Handbook 44 - 2007 3.33. Hydrocarbon Gas Vapor-Measuring Devices 

Section 3.33. Hydrocarbon Gas Vapor-Measuring Devices1

A. Application 

A.1. - This code applies to devices used for the measurement of hydrocarbon gas in the vapor state, such as propane, 

propylene, butanes, butylenes, ethane, methane, natural gas and any other hydrocarbon gas/air mix. 

(Amended 1984, 1986, 1988, and 1991) 

A.2. - This code does not apply to: 

(a) Liquid-measuring devices used for dispensing liquefied petroleum gases in liquid form (see Sec. 3.32; Code for 

Liquefied Petroleum Gas and Anhydrous Ammonia Liquid-Measuring Devices). 

(b) Natural, liquefied petroleum, and manufactured-gas-vapor meters when these are operated in a public utility 

system. 

(c) Mass flow meters (see Sec. 3.37. Code for Mass Flow Meters) 

(Added 1994) 

A.3. - See also Sec. 1.10; General Code requirements. 

S. Specifications 

S.1. Design of Indicating and Recording Elements and of Recorded Representations.

S.1.1. Primary Elements.

S.1.1.1. General. - A device shall be equipped with a primary indicating element and may also be equipped 

with a primary recording element. 

S.1.1.2. Units. - A volume-measuring device shall indicate, and record if equipped to record, its deliveries in 

terms of cubic meters or cubic feet, or multiple or decimal subdivisions of cubic meters or cubic feet. 

(Amended 1972 and 1991) 

S.1.1.3. Value of Smallest Unit. - Volume-Measuring Devices: The value of the smallest unit of indicated 

delivery, and recorded delivery if the device is equipped to record, shall not exceed: 

(a) 1 m3

 (1000 dm3) (100 ft3) when the maximum rated gas capacity is less than 100 m3/h (10 000 ft3/h); 

(b) 10 m3 (1000 ft3) when the maximum rated gas capacity is 280 m3/h (10 000 ft3/h) up to, but not 

including, 1700 m3

/h (60 000 ft 3/h); 

(c) 100 m3

 (10 000 ft3) when the maximum rated gas capacity is 1700 m3/h (60 000 ft3/h) or more. 

(Amended 1972, 1988, and 1991) 

S.1.1.4. Advancement of Indicating and Recording Elements. - Primary indicating and recording elements 

shall advance digitally or continuously and be susceptible to advancement only by the mechanical operation of 

the device. 

S.1.1.5. Proving Indicator. - Devices rated less than 280 m3

/h (10 000 ft3/h) gas capacity shall be equipped 

with a proving indicator measuring 0.025, 0.05, 0.1, 0.2, or 0.25 m3

 per revolution, (1, 2, 5, or 10 ft3 per 

revolution) for testing the meter. Devices with larger capacities shall be equipped as follows: 

 

1

Title changed 1986. 

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3.33. Hydrocarbon Gas Vapor-Measuring Devices Handbook 44 - 2007 

(a) Devices rated 280 m3

 (10 000 ft3) up to but not including 1700 m3/h (60 000 ft3/h) gas capacity shall be 

equipped with a proving indicator measuring not greater than 1 m3

 (100 ft3) per revolution. 

(b) Devices rated 1700 m3

/h (60 000 ft3/h) gas capacity or more shall be equipped with a proving indicator 

measuring not more than 10 m3

 (1000 ft3) per revolution. 

The test circle of the proving indicator shall be divided into ten equal parts. Additional subdivisions of one 

or more of such equal parts may be made. 

(Amended 1973 and 1988) 

S.1.2. Graduations.

S.1.2.1. Length. - Graduations shall be so varied in length that they may be conveniently read. 

S.1.2.2. Width. - In any series of graduations, the width of a graduation shall in no case be greater than the 

width of the minimum clear interval between graduations, and in no case should it exceed 1.0 mm (0.04 in) for 

indicating elements and 0.5 mm (0.02 in) for proving circles. 

S.1.2.3. Clear Interval Between Graduations. - The clear interval shall be not less than 1.0 mm (0.04 in). If 

the graduations are not parallel, the measurement shall be made: 

(a) along the line of relative movement between the graduations at the end of the indicator, or 

(b) if the indicator is continuous, at the point of widest separation of the graduations. 

S.1.3. Indicators.

