Pressure Gages

It is recommended that locally mounted pressure gages be installed at the following locations to monitor the performance of equipment and pressure instruments:
• Pump and compressor discharges
• Pump and compressor interstages
• Many pump and compressor suctions
• Vessels and the vapor spaces of columns
• Nonindicating pressure transmitters
• The sensing side of each direct-operated pressure regulator and field pressure controller
• Each field pressure switch
• Each field pressure recorder
• Across filters
• Furnace fuel oil, fuel gas, and atomizing steam branch headers
• Each furnace, using a single draft gage manifolded to the convection section inlet, bridgewall, and below the stack damper
• Any application where local pressure indication is desirable, such as inlets of production manifolds

Pressure Gage Specification
Pressure gages are available in a wide range of qualities and prices. Standard quality pressure gages with blowout backs are acceptable. The Richmond Refinery has standardized on stainless steel liquid-filled pressure gages, some of the other locations use a combination of stainless steel liquid filled and unfilled gages.

For most process applications, pressure gages with an accuracy grade 2A in accordance with ANSI B40.1, Gauges—Pressure Indicating, Dial Type, Elastic Element, are acceptable. Grade 2A means the pressure gage is accurate to 0.5% of span.

Gage Construction
Pressure gages should have 4½-inch dials, ½-inch gage connections, and stainless steel movements (gages with 6-inch dials are also acceptable in most locations). The case can be cast iron or cast aluminum with a blowout plug or plastic (fiberglassreinforced polypropylene or phenolic) material with a blowout back. The gage connection should have wrench flats. The lens should be shatterproof glass. White dials with black figures and letters are standard. Other colors and graphic designs are available. Adjustment of the zero should be possible without removing the pointer from its shaft.

All pressure gages should display the tube, tip, and socket material on the front dial. The information should be imprinted by the manufacturer and should clearly describe the materials.

Pressure gage range should be selected so that the gage operates in the middle third of the scale. Overrange and underrange travel stops should be provided.

When the maximum scale reading is 1000 psig or higher, metal case gages should have solid fronts separating the dial from the movement (this is standard with plastic cases). Also, the Bourdon tube should be bored instead of drawn, and the connection between the Bourdon tube and the socket and tip should be threaded and backwelded.