A dry diaphragm gas meter measures passing gas by repeatedly filling and emptying chambers separated by flexible diaphragms. Its index totals displaced volume at the meter’s operating conditions. Converting that reading to another reference condition is a separate calculation.
Dry Gas Meter Interactive Calculator
Enter calibrated cycle volume, counted cycles and elapsed time. Compare raw volume with a separately corrected reference volume using your supplied factors.
Equation Used
- Cycle volume is calibrated per complete repeating cycle.
- Supplied factors describe the chosen reference conversion.
- Average flow is interval volume divided by elapsed time.
- Illustrative valve sequence and chamber proportions, not a manufactured meter replica.
Correction multipliers are supplied values. Raw volume and corrected reference volume are different quantities.
Follow the gas through the cutaway
The drawing exposes two diaphragm sections, each separating a pair of chambers. The blue side is expanding and receiving gas; the amber side is shrinking and delivering gas to the outlet. At the stroke end their roles reverse.
Above each pair, a hollow changeover cup joins the exhausting chamber port to the middle outlet port. The other chamber port is exposed to the inlet region. This functional valve view makes the flow direction visible rather than implying that gas passes through the diaphragm.
Real diaphragm meters connect their moving diaphragms to valve timing and an index through mechanical linkage. That linkage is housed behind the index in this cutaway. The cutaway leaves the index linkage enclosed and focuses on the chamber and valve sequence.
Two sinusoidal diaphragm motions, separated by one-quarter cycle, illustrate the chamber sequence. Instantaneous valve changeover and the chamber proportions are explanatory assumptions, not a reproduction of a specific meter’s timing. The index display shows the entered interval total, while the animation repeats one cycle.
Calculate volume from a cycle count
Use the calibrated volume for one complete repeating cycle and the number of complete cycles counted during an observation interval. Confirm the meaning of a cycle for the particular meter or test index; an individual chamber stroke need not equal one complete meter cycle.
Cycle volume and count determine raw metered volume. The supplied temperature and pressure factors convert that volume to the chosen reference conditions, and elapsed time determines average flow. Meter capacity is not calculated.
The temperature and pressure multipliers are values supplied by the user. Leave both at 1 to compare the uncorrected reading. Applying factors here does not mean the physical meter contains a temperature or pressure corrector.
Cycle count, units and correction factors
For cycle volume Vc in cubic inches and cycle count N, raw metered volume is Vm=VcN/1728 cubic feet. The factor 1728 is 12³ cubic inches per cubic foot.
With supplied multipliers Kt and Kp, corrected volume is Vb=VmKtKp. The corresponding metric volume is Vb×0.028316846592 cubic metres. For an observation interval t in minutes, corrected average flow is 60Vb/t cubic feet per hour.
For an ideal-gas conversion with constant conditions, the temperature multiplier is Tbase/Tmeter using absolute temperatures, and the pressure multiplier is Pmeter/Pbase using absolute pressures. A compressibility conversion, where required, introduces Zbase/Zmeter as well. This tool does not determine those conditions or a compressibility factor. The user must supply factors appropriate to the measurement and intended reference.
In the illustrative chamber model, each of four chamber sweeps displaces Vc/4 per complete repeating cycle. That normalization explains the cycle count; it is not a way to infer a real meter’s calibration from the dimensions of this drawing.
Default observation
At 140 in³ per cycle and 500 counted cycles, raw volume is 70000 in³, or about 40.5093 ft³. With both correction multipliers equal to 1, corrected volume is the same, or about 1.14709 m³.
Over 10 minutes, the corrected average is about 243.056 ft³/h. Doubling the observation time while keeping the counted cycles unchanged halves the average flow; it does not change the measured interval volume.
Changing the temperature multiplier to 0.95 changes corrected volume to about 38.4838 ft³ while raw metered volume remains 40.5093 ft³. Setting the cycle count to zero makes both volumes and the flow zero and stops the animation.
What this model does not determine
Cycle volume must come from the relevant calibration or meter information. The drawing does not establish accuracy, leakage, pressure loss, maximum flow or a maintenance interval.
Average flow over the chosen interval is different from the pulsating instantaneous chamber flow. Playback is slowed and limited to a readable speed; it is not a real-time test.
Reference-condition correction requires consistent absolute temperature and pressure conventions. Do not use gauge pressure directly as an absolute-pressure ratio. If conditions vary significantly during the observation, a single pair of factors may not describe the whole interval.
This tool calculates interval volume and average flow from the entered count and conversion factors. A particular meter’s operating range and capacity must come from its specifications.
Dry gas meter questions
Why are there four chambers but only two diaphragms?
Each diaphragm separates two gas spaces. One side expands while the other side contracts.
Does gas cross the diaphragm?
No. Each side has a valve-controlled port. The membrane separates the gas spaces.
Why do correction factors not move the diaphragms farther?
They convert the measured volume to a reference condition. They do not change the meter’s physical stroke or raw cycle count.
Why does the index stay fixed during playback?
It displays the total for the entered observation interval. The repeating animation is a separate single-cycle illustration, not an ongoing measurement of new gas.
Is the valve motion exact for my meter?
No. The cutaway shows functional routing and assumed phasing. Actual valve timing, calibration and linkage geometry are model-specific.
References and model basis
American Meter, US4706496A: Diaphragm gas meter describes a four-chamber diaphragm meter, its valve table, changeover valves and linkage. It informs the component relationships, not the dimensions or timing of this explanatory cutaway.
Honeywell Absolute-ENCODER AE5 distinguishes measured volume at operating conditions and the mechanical connection to the diaphragm meter index.
Hiscox, Mechanical Movements, Powers, Devices and Appliances, movement 1621, printed page 390, illustrates a historical dry gas meter and registering train. The equations convert calibrated cycle counts into raw volume, reference volume and interval-average flow.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
