Mercer Valve Pressure Relief Valve 91-12HQ3NA7XC

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

Mobile testing units are similar to offsite testing

The valve is removed from the application

This enables a thorough inspection

Mobile testing units can save time because transporting the valve isn’t necessary

Mobile test units are often not set up to test all types and sizes

The testing equipment on a mobile test unit can vary

Some mobile test units have test stands similar to an offsite test stand, allowing for larger valves to be tested accurately

Other mobile test units are set up only for smaller valves

In each case, 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;

Warning: This procedure requires trained personnel with PPE!

Place the PRV in an arbor press upside down

Does the PRV's set spring have initial tension?

Place a rod through the inlet that touches the disk. The rod should fit in the inlet base without damaging the seat or touching the side walls of the nozzle insert.

The lift is the measurement of the displacement of the disk from the closed position to the mechanical stops at the fully open position.

The shaft of the arbor press will press against the rod sticking out of the valve inlet base.

Apply a slight force using the arbor press to find the lift.

Enter the displacement of the arbor press shaft as measured by the dial indicator. This is the PRV's lift.

The minimum lift for certified PRVs can be found in NB-18 publication, which is located on the National Board website www.nationalboard.org.

Warning: This procedure requires trained personnel with PPE!

Valves removed from the units and brought to the shop

Valve completely tested and inspected in the shop

Volume of pressure during testing

Pressure losses to the gauges during testing

Supply line pressure during testing

Proper assembly of a test bench

Note: The main disadvantage in offsite testing is time

Warning: This inspection requires trained personnel with PPE!

Refer to NB-18 for set pressure definition and other valve characteristics

Use correct fluid for testing: nitrogen or compressed air for gas/vapor service, water for liquid service

Setting procedures should be in accordance with ASME PTC 25

Slowly increase the pressure when within 15% of the set pressure, not more than 2 psi/sec

Common set pressure definitions: 'Pop', 'First Audible Sound', 'First Steady Stream'

Valve connected to a test fixture?

Enter the pressure at which the valve opens

Did the valve open at less than 1.5 times the expected set pressure?