Educational Use Only — This tool demonstrates Gay-Lussac's Law for rigid scuba cylinders.

Gas Law: Temperature & Pressure

How temperature changes affect pressure in a rigid scuba cylinder (Gay-Lussac's Law)

Setup

Scenario

Cylinder

Temperature

189.1 bar 4 °C
12 l
Set up your scenario, calculate p2 in your head, then click below to check your answer.
Final Pressure p2
—
Pressure Change Δp
—
Surface Gas Volume Change
—
volume at 1 bar (Δp × cylinder volume ÷ 1 bar)
Dive Time Change at 20 m
—
Surface Air Consumption 20 l/min at 3 bar (1+20/10)
Cylinder maximum working pressure: 200 bar.

Temperature Range

💡 Why Does This Happen?

Gas molecules move faster at higher temperatures and hit the cylinder walls harder, increasing pressure. Since the cylinder is rigid (constant volume), all the extra kinetic energy translates directly to higher pressure.

Practical tip: Compressors generate significant heat during filling — gas inside a freshly filled cylinder can be 40–50 °C above ambient. If you fill to 200 bar in a warm shop and dive in a cold lake, don't be surprised to see only ~180 bar on your gauge. That's not a leak — it's physics.

Rule of thumb: ~0.6 bar change per 1 °C at 200 bar working pressure.

Gay-Lussac's Law (Isochoric Process)

p1 / T1 = p2 / T2
pressure / temperature ratio is constant at constant volume (T in kelvins)
Rearranged:
p2 = p1 × T2 / T1
Accuracy and limits of this model

This sandbox intentionally uses a simple ideal-gas model to demonstrate the effect of temperature on pressure.

  • Pressure reference: Gay-Lussac's law strictly uses absolute pressure, while a cylinder gauge shows pressure above the atmosphere. Using the gauge reading directly is a small high-pressure approximation.
  • Real gas: At high cylinder pressures, air and nitrox no longer behave as ideal gases. Their compressibility depends on pressure, temperature, and composition, and can affect the result more than the pressure-reference approximation.
  • Temperature: The calculation assumes a uniform gas temperature and thermal equilibrium. A recently filled or rapidly heated cylinder can have substantial temperature gradients.
  • Cylinder and gauge: The cylinder's internal volume changes slightly with pressure and temperature, and the gauge itself has measurement uncertainty.

Fire scenario: High temperature also reduces the strength of steel and aluminium cylinders. This sandbox models only an idealized pressure change; it does not assess cylinder integrity or safety in a fire.