Mercer Valve Pressure Relief Valve 91-12M42PA7LC

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!

PRV placed in arbor press upside down

PRV's set spring has initial tension

Rod placed through the inlet without damaging the seat or touching the side walls of the nozzle insert

Measurement of the displacement of the disk from the closed position to the mechanical stops at the fully open position

Shaft of the arbor press pressing against the rod sticking out of the valve inlet base

Measurement of the displacement of the arbor press shaft using a dial indicator

Enter the minimum lift for certified PRVs from NB-18 publication

Warning: This procedure requires trained personnel with PPE!

Valves transported to the shop?

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 (dial) gauge respond to pressure quickly and give accurate readings?

Are quick pressure increases seen on the digital gauge readings?

Do the test gauges 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?