Pressure Instruments – Specific Requirements

Pressure Gages

Direct-mounted pressure gages may be installed with a ¾-inch root valve that meets the piping standards or with proprietary pressure gage block and bleed valves or approved equivalent. See Standard Drawings GB-J1143 and GB-J1144.

Remote-mounted pressure gages should be installed with a ¾-inch root valve that meets the piping standards. See Standard Drawing GB-J1146.

Pressure Gages

Direct-mounted pressure gages may be installed with a ¾-inch root valve that meets the piping standards or with proprietary pressure gage block and bleed valves or approved equivalent. See Standard Drawings GB-J1143 and GB-J1144. Remote-mounted pressure gages should be installed with a ¾-inch root valve that meets the piping standards. See Standard Drawing GB-J1146.

Pressure Switches

Facilities for testing alarms and shutdowns should include but not be limited to:
• Field High Pressure Switch. A pressure gage on the switch process lead and a valved connection should be provided to permit testing with a portable pressure source. See Standard Drawings GB-J1146 and GB-J1147
• Field Low Pressure Switch. A pressure gage on the switch process lead and an atmospheric bleed connection should be provided to bleed off pressure and permit testing against the pressure gage reading. In LPG, high H2S, and other hazardous services, the bleed should be piped to the relief system or another safe place. See Standard Drawings GB-J1146 and GB-J1147

Draft Gages

See Standard Drawing GB-J1148 for typical installation.

Automatic Pump Starters

The process connection for a pressure-operated automatic pump starter (APS) should be made between the prime pump unit discharge and its check valve (first valve).

The APS pressure pilot should be located at the process connection if the steam APS control valve is visible from that location. If the steam valve is not visible from the process connection, the pressure pilot should be located where the steam valve can be observed.

Steam-driven APS pumps are used in refineries where the process must keep running through power failures. Most other plants use a pressure switch on the common discharge line and select between the main pump and a standby motor driven pump with HOA (Hand-Off-Auto) switches.

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