A counterweighted gas holder stores gas beneath an inverted bell whose skirt remains immersed in a water tank. Fixed pulleys connect the bell to counterweights. As the bell rises, the weights descend by the same distance. The remaining downward load determines the ideal gauge pressure over the bell area.
Counter-weighted Gas Holder Interactive Calculator
Compare bell mass, diameter and target gauge pressure in a two-counterweight static balance. The animation shows the connected cables and submerged bell skirt. If the bell is too light, the results show zero counterweight and the ballast deficit.
Equation Used
- Circular bell area, uniform gauge pressure and g = 9.81 m/s².
- Two identical counterweights with 1:1 fixed-pulley reeving.
- Quasi-static balance; no acceleration, guide friction or cable weight.
- Effective bell mass is treated as constant; changing buoyancy is not calculated.
- Displayed motion, tank depth and water levels are schematic; no flow, capacity or containment rating is calculated.
Ideal static balance only. Enter effective bell mass for the position being considered. Buoyancy changes with immersion; cable mass, pulley friction and guide forces are omitted. The drawn tank is not dimensioned for the selected pressure.
Bell, cables and water seal
Gas occupies the space beneath the bell roof and above the internal water surface. The open lower rim stays submerged. In the illustration, the fixed inlet and outlet pipes terminate above the internal water level, while the bell moves around them.
Each cable follows a vertical tangent, the upper half of a fixed pulley, and a second vertical tangent down to a weight. Constant cable length makes the bell and weight move equal distances in opposite directions. The pulley stands are fixed to the tank foundation.
The animation illustrates storage motion. It does not derive fill speed or tank capacity from the three pressure-balance inputs.
Low-pressure storage principle
Historical water-sealed holders buffered a gas supply while their moving bells changed the enclosed volume. Counterweights reduced the effective bell load and therefore reduced the pressure required to support it.
This page explains that mechanical balance. It does not specify a gas installation, certify pressure containment or compare operating ratings of modern storage systems.
Counterweight or ballast
For a circular bell, area A = πD²/4. Gauge pressure p requires a residual downward mass M_res = pA/g. Convert mbar to pascals by multiplying by 100.
If bell mass exceeds that residual mass, each of two equal counterweights is (M_bell − M_res)/2. If bell mass is smaller, counterweights cannot help: their calculated mass is zero and the difference is reported as required ballast. The result never represents a negative physical counterweight.
Use effective bell mass for the chosen immersion. The simple calculation treats that value as constant. Actual buoyancy and cable effects can change the pressure through travel.
Example: a bell that needs ballast
An 18,000 kg effective bell mass and 12 m diameter give an area of about 113.10 m² and a bell-only pressure of 15.61 mbar. A 20 mbar target requires about 23,058 kg residual mass.
The model therefore gives zero counterweight on each side and about 5,058 kg added ballast. A heavier bell can instead require positive counterweights. This is an ideal force balance, not a recommendation to modify an installed holder.
Where the simple balance stops
As a bell moves, the amount of metal immersed in water changes. Historical holders used compensation arrangements to address this effect. Guide loads, cable mass, pulley friction and acceleration also influence an actual assembly.
The water-level difference is drawn schematically. Tank depth, skirt length, guide travel, structural stresses, gas compatibility and pressure-control equipment are outside this calculator. Input limits are exploration ranges rather than allowable operating limits.
Counterweighted-holder questions
Why do the weights move down when the bell rises?
Both ends share a constant-length cable passing over a fixed pulley. One vertical leg shortens as the other lengthens.
Why can the counterweight result be zero?
If the bell is already lighter than the residual load needed for the target pressure, counterweights would lower the pressure further. The calculator reports ballast instead.
Does the drawing set the required water-seal depth?
No. Its dimensions are schematic. The pressure balance alone does not size a tank or establish containment.
Is pressure constant through actual travel?
Not necessarily. Changing immersion changes buoyancy, and cable and guide effects can matter. The model neglects those changes.
Related actuator design tools
The bell in this model moves under gas pressure and gravity; the calculator does not select an actuator for it. For a separate actuator-driven linkage, calculate the force at the actuator pins across the full travel, including changing leverage and friction.
For a separate actuator application, check the mounting loads and pinch points, and define the control response to a jam or power loss.
The review should include the load direction, the bracket spacing, and the point in the travel where the linkage has the least mechanical advantage. If the actuator is selected from only an average force value, the design can pass an early spreadsheet check and still fail in the real assembly.
- Calculate actuator force at the worst bracket angle, not just at mid-stroke.
- Check stroke, retracted length, and extended length against the mechanism envelope.
- Confirm the structure can accept the higher loads created by a stronger actuator.
For a FIRGELLI actuator application, run the FIRGELLI actuator force calculator, then compare available stroke, force, and mounting envelope in the FIRGELLI linear actuator range. If the goal is to replace an existing unit, use the linear actuator replacement finder before assuming the new actuator is a direct fit.
References
Hiscox, Mechanical Movements, Powers, Devices and Appliances, figure 1617, printed page 389.
Accum, Description of the Process of Manufacturing Coal Gas, 1819, gas-holder and counterpoise discussion.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