S.1.3.1. Symmetry. - The index of an indicator shall be symmetrical with respect to the graduations, at least 

throughout that portion of its length associated with the graduations. 

S.1.3.2. Length. - The index of an indicator shall reach to the finest graduations with which it is used. 

S.1.3.3. Width. - The width of the index of an indicator in relation to the series of graduations with which it is 

used shall be not greater than: 

(a) the width of the narrowest graduation* , and 

[*Nonretroactive as of January 1, 2002]

(Amended 2001) 

(b) the width of the minimum clear interval between graduations. 

When the index of an indicator extends along the entire length of a graduation, that portion of the index of the 

indicator that may be brought into coincidence with the graduation shall be of the same width throughout the 

length of the index that coincides with the graduation. 

S.1.3.4. Clearance. - The clearance between the index of an indicator and the graduations shall in no case be 

more than 1.5 mm (0.06 in). 

S.1.3.5. Parallax. - Parallax effects shall be reduced to the practicable minimum. 

S.2. Design of Measuring Elements.

S.2.1. Pressure Regulation. - Except when measured as a retail motor fuel, the vapor should be measured at a 

normal gauge pressure (psig) of: 

(Amended 1991) 

(a) 2740 Pa ± 685 Pa (11 in of water column (0.40 psig) ± 2.75 in of water column (0.10 psig)) for liquefied 

petroleum gas vapor; or 

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Handbook 44 - 2007 3.33. Hydrocarbon Gas Vapor-Measuring Devices 

(b) 1744 Pa ± 436 Pa (7 in of water column (0.25 psig) ± 1.75 in of water column (0.06 psig)) for natural and 

manufactured gas. 

When vapor is measured at a pressure other than what is specified above for the specific product, a volume multiplier 

shall be applied within the meter or to the billing invoice based on the following equation: 

AAP + GP 

VPM = AAP + NGP 

Where: 

VPM = Volume pressure multiplier 

AAP = Assumed atmospheric pressure in psia 

GP = Gauge pressure in pascal or psig 

NGP = Normal gauge pressure in pascal or psig 

The assumed atmospheric pressure is to be taken from Tables 2 and 2M. 

When liquefied petroleum gas vapor is measured at a pressure of 6900 Pa (1 psig) or more, the delivery pressure shall 

be maintained within ± 1725 Pa (± 0.25 psig). 

Pressure variations due to regulator lock off shall not increase the operating pressure by more than 25 %. 

(Amended 1980, 1984, and 1991) 

S.2.2. Provision for Sealing. - Adequate provision shall be made for applying security seals in such a manner that 

no adjustment or interchange may be made of any measurement element. 

S.2.3. Maintenance of Vapor State. - A device shall be so designed and installed that the product being measured 

will remain in a vapor state during passage through the meter. 

S.2.4. Automatic Temperature Compensation. - A device may be equipped with an adjustable automatic means 

for adjusting the indication and registration of the measured volume of vapor product to the volume at 15 °C (60 °F). 

S.3. Design of Discharge Lines

S.3.1. Diversion of Measured Vapor. - No means shall be provided by which any measured vapor can be diverted 

from the measuring chamber of the meter or the discharge line therefrom. 

S.4. Marking Requirements.

S.4.1. Limitations of Use. - If a device is intended to measure accurately only products having particular properties, 

or to measure accurately only under specific installation or operating conditions, or to measure accurately only when 

used in conjunction with specific accessory equipment, these limitations shall be clearly and permanently stated on 

the device. 

S.4.2. Discharge Rates. - A volume-measuring device shall be marked to show its rated gas capacity in cubic meters 

per hour or cubic feet per hour. 

S.4.3. Temperature Compensation. - If a device is equipped with an automatic temperature compensator, this shall 

be indicated on the badge or immediately adjacent to the badge of the device and on the register. 

S.4.4. Badge. - A badge affixed in a prominent position on the front of the device shall show the manufacturer's 

name, serial number and model number of the device, and capacity rate of the device for the particular products that 

it was designed to meter as recommended by the manufacturer. 

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3.33. Hydrocarbon Gas Vapor-Measuring Devices Handbook 44 - 2007 

N. Notes 

N.1. Test Medium. - The device shall be tested with air or the product to be measured. 

