A lantern-bellows dry gas meter measures gas by repeatedly filling and emptying flexible chambers. Gas pressure moves the diaphragms; their linkage turns a spindle that operates the valves and the volume register. Hiscox illustrates two pairs of bellows connected through rock shafts. The animation opens out those pairs so their alternating expansion and contraction are visible.
Lantern Bellows Dry Gas Meter Interactive Calculator
Enter the total measured volume displaced in one complete spindle cycle, the cycle rate and a running time. Watch the paired bellows move through a connected illustrative linkage. Blue chambers expand while gold chambers contract.
Equation Used
Vcycle is the total displacement in litres for one complete cycle of the entire meter, not the volume of one chamber. c is cycles per minute; t is minutes. Q is cubic metres per hour at meter conditions. The drawing uses illustrative fixed proportions and moves at the entered cycle rate. Changing displacement changes the calculated volume, not the drawing’s size. Valve ports, seals and the register gear train are omitted. Zero cycle rate gives zero flow and undefined cycle time. Leakage, pressure loss and calibration error are not calculated.
Bellows motion operates the valve and register
Each pair has a moving central diaphragm between flexible chambers. As gas fills one side, the diaphragm moves and the opposite side discharges. The diaphragm’s pivots move arms on a rock shaft. Arms above the rock shafts turn a common spindle, which slides the valve across the chamber ports and drives the dial train.
Gas supplies the motive force. The valve connects each chamber to the inlet or outlet at the appropriate part of the cycle. The register counts repeated displacement rather than measuring gas velocity through a pipe.
The illustration separates the two pairs and places their connecting rods in front of the bellows sections. Its fixed link lengths form a continuous closed motion, but they are illustrative proportions rather than dimensions for Hiscox’s meter. Chamber colours indicate expansion and contraction. Internal valve passages, seals, gear ratios and pressure-driven starting behaviour are not shown.
A historical positive-displacement gas meter
Hiscox lists this arrangement as figure 1619 in Mechanical Movements, Powers, Devices and Appliances. It belongs to the dry-meter family: flexible chambers and mechanical valves meter gas without the liquid seal used by a wet meter.
A particular meter’s usable flow range, gas compatibility, pressure rating and calibration come from that meter’s documentation. The historical drawing does not specify those ratings. Its dimensions and register gearing should not be assumed to match a modern residential meter.
Volume per cycle times cycle rate
If the complete meter displaces V litres per cycle and makes c cycles per minute, its indicated flow is Vc litres per minute, or Q=0.06Vc cubic metres per hour. Running for t minutes gives Vtotal=Vct/1000 cubic metres. One cycle takes 60/c seconds.
The same relationship can be written Q=Vcycle ncycle ×3600 when displacement is in cubic metres per cycle and rate is in cycles per second. Keep the time unit consistent: multiply a per-second rate by 3600, or a per-minute rate by 60, to obtain an hourly volume.
These are volumes at the meter’s conditions. Converting to a standard or base volume also requires the gas temperature, absolute pressure and any applicable compressibility correction. A displacement count alone does not measure gas energy or establish billing accuracy.
Two litres per cycle at six cycles per minute
For an illustrative total displacement of 2 litres per cycle and a rate of 6 cycles per minute, the meter counts 12 litres per minute. That equals 0.72 cubic metres per hour.
Over 10 minutes, it completes 60 cycles and registers 120 litres, or 0.12 cubic metres. Each cycle lasts 10 seconds. These numbers demonstrate the arithmetic; they are not the capacity or calibration of a named commercial meter.
What affects a real meter reading
Repeated chamber displacement provides a direct mechanical way to accumulate volume. The useful measurement depends on the chambers, valve sealing and register remaining consistent. Leakage can allow gas to pass without the intended displacement, while friction and pressure loss affect operation.
Geometry alone does not provide an accuracy class, starting flow, wear life or allowable pressure. Those require the particular meter’s specifications and calibration. A reading disagreement should be assessed against the meter’s documented test procedure rather than inferred from this animation.
Frequently asked questions
Why is this called a dry gas meter?
It meters with flexible chambers and valves rather than the liquid-sealed drum used in a wet meter.
What volume should I enter?
Enter the total calibrated displacement for one complete cycle of the whole meter. Do not enter a single chamber volume unless it is already the specified total cycle displacement.
Does the calculator give standard cubic metres?
No. It gives volume at meter conditions. A base-volume conversion needs temperature, absolute pressure and any relevant compressibility correction.
Are the two bellows pairs exactly 90 degrees apart?
The drawing uses a connected illustrative linkage. Hiscox’s short description does not specify a phase angle or link dimensions, so the animation does not assign a universal 90-degree setting to the historical meter.
What happens when cycle rate is zero?
The drawing stops, indicated flow and accumulated volume are zero, and cycle time is undefined.
Can this calculator determine a meter’s accuracy or capacity?
No. It multiplies the entered displacement by cycle count. Accuracy, flow limits, pressure rating and gas compatibility depend on the particular meter and its calibration.
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