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Technical Facts

Percent Proof = Volume indicated by reference standard Volume indicated by meter X 100
Percent Accuracy= Volume indicated by meter Volume indicated by reference standard X 100
Percent Correction= Volume indicated by meter - Volume indicated by reference standard Volume indicated by meter X 100
Percent Correction= Volume indicated by meter - Volume indicated by reference standard Volume indicated by reference standard X 100
Rangeability= Maximum hourly flow rate Minimum hourly flow rate  
  1. MOUNTING ORIENTATION

    A Romet meter can be installed in either the vertical or horizontal position. However, the preferred orientation is the vertical (forward flow) position. In this position, accidental delivery of certain contaminants can be usually expelled more easily through the meter.

  2. BYPASS LINE

    The installation of a bypass line placed around a meter, whether temporary or permanent, will permit maintenance and/or servicing of a meter without disrupting the gas flow to the customer. This will help reduced certain costs and any inconveniences to the customer. If gas theft is a matter of concern, consideration should be given to installing locking valves, security seals and/or tamper proof exterior hardware.

  3. PIPING RESTRICTIONS

    As a general rule of thumb, straight unrestricted piping should be maintained for a minimum distance of three pipe diameters on either side of the meter. This practice should prevent any possible reduction in the meter accuracy due to turbulence and back pressure caused by other gas devices such as regulators, valves, filters, pipe elbows, etc..

  4. WORKING CLEARANCES

    Clearance space for the removal of batteries, meter module, or any other auxiliary device should be considered in the station design.

  5. STRAINERS AND FILTERS

    At the very minimum, a strainer should be installed upstream from the meter to prevent accidental delivery of course contaminants (i.e. weld beads, pipe scale, stones, tap shavings, etc.) from entering the meter. A cartridge type filter is particularly important in protecting a meter when finer contaminants such as grit, pipe dust, valve grease, pipe paste, gum, moisture, etc. could cause meter damage.

  6. GAS QUALITY

    Generally speaking, natural gas is a mixture of hydrocarbons (methane gas being the main constituent) and noncombustible substance in a gaseous state.

    The amount of each component found in a gas mixture can significantly affect meter station operations including measurement. Water vapor for example when present in large amounts can produce highly acidic compounds that may be very corrosive to various parts of the meter station.

    Therefore, the cleaner the gas used (i.e. correct gas quality specified) the longer the metering device will operate correctly.

  7. ADVERSE ENVIRONMENT

    The meter should be built and/or protected against adverse environmental conditions (both internal and/or external). Romet should be consulted before a Romet metering device is to be installed in such conditions.

  8. UPSTREAM VALVES

    Non-lubricated valves are recommended upstream from the meter to prevent possible valve grease contamination which may slow or stop meter functions. If greasing of valves is required, the manufacturer’s recommended amount of grease should be applied (i.e. do not over grease).

  9. METER COMPRESSION

    If the meter is operating at low pressure (<10 IWC or 22 mbar) and the load is shut off suddenly, downstream compression by the meter may occur. A sufficient length of pipe between the meter and the pilot load should be installed to provide a sufficient displaced volume.

  10. SUDDEN LOADS

    On application where a full load maybe turned on suddenly (not recommended), a restricting device should be installed downstream from the meter to prevent overspeeding and rapid pressurization of the meter. The restricting device should slow the gas flow to an acceptable flow and pressurization rate that will not exceed the meter’s rated capacity (Qmax).

The following procedure can be used to calculate the specific gravity of a gas relative to that of air (1.00 at standard temperature and pressure). The example used is for natural gas (ng) of a fixed composition with no distillates.

Molecular weight of air

To find the molecular weight of air, make the following assumptions and calculations:

79% nitrogen (molecular weight = 28) in air: 0.79 x 28 = 22.1

21% oxygen (molecular weight = 32) in air: 0.21 x 32 = 6.7

Therefore, the molecular weight of air, MW a , is 22.1 + 6.7 = 28.8 *

Molecular weight of natural gas

To find the molecular weight of natural gas (ng), make the following assumptions and calculations:

90% methane (molecular weight = 16) in natural gas: 0.90 x 16 = 14.4

5% ethane (molecular weight = 30) in natural gas: 0.05 x 30 = 1.5

5% nitrogen (molecular weight = 28) in natural gas: 0.05 x 28 = 1.4

Therefore, the molecular weight of natural gas, MW ng , is 14.4 + 1.5 + 1.4 = 17.3

Specific gravity of natural gas

The specific gravity of natural gas compared with that of air is thus MW ng /MW a = 17.3/28.8 = 0.60 **

*Note: Ideal molecular weight of air = 28.9644

** Note: Published values of the specific gravity of natural gas range from about 0.554 to about 0.87. Variation in natural gas composition by location accounts for the different values.

1 bar = 100 kPa
1 bar = 14.50 Psia
1 Psia = 0.06897 bar
1 Psia = 6.89655 kPa
1 Psia = 27.72977 inWC
1 Psia = 6.89474 kPa
1 Psia = 51.71493 mmHg
1 kPa = 7.49884 mmHg
1 kPa = 4.02091 inWC
1 kPa = 0.145038 PSIA
1 mmHg = 0.5362043 inWC
1 mmHg = 0.01934 kPa
1 mmHg = 0.13335 kPa
1 inWC = 0.036062 Psia
1 inWC = 1.86496 mmHg
1 inWC = 0.2487 kPa
Gravity = 0.550 to 0.900
Mol % CO2 = 00.00 to 30.00
Mol % N2 = 00.00 to 10.00
Gravity = 0.550 to 0.900
Mol % CO2 = 00.00 to 30.00
Mol % H2 = 00.00 to 30.00
Combust. of gas = 00.00 to 10.00
Carbon Dioxide 00.00 to 30.00
Nitrogen 00.00 to 50.00
Methane 50.00 to 99.99
Ethane 00.00 to 20.00
Propane 00.00 to 05.00
Water 00.00 to 00.02
Hydrogen Sulphide 00.00 to 01.00
Hydrogen 00.00 to 10.00
Carbon Monoxide 00.00 to 03.00
Oxygen 00.00 to 05.00
iso-Butane 00.00 to 01.50
n-Butane 00.00 to 01.50
iso-Pentane 00.00 to 00.50
n-Pentane 00.00 to 00.50
n-Hexane 00.00 to 00.10
n-Heptane 00.00 to 00.05
n-Octane 00.00 to 00.05
n-Nonane 00.00 to 00.05
n-Decane 00.00 to 00.50
Helium 00.00 to 00.05
Argon 20.000 to 48.000
Imperial = 10.00 Psi to 16.00 Psi
Metric = 0.70000 bar to 1.10000 bar
Metric = 70.000 kPa to 110.000 kPa
14.73 psia
1.01325 bar
101.325 kPa
Imperial = 60°F
Metric = 0°C, 15°C, 20°C