Hydraulic Accumulator Usable Oil Volume

ScopeBy the gas law, dV = V0[(P0/P1)^(1/n) - (P0/P2)^(1/n)] with absolute pressures, n = 1 isothermal (slow) or 1.4 adiabatic (fast). A 1-gallon accumulator precharged to 1,500 psig, working 1,600-3,000 psig, gives 0.44 gal usable on a slow cycle (43.6% of the shell) but only 0.34 gal run fast, since the heated gas stores less. The precharge must sit at or below the minimum working pressure (a common rule is 0.9 P1); widen the band or precharge closer to the minimum for more. A precharge set cold rises with the gas temperature (absolute-temperature ratio), so enter both temperatures when they differ: 1,300 psig charged at 70 F reads 1,474 psig at 140 F. Real-gas effects and response time are separate. A design aid; Machinery Handbook / NFPA and the accumulator maker govern.

Formula or tableP = P_gauge + 14.7; dV = V0[(P0/P1)^(1/n) - (P0/P2)^(1/n)]; n = 1 isothermal, 1.4 adiabatic. Precharge P0 <= min working P1.

Source and editionThe gas-charged hydraulic accumulator usable-volume relation with absolute pressures (Machinery's Handbook; NFPA fluid-power practice; Boyle's law, isothermal n = 1 / adiabatic n = 1.4), by name.

Free accessThe accumulator gas-law relation is standard published fluid-power design; the accumulator size, precharge, and working pressures are the user's inputs.

What governsEstimate. AHJ and licensed professional govern.

API field namesaccumulator_size_gal, precharge_psig, min_pressure_psig, max_pressure_psig, gas_process, usable_volume_gal, utilization_pct

• Gas law dV = V0[(P0/P1)^(1/n) - (P0/P2)^(1/n)], absolute pressures, n = 1 or 1.4Boyle's law / fluid-power design
• Precharge P0 at or below the minimum working pressure (common rule 0.9 P1)accumulator practice
• Scope usable volume only; precharge temperature correction, real-gas, response time are separatescope of this tile