(Amended 1991) 

N.2. Temperature and Volume Change. - Care should be exercised to reduce to a minimum any volume changes. The 

temperature of the air, bell-prover oil, and the meters under test should be within 1 °C (2 °F) of one another. The devices 

should remain in the proving room for at least 16 hours before starting any proving operations to allow the device 

temperature to approximate the temperature of the proving device. 

N.3. Test Drafts. - Except for low-flame tests, test drafts shall be at least equal to one complete revolution of the largest 

capacity proving indicator, and shall in no case be less than 0.05 m3

 or 2 ft3. All flow rates shall be controlled by suitable 

outlet orifices. 

(Amended 1973 and 1991) 

Table 1. 

Capacity of Low-Flow Test Rate Orifices 

With Respect to Device Capacity

Metric Units Inch-Pound Units 

Rated Capacity Low-Flow Test Rate Rated Capacity Low-Flow Test Rate 

Up to and including 7 m3/h 0.007 m3/h Up to and including 250 ft3/h 0.25 ft3/h 

Over 7 m3/h up to and including 

14 m3

/h 0.014 m3

/h Over 250 ft3

/h up to and 

including 500 ft3

/h 0.50 ft3

/h 

Over 14 m3/h 0.1 % of capacity rate Over 500 ft3/h 0.1 % of capacity rate 

N.4. Test Procedures. - If a device is equipped with an automatic temperature compensator, the proving device reading 

shall be corrected to 15 °C (60 °F), using an approved table. 

(Amended 1972) 

N.4.1. Normal Tests. - The normal test of a device shall be made at a rate not to exceed the capacity rate given on 

the badge of the meter. 

(Amended 1988) 

N.4.1.1. Automatic Temperature Compensation. - If a device is equipped with an automatic temperature 

compensator, the quantity of the test draft indication of the standard shall be corrected to 15 °C (60 °F). 

N.4.1.2. Repeatability Tests. - Tests for repeatability should include a minimum of three consecutive test drafts 

of approximately the same size and be conducted under controlled conditions where variations in factors, such as 

temperature pressure, and flow rate are reduced to the extent that they will not affect the results obtained. 

(Added 2002) 

N.4.2. Special Tests. - "Special" tests shall be made to develop the operating characteristics of a device and any 

special elements and accessories attached to or associated with the device. Any test except as set forth in N.4.1. shall 

be considered a special test. 

N.4.2.1. Slow Test. - The device shall be tested at a rate not less than 20 % of the marked capacity rate, or (at 

the check rate) not less than the minimum flow rate if marked on the device, whichever is less. 

(Amended 1988) 

N.4.2.2. Low-Flame Test. - The device shall be tested at an extremely low-flow rate as given in Table 1. The 

test shall consist of passing air at a pressure of 375 Pa (1.5 in water column) through the meter for not less than 

60 minutes. The meter shall continue to advance at the conclusion of the test period. 

(Amended 1990 and 1991) 

N.4.2.3. Pressure Regulation Test. - On devices operating at a pressure of 6900 Pa (1 psig) or more, a pressure 

regulation test shall be made at both the minimum and maximum use load to determine the proper operation of 

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Handbook 44 - 2007 3.33. Hydrocarbon Gas Vapor-Measuring Devices 

the regulator and the proper sizing of the piping and dispensing equipment. These tests may include a test of 

24 hours during which the pressure is recorded. 

(Added 1984) 

N.5. Temperature Correction. - Corrections shall be made for any changes in volume resulting from the difference in 

air temperatures between time of passage through the device and time of volumetric determination in the proving device. 

N.6. Frequency of Test. - A hydrocarbon gas vapor-measuring device shall be tested before installation and allowed to 

remain in service for 10 years from the time last tested without being retested, unless a test is requested by: 

(a) the purchaser of the product being metered, 

(b) the seller of the product being metered, or 

(c) the weights and measures official. 

T. Tolerances 

T.1. Tolerance Values on Normal Tests and on Special Tests Other Than Low-Flame Tests. - Maintenance and 

acceptance tolerances for normal and special tests for hydrocarbon gas vapor-measuring devices shall be as shown in 

Table T.1. 

(Amended 1981 and 2003) 

T.2. Repeatability. - When multiple tests are conducted at approximately the same flow rate and draft size, the range of 

the test results for the flow rate shall not exceed 0.9 % and the results of each test shall be within the applicable tolerance. 

See also N.4.1.2. 

