A centre-guide gas holder has an inverted bell that rises and falls in a water tank. A tube attached to the bell slides along a fixed central guide. Hiscox’s figure 1616 shows this arrangement with separate fixed inlet and outlet risers. Gas pressure supports the bell’s effective weight, while submerged edges retain the water seal.
Centre Guide Gas Holder Interactive Calculator
Explore bell mass, diameter and a change in stored gas volume. The rigid bell and its guide sleeve rise and fall together. Calculate ideal gauge pressure, circular area, travel for the entered volume change, and equivalent water head.
Equation Used
- Free bell with constant effective mass and negligible guide friction; counterweights and water buoyancy are omitted.
- Circular effective area approximated by πD²/4, neglecting the central guide sleeve area.
- Volume change is at holder conditions; no gas temperature or standard-volume conversion.
- Water density 1000 kg/m³; pressure and head conversions use g = 9.81 m/s².
- Fixed tank levels are schematic; real level changes, skirt immersion and capacity are not calculated.
- A large calculated pressure or travel does not imply a physically suitable gas-holder design.
Ideal free-bell pressure and volume-change calculation. The section illustrates the historical central guide and sleeve; it is not a dimensional design of a gas holder or its water seal.
A bell guided from its center
Hiscox’s historical figure 1616 identifies the holder A, fixed central guide b, sliding tube a and water tank B. The moving sleeve is attached to the bell, so it translates with the crown and skirt. Fixed gas risers open above the internal water surface; they do not have to stretch with the bell.
Adding gas increases the space beneath the bell and raises it. Withdrawing gas lets its weight lower it. In the ideal free-bell balance, gauge pressure times effective horizontal area equals the bell’s effective weight. The drawing keeps the bell rigid and the lower edges submerged throughout its illustrative cycle.
Gas pressure depresses the water surface inside relative to the atmospheric side. The shown level difference, tank depth and guide dimensions are schematic. The calculator has no tank-depth or skirt-length inputs and therefore cannot establish seal margin.
Reading the historical arrangement
This is a central-guide, water-sealed holder, distinct from an externally framed holder or a dry-seal piston holder. The defining feature is the fixed center guide and the tube moving with the bell. The illustration shows one bell and central guide; it does not describe the equipment at a particular modern site.
The calculator illustrates how effective mass, circular area and volume change relate. It does not select a holder architecture, gas service, construction material or permissible working pressure.
Pressure, travel and hydrostatic head
Let m be bell mass in tonnes and D the effective diameter in meters. Area is A = πD²/4 m². With the model’s g = 9.81 m/s², gauge pressure is p = 1000m × 9.81/A Pa, or p/100 in mbar.
For example, a mass loading of 30 kg/m² gives 30 × 9.81 = 294.3 Pa, or 2.943 mbar. Divide pressure in pascals by 100 to convert it to mbar.
A change in gas volume ΔV requires vertical travel Δz = ΔV/A if effective area stays constant. An absolute gas volume would also require the crown and reference-volume geometry, which this calculator does not have.
With water density ρ = 1000 kg/m³, pressure-equivalent head H = p/(ρg) meters. The displayed millimeter value is H × 1000. This is a hydrostatic pressure conversion, not the required total depth of a particular tank.
Numerical example
For a 46 tonne bell and diameter 14 m, A = 49π = 153.938 m². The ideal gauge pressure is 46,000 × 9.81 /153.938 = 2931.44 Pa, or 29.3144 mbar.
A volume change of 1500 m³ then corresponds to 1500/153.938 = 9.744 m of bell travel. The equivalent water head is 2931.44/9.81 = 298.82 mm.
These results do not show that an unspecified tank has enough depth or that its guide can accommodate that travel. Bell buoyancy, sleeve area, friction, relief arrangements and structural loads are outside the ideal calculation.
Limits of the simplified model
Actual effective bell weight can change with immersion, attached equipment and other loads. Guide friction can also affect pressure during motion. The calculator holds effective mass and area constant to isolate the basic pressure balance.
The animation uses separate display scales so both a small and a large calculated travel remain readable. It does not enlarge the real capacity of a fixed tank or imply that the full range of slider combinations describes practical low-pressure equipment.
Calculator questions
Why does gas volume change travel but not pressure?
At fixed effective mass and area, p = mg/A stays constant. Increasing the entered volume change increases Δz = ΔV/A. Gas compressibility, temperature and guide friction are not part of this model.
Is the displayed water head a seal-depth specification?
No. It is the pressure-equivalent difference between water levels. Actual seal design also depends on geometry, water-level variation and remaining skirt immersion, none of which is supplied here.
Why does the moving bell include a long center sleeve?
The historical drawing shows a tube attached to the holder sliding on a fixed central guide. The animation keeps that tube attached to the crown as the whole bell rises and falls.
Can the calculator identify a safe maximum storage volume?
No. The entered volume change gives an ideal travel requirement. Available travel, tank depth, guide strength and operating limits must be established independently for an actual holder.
References & Further Reading
- Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), printed page 389, figure 1616: centre-guide gas holder.
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