Handbook 44 – 2020 3.33. Hydrocarbon Gas Vapor-Measuring Devices

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Table of Contents

Page

Section 3.33. Hydrocarbon Gas Vapor-Measuring Devices......................................... 3-63

A. Application ....................................................................................................................................................................3-63

A.1. General. ................................................................................................................................................................3-63

A.2. Exceptions. ..........................................................................................................................................................3-63

A.3. Additional Code Requirements........................................................................................................................3-63

S. Specifications ................................................................................................................................................................3-63

S.1. Design of Indicating and Recording Elements and of Recorded Representations.................................. 3-63

S.1.1. Primary Elements................................................................................................................................3-63

S.1.2. Graduations..........................................................................................................................................3-64

S.1.3. Indicators..............................................................................................................................................3-64

S.2. Design of Measuring Elements........................................................................................................................3-65

S.2.1. Pressure Regulation............................................................................................................................3-65

S.2.2. Provision for Sealing..........................................................................................................................3-65

S.2.3. Maintenance of Vapor State..............................................................................................................3-65

S.2.4. Automatic Temperature Compensation..........................................................................................3-65

S.3. Design of Discharge Lines................................................................................................................................3-65

S.3.1. Diversion of Measured Vapor. .........................................................................................................3-65

S.4. Marking Requirements......................................................................................................................................3-66

S.4.1. Limitations of Use. .............................................................................................................................3-66

S.4.2. Discharge Rates...................................................................................................................................3-66

S.4.3. Temperature Compensation..............................................................................................................3-66

S.4.4. Badge. ...................................................................................................................................................3-66

N. Notes................................................................................................................................................................................3-66

N.1. Test Medium. ......................................................................................................................................................3-66

N.2. Temperature and Volume Change...................................................................................................................3-66

N.3. Test Drafts. ..........................................................................................................................................................3-66

N.4. Test Procedures...................................................................................................................................................3-66

N.4.1. Normal Tests. ......................................................................................................................................3-66

N.4.2. Special Tests........................................................................................................................................3-67

N.4.3. Repeatability Tests.............................................................................................................................3-67

N.5. Temperature Correction. ...................................................................................................................................3-67

N.6. Frequency of Test...............................................................................................................................................3-67

T. Tolerances......................................................................................................................................................................3-67

T.1. Tolerance Values on Normal Tests and on Special Tests Other Than Low-Flame Tests...................... 3-67

T.2. Repeatability........................................................................................................................................................3-68

UR. User Requirements......................................................................................................................................................3-68

UR.1. Installation Requirements. ................................................................................................................................3-68

UR.1.1. Capacity Rate. .....................................................................................................................................3-68

UR.1.2. Leakage. ...............................................................................................................................................3-68

UR.2. Use Requirements. .............................................................................................................................................3-68

UR.2.1. Automatic Temperature Compensation..........................................................................................3-68

UR.2.2. Invoices. ...............................................................................................................................................3-68

UR.2.3. Correction for Elevation. ...................................................................................................................3-69

UR.2.4. Valves and Test Tee............................................................................................................................3-69

UR.2.5. Use of Auxiliary Heated Vaporizer Systems. ................................................................................3-69
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Handbook 44 – 2020 3.33. Hydrocarbon Gas Vapor-Measuring Devices

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Section 3.33. Hydrocarbon Gas Vapor-Measuring Devices1

A. Application

A.1. General. – 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. Exceptions. – This code does not apply to:

(a) Liquid-measuring devices used for dispensing liquefied petroleum gases in liquid form. (Also see 

Section 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. (Also see Section 3.37. Code for Mass Flow Meters.)

(Added 1994)

A.3. Additional Code Requirements. – In addition to the requirements of this code, Hydrocarbon Gas VaporMeasuring Devices shall meet the requirements of Section 1.10. General Code.

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. – 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 280 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 ft3/h); and

(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)

 1Title changed 1986.
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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:

(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 the:

(a) width of the narrowest graduation;* and

[*Nonretroactive as of January 1, 2002]

(Amended 2001)

(b) 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).
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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. – 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

(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 Pa or psia

GP = Gauge pressure in Pa or psig

NGP = Normal gauge pressure in Pa 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. – For devices or systems in which the configuration or calibration parameters 

can be changed by use of a removable digital storage device, security shall be provided for those parameters as 

specified in G-S.8.2. Devices and Systems Adjusted Using Removable Digital Storage Devices. For parameters 

adjusted using other means, the following applies.

Adequate provision shall be made for applying security seals in such a manner that no adjustment or interchange 

can be made of any measurement element.

(Amended 2019)

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.
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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 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.

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 U.S. Customary 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)
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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.4.2. 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. Normal Tests 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 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.4.3. 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. When 

conducting the tests, the minimum discharge rate shall be the minimum flow rate marked on the device or at least 

20% of the marked capacity rate, whichever is less, and the maximum discharge rates shall not exceed the capacity 

rate as marked by the manufacturer.

Note: The repeatability test will not be performed at the low-flame flow rate for these devices as the time required would be 

unrealistic.

(Renumbered and Amended 2019)

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

(Amended 1981 and 2003)
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Table T.1. 

Accuracy Classes and Tolerances for Hydrocarbon Gas Vapor-Measuring Devices

Accuracy Class Application Acceptance 

Tolerance

Maintenance 

Tolerance

3.0 Gases at low pressure

(for example, LPG vapor)

Overregistration 1.5 % 1.5 %

Underregistration 3.0 % 3.0 %

(Added 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. Also see N.4.3. Repeatability Test.

(Added 2002) (Amended 2019)

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.

UR.2.2. Invoices. – A customer purchasing hydrocarbon gas measured by a vapor meter 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.
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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. Corrections for Altitude, Metric Units 

or Table 2. Corrections for Altitude, U.S. Customary Units 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 up-stream of the meter.

(Added 1990)
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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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Table 2. 

Corrections for Altitude, U.S. Customary 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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