Mercer Valve Pressure Relief Valve 81-11151V18G21

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

Cap and Seal Wire in good condition

Security seal on the seal wire intact

Flanges Connections in good condition

Threaded Connection in good condition

Outlet free from corrosion or debris

External Surface free from damage

Valve Tag information corresponds to the service conditions

If any of the checks fail, do not proceed with the set pressure inspection and the leak inspection

Warning: This inspection requires trained personnel with PPE!

Inspect the seat for cuts and abrasions

Measure the diameter Ds of the nozzle

Condition of the spherical surface

Check the portion of the disk stem that slides inside the adjustment screw bore

Inspect the set spring for damage

During the set pressure inspection, the set pressure is verified in accordance with the ASME BPVC.

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

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

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 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 BPVC certified pressure relief valves.

It indicates the correct set pressure definition and other characteristics of a valve.; The set pressure has been defined to achieve a particular operational characteristics.; If the wrong set pressure definition is used in the inspection test, the valve's set pressure will not be accurate and it may not operate appropriately.

The correct fluid for testing has to be used to achieve accurate results.; For gas/vapor service, nitrogen or compressed air is used as the test fluid, while for liquid service, water is used.; If the incorrect fluid is used during the testing, the test's results will be inaccurate.; Depending on the size of the valve and its set pressure, the set pressure discrepancy can vary outside of ASME tolerances.

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. Within this range, the rate should never be more than 2psi/sec (15kPa/sec).; Ideally each pressure increment on the pressure gauge should be clearly read as the pressure is increased. Slow pressure increase helps to accurately read the pressure gauge.

For dependable performance, PRVs must be maintained regularly.

Mercer Valve Co., Inc. recommends its PRVs are inspected and tested annually.; After the valve has been in installed and a service history has been established, the testing and inspection frequency may be adjusted.

Some guidelines for testing frequencies are found in NB-23, API 576, and API 598.; Additionally, government jurisdiction should be reviewed.; When maintenance is done, qualified repair personnel should perform it.; Qualified repair personnel conducting the annual inspection and testing may alter the maintenance schedule based on the service conditions.

During the inspection, a visual inspection, a set pressure verification, and a leak check should be completed.; These tests can be performed while the PRV is installed on its system or when it’s on a testing bench.; The PRV can only be tested while on its application if there is a method and procedure to apply a controlled pressure to the PRV’s inlet without exceeding any limits of the system.

A visual inspection is used to identify if the PRV is installed properly, is correct for the application, and doesn’t have apparent problems.

Check the nameplate information to verify that the valve is installed on the proper service. A missing nameplate requires immediate addressing.

If the valve is installed on gas/vapor service, the nameplate’s capacity will indicate an air capacity at standard conditions.

If the valve is on liquid service, the nameplate will indicate a water capacity.

Check the seal wire. A broken seal wire indicates that an unqualified person has adjusted the set pressure this also removes any warranty the valve had.

The following general procedure is recommended for the disassembling of a Mercer 8100 Series PRV.; Non-standard, “special”, configurations are possible and these instructions may not be reflective of them; a special configuration is indicated by a special code at the end of the PRV’s part number.; Always make sure there is no pressure in the system prior to removing a PRV.

These instructions are divided into two sections: 1” Body and 2” Body.

1. Cut and remove the seal wire and unscrew the cap to expose the adjustment screw.

i) Go to "c" if the valve is a lift lever configuration.

2. Loosen the lock nut from the adjustment screw.

3. Relieve the compression on the spring by turning the adjustment screw counter clockwise.; This is important so that components will not spring out and pose a hazard.; If the adjustment screw begins to appear as residing back into the bonnet during the relieving of the preload, then the spring compression has been completely removed and the adjustment bushing is beginning to re-compress the spring.

4. Rigidly support the body to prevent movement during disassembly.

5. Unscrew the inlet base using the appropriate wrenching flats.; 6. Remove the set spring and discard the disk subassembly.