Hydraulics

Accumulator Sizing

Sizes a gas-charged hydraulic accumulator — computes cylinder volume and the pre-charge/working-pressure volume multiplier under isothermal or adiabatic conditions.

Inputs

Full-bore, full-stroke displacement

Results

Cylinder volume

—

in³

—gal
—L

Volume multiplier

—

dimensionless

Adiabatic

Accumulator volume

—

in³

—gal
—L

Accumulator sizing equation

VolAccum = Volcyl × (Pressmin / PressPre-charge)1/n 1 − (Pressmin / Pressmax)1/n
Volcyl = π (d/2)² L n = polytropic constant n = 1  → isothermal n = 1.4  → adiabatic
Isothermal (n = 1) Gas temperature stays constant — perfect heat transfer with surroundings; the shell and oil act as a giant heat sink. Applies to very slow cycles (many minutes to hours), long-term energy storage, or whenever the accumulator has ample time to exchange heat.
Adiabatic (n = 1.4) No heat transfer at all — the process is so fast the gas can't exchange heat with the shell or oil. Applies to fast cycles: emergency strokes, shock absorption, pump pulsation damping, and most actuator backup functions (under 1–3 minutes, often just seconds).