Installation Diagram for D/P Transmitter (Gas Service)

Hi there,

You can download a hookup diagram from this site: http://www2.ssg.se/

Regards,

Craig

See API-RP-551.

You can't get more internationally accepted than API.

If a DP transmitter is used to measure the gas pressure (in gauge scale)
inside a vessel, the low-pressure side of the transmitter is
vented to atmosphere and the high-pressure side is connected to the vessel
through an isolating valve. The isolating valve facilitates the removal of
the transmitter.
The output of the DP transmitter is proportional to the gauge pressure of
the gas, i.e., 4 mA when pressure is 20 kPa and 20 mA when pressure is
30 kPa.

See also ANSI/ISA-S77.70-1994; Fossil Fuel Power Plant Instrument Piping Installation.

There is no diagram but text detailing mandatory requirements.

5.7 Tubing slope instrument installation
Routing of sensing lines shall ensure that the function of these lines is not affected by the
entrapment of gas (fluid-sensing line) or liquid (gas-sensing line). One of the following methods
shall be used to ensure that the sensing line is not affected: [Method (a) is preferred.]
a) For liquid measurement it is preferred that the downward slope from the tap to the
instrument of the sensing line be 1 inch or more per foot (80 mm or more per meter of
run; for gas measurement it is preferred that the upward slope from the tap to the
instrument of the sensing line be 1 inch or more per foot (80 mm or more per meter of
ANSI/ISA-S77.70-1994 15
run. Where the preferred minimum slope cannot be obtained in the two cases above,
the lines shall be installed to the maximum slope available, and in no case shall the
slope be less than ¼ inch per foot (20 mm per meter).
b) High point vents or low point drains, or both, shall be provided to ensure that all entrapped
gas or liquid can be purged from the sensing line.
c) A combination of items (a) and (b).
5.7.1 Steam and water service
Instruments shall be located below the root valve whenever possible. The purpose of running the
sensing line downward from the root valve is to limit the penetration of gas bubbles into the
system and to limit the temperature at the instrument. This location also facilitates the downward
slope of the sensing line, minimizing the need for high point vents.
5.7.2 Vacuum service
For applications in which the line pressure is negative during operation (e.g., a vacuum), the
instrument shall be located above the process connection. The purpose of this location is to
eliminate the condensed liquid in the sensing line, which could cause an error in the
measurement.
5.7.3 Air and gas service
Instruments measuring air or gas in process piping should be located above the process
connection, with the sensing line sloped downward to the process connection. This arrangement
will allow any condensed moisture to drain back into the process rather than into the instrument,
which could cause error in measurement. Otherwise, condensate pots shall be required.
5.8 Condensate pots
Condensate pots are used in the measurement of steam or other vapors for condensing the
vapor to a liquid state to minimize errors due to gas trapped in the instrument piping. Condensate
pots installed in a horizontal position should be installed level and be protected from excessive
vibration. Those installed in vertical positions are used for collecting liquid drained from a
sensing line.