is within 15% of the set pressure.

The procedures for testing set pressure are as follows.

Warning: Only trained personnel should perform this procedure

Valve removed from the application

Thorough inspection of the valve performed

Is the valve transport necessary?

Select the type of mobile test unit used

Note: The limitations of the test stand should be documented and the test stand should only be used for the sizes and pressure that it is designed for

Document the limitations of the test stand

Enter the pressure the valve is designed for

Warning: Ensure the valve is not pressurized before starting the inspection

Cap and Seal Wire in good condition

Flanged Connections show no signs of wear or improper fastening

Threaded Connections are undamaged

Outlet is free from corrosion or debris accumulation

External Surface and attachments are undamaged

Valve Tag information corresponds to the service conditions

If any of the above checks fail, the valve is deemed dangerous to test and should be replaced or repaired immediately

Sign off on the visual inspection

Warning: This procedure requires trained personnel!

Two pressure gauges used for testing?

Gauges reading identical values within their respective tolerances?

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

At least one analog (dial) gauge used?

Digital gauge used for the second gauge?

Note: Digital gauges have to be used carefully because quick pressure increases are not always seen on the gauge readings

Test gauges have at least 0.25% accuracy over their full scale?

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

Offsite testing allows for the most thorough and accurate testing and inspection

The valves are removed from the units and brought to a shop

In the shop, a valve can be completely tested and inspected

The shop environment gives the technician the most advantages because more tools are available, there is adequate space to work, and test benches enable accurate results

All of the same concerns in testing are still present in offsite testing as in situ testing

The volume of pressure, valve simmer, pressure losses to the gauges, and supply line pressure are all factors in getting an accurate result

Proper assembly of a test bench is crucial in limiting these effects

The main disadvantage in offsite testing is time

A valve must be removed from the unit and then transported to the shop