(Added 2002) 

Table T.1. Accuracy Classes and Tolerances for Hydrocarbon Gas Vapor-Measuring Devices 

Accuracy Class Application Acceptance 

Tolerance

Maintenance 

Tolerance

Overregistration 1.5 % 1.5 % 

3.0 Gases at low pressure 

(for example, LPG vapor) Underregistration 3.0 % 3.0 % 

(Added 2003) 

UR. User Requirements 

UR.1. Installation Requirements.

UR.1.1. Capacity Rate. - A device shall be so installed that the actual maximum flow rate will not exceed the 

capacity rate except for short durations. If necessary, means for flow regulation shall be incorporated in the 

installation, in which case this shall be fully effective and automatic in operation. 

UR.1.2. Leakage. - The metering system shall be installed and maintained as a pressure-tight and leak-free 

system. 

UR.2. Use Requirements.

UR.2.1. Automatic Temperature Compensation. - A compensated device may not be replaced with an 

uncompensated device without the written approval of the weights and measures authority having jurisdiction over 

the device. 

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3.33. Hydrocarbon Gas Vapor-Measuring Devices Handbook 44 - 2007 

UR.2.2. Invoices. - A customer purchasing hydrocarbon gas measured by a vapor meter for other than motor fuel 

shall receive from the seller an invoice for each billing period. The invoice shall clearly and separately show the 

following: 

(a) The opening and closing meter readings and the dates of those readings. 

(b) The altitude correction factor. 

(c) The total cubic meters (cubic feet) billed, corrected for elevation. 

(d) The charge per cubic meter (cubic foot) after correction for elevation. 

(e) All periodic charges independent of the measured gas, such as meter charges, meter reading fees, service 

charges or a minimum charge for a minimum number of cubic meters (cubic feet). 

(f) The total charge for the billing period. 

If the vapor meter is equipped with an automatic temperature compensator, or any other means are used to 

compensate for temperature, the invoice shall show that the volume has been adjusted to the volume at 15 °C (60 °F). 

(Amended 1988 and 1991) 

UR.2.3. Correction for Elevation. - The metered volume of gas shall be corrected for changes in the atmospheric 

pressure with respect to elevation to the standard pressure of 101.56 kPa (14.73 psia). The appropriate altitude 

correction factor from Table 2M or 2 shall be used. (The table is modified from NIST Handbook 117.) 

(Amended 1988) 

Elevation correction factors (ACF) were obtained by using the following equation: 

GP of gas + AAP 

ACF = base pressure 

Where: 

GP = gauge pressure 

AAP = assumed atmospheric pressure 

base pressure = 101.560 kPa = 14.73 psia 

2740 Pa = 11 in of water column = 0.397 psig 

1744 Pa = 7 in of water column = 0.253 psig 

(Added 1988) 

UR.2.4. Valves and Test Tee. - All gas meter installations shall be provided with a shut-off valve located adjacent to 

and on the inlet side of the meter. In the case of a single meter installation utilizing a liquefied petroleum gas tank, 

the tank service valve may be used in lieu of the shut-off valve. All gas meter installations shall be provided with a 

test tee located adjacent to and on the outlet side of the meter. 

[Nonretroactive as of January 1, 1990.] 

(Added 1989) 

UR.2.5. Use of Auxiliary Heated Vaporizer Systems. - Automatic temperature compensation shall be used on 

hydrocarbon gas vapor meters equipped with an auxiliary heated vaporizer system unless there is sufficient length of 

underground piping to provide gas at a uniform temperature to the meter inlet. When required by weights and 

measures officials, a thermometer well (appropriately protected against freezing) shall be installed immediately upstream of the meter. 

(Added 1990) 

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Handbook 44 - 2007 3.33. Hydrocarbon Gas Vapor-Measuring Devices 

Table 2M. Corrections for Altitude, Metric Units

Elevation 

(meters) 

