Hydraulic Accumulator Sizing Calculator (Bladder, Piston and Diaphragm)

What this tool does

An accumulator stores oil by compressing a nitrogen cushion, and the gas law (P₁V₁ᵏ = P₂V₂ᵏ) says how much oil comes out as the pressure falls. Use absolute pressures — the calculator adds atmospheric pressure to the gauge values you enter. A fast discharge in a second or two is nearly adiabatic (k = 1.4); a slow one leaves time for heat to flow in, which is isothermal (k = 1) and gives more oil for the same size. Precharge is usually set at roughly 80–90 % of the lowest working pressure, and a ratio of highest working pressure to precharge beyond about 4:1 is hard on a bladder.

Formula

V₀ = ΔV ÷ [ (P₀/P₁)^(1/k) − (P₀/P₂)^(1/k) ] (absolute pressures; k = 1.4 fast, 1 slow)

Variables

Worked example

Limitations

• For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
• The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.