Mercer Valve Pressure Relief Valve 91-28E51T11I1

Warning: This inspection requires trained personnel with PPE!

Refer to NB-18 for ASME BPVC certified pressure relief valves and correct set pressure definition

Use nitrogen or compressed air for gas/vapor service and water for liquid service

Set pressure discrepancy can vary outside of ASME tolerances if incorrect fluid is used

Rate of system pressure increase should be slow when within 15% of the set pressure

Pressure increase rate should not exceed 2 psi/sec (15 kPa/sec) within this range

Slow pressure increase helps to accurately read the pressure gauge

Common set pressure definitions: 'Pop' - a crisp pop sound from the valve; 'First Audible Sound' - the first sound heard from the outlet of the valve; 'First Steady Stream' - a continuous stream from the outlet of the valve

Check the set pressure definition from NB-18

Warning: This procedure requires trained personnel!

Are two pressure gauges used for testing?

Are the gauges reading identical values within their respective tolerances?

Select the type of the first gauge

Select the type of the second gauge

Does the analog gauge respond to pressure quickly and give accurate readings?

Are quick pressure increases seen on the digital gauge readings?

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

Is the portion of the gauge used selected so that the tolerance of it is more stringent than the set pressure’s tolerance?

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 9100 Series PRV

Non-standard or “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

The 9100 Series contains several different orifice sizes

For most C to G orifices, the valves are bottom entry type with the bonnet integral to the body cavity

These valves have a removable inlet base

Larger orifice sized valves are top entry types and have removable bonnets

Warning: This inspection requires trained personnel with PPE!

Seat inspected for cuts and abrasions

Seat polished and restored if minor scratches or abrasions are present

Seat replaced if deep abrasions and cuts are present

Spherical surface portion that engages the seat is clean and smooth

Spherical surface polished if minor imperfections exist