Altitude 

Correction 

Factor 

Assumed 

Atmospheric 

Pressure 

Assumed Atmospheric 

Pressure Plus 

Gauge Pressure 

2.74 kPa 

Gauge 

Pressure 

1.74 kPa 

Gauge 

Pressure 

(kPa) 2.74 kPa 

Gauge 

Pressure 

1.74 kPa 

Gauge 

Pressure 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

-50 to 

120 to 

300 to 

470 to 

650 to 

830 to 

1020 to 

1210 to 

1400 to 

1590 to 

1790 to 

2000 to 

2210 to 

2420 to 

2640 to 

2860 to 

3080 to 

3320 to 

3560 to 

3800 to 

4050 to 

4310 to 

120 

300 

470 

650 

830 

1020 

1210 

1400 

1590 

1790 

2000 

2210 

2420 

2640 

2860 

3080 

3320 

3560 

3800 

4050 

4310 

4580 

1.02 

1.00 

0.98 

0.96 

0.94 

0.92 

0.90 

0.88 

0.86 

0.84 

0.82 

0.80 

0.78 

0.76 

0.74 

0.72 

0.70 

0.68 

0.66 

0.64 

0.62 

0.60 

1.01 

0.99 

0.97 

0.95 

0.93 

0.91 

0.89 

0.87 

0.85 

0.83 

0.81 

0.79 

0.77 

0.75 

0.73 

0.71 

0.69 

0.67 

0.65 

0.63 

0.61 

0.59 

100.85 

98.82 

96.79 

94.76 

92.73 

90.70 

88.66 

86.63 

84.60 

82.57 

80.54 

78.51 

76.48 

74.45 

72.41 

70.38 

68.35 

66.32 

64.29 

62.26 

60.23 

58.20 

103.59 

101.56 

99.53 

97.50 

95.47 

93.44 

91.40 

89.37 

87.34 

85.31 

83.28 

81.25 

79.22 

77.19 

75.15 

73.12 

71.09 

69.06 

67.03 

65.00 

62.97 

60.94 

102.58 

100.54 

98.51 

96.48 

94.45 

92.42 

90.39 

88.36 

86.33 

84.29 

82.26 

80.23 

78.20 

76.17 

74.15 

72.12 

70.08 

68.05 

66.01 

63.98 

61.95 

59.92 

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3.33. Hydrocarbon Gas Vapor-Measuring Devices Handbook 44 - 2007 

Table 2. Corrections for Altitude, Inch-Pound Units

Elevation 

(feet) 

Altitude 

Correction 

Factor 

Assumed 

Atmospheric 

Pressure 

Assumed Atmospheric 

Pressure Plus Gauge 

Pressure 

11 inch 

WC 

7 inch 

WC 

(psia) 11 inch WC 

(psia) 

7 inch WC 

(psia) 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

above 

-150 to 

400 to 

950 to 

1 550 to 

2 100 to 

2 700 to 

3 300 to 

3 950 to 

4 550 to 

5 200 to 

5 850 to 

6 500 to 

7 200 to 

7 900 to 

8 600 to 

9 350 to 

10 100 to 

10 850 to 

11 650 to 

12 450 to 

13 250 to 

14 100 to 

400 

950 

1 550 

2 100 

2 700 

3 300 

3 950 

4 550 

5 200 

5 850 

6 500 

7 200 

7 900 

8 600 

9 350 

10 100 

10 850 

11 650 

12 450 

13 250 

14 100 

14 950 

1.02 

1.00 

0.98 

0.96 

0.94 

0.92 

0.90 

0.88 

0.86 

0.84 

0.82 

0.80 

0.78 

0.76 

0.74 

0.72 

0.70 

0.68 

0.66 

0.64 

0.62 

0.60 

1.01 

0.99 

0.97 

0.95 

0.93 

0.91 

0.89 

0.87 

0.85 

0.83 

0.81 

0.79 

0.77 

0.75 

0.73 

0.71 

0.69 

0.67 

0.65 

0.63 

0.61 

0.59 

14.64 

14.35 

14.05 

13.76 

13.46 

13.17 

12.87 

12.58 

12.28 

11.99 

11.69 

11.40 

11.10 

10.81 

10.51 

10.22 

9.92 

9.63 

9.33 

9.04 

8.75 

8.45 

15.04 

14.74 

14.45 

14.15 

13.86 

13.56 

13.27 

12.97 

12.68 

12.38 

12.09 

11.79 

11.50 

11.20 

10.91 

10.61 

10.32 

10.03 

9.73 

9.44 

9.14 

8.85 

14.89 

14.60 

14.30 

14.01 

13.71 

13.42 

13.12 

12.83 

12.53 

12.24 

11.94 

11.65 

11.35 

11.06 

10.76 

10.47 

10.17 

9.88 

9.58 

9.29 

9.00 

8.70 

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