Mercer Valve Pressure Relief Valve 81-12151V18G11

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 accumulation

External Surface free from damage

Valve Tag information corresponds to the service conditions

Set pressure, CDTP, and capacity in appropriate unit of measure for the service fluid verified

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.

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.

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 5psi (34.5kPa) 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 Co. Inc. 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 any leakage is observed.

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

There are several methods used in testing for leakage.

The following general procedure is recommended for the inspection of an 8100 Series PRV.

New parts should be inspected.

1. Inspect the seat for cuts and abrasions. The seat is the non-metallic element in the nozzle subassembly.

a) If there are only minor scratches or abrasions, the seat may be polished and restored.

b) Polish the seat area lightly with a fine grade abrasive pad. Be careful not to damage the soft seat.

c) If the seat is damaged with deep abrasions and cuts, it should be replaced.

2. Referring to Figure 29, measure the diameter Ds of the nozzle. This diameter must be in the range of values listed in Table

ORIFICE SIZE - ½", NOZZLE DIAMETER Ds, in (mm), 0.620 (15.75) - MINIMUM, 0.622 (15.80) - MAXIMUM

ORIFICE SIZE -¾", NOZZLE DIAMETER Ds, in (mm) 0.914 (23.22) - MINIMUM, 0.916 (23.27) - MAXIMUM