Absolute-pressure single-exponent ideal-gas screening

Documented Accumulator Gas-Volume Screening Calculator

Calculate the ideal precharge gas volume and gas states for one documented liquid-delivery cycle. All three pressures must be absolute and temperature-normalized for the selected calculation basis.

Absolute pressure onlySourced exponent nNot nominal product selection

Calculation / project identifier

Accumulator type/product and manufacturer sizing source

Absolute pressure unit for p0, p1 and p2

Corrected gas precharge p0 (absolute)

Minimum operating pressure p1 (absolute)

Maximum operating pressure p2 (absolute)

Pressure reference, atmospheric conversion and precharge-temperature correction source / revision

Required delivered liquid volume ΔV

Liquid-volume unit

Delivered-volume requirement and cycle source / revision

Gas process model

Documented polytropic exponent n

Exponent, charge/discharge duration and thermal-process source

Gas identity, charge temperature and gas-state source

Real-gas and manufacturer correction disposition

Selected product limits, shell/dead-volume and application safety review

Applicability gate: this is a single-exponent ideal-gas volume screen. It assumes one gas mass and p0V0^n=p1V1^n=p2V2^n for the documented states. It does not calculate temperature correction, real-gas factors, different charge/discharge exponents, dead volume, bladder/piston limits, transient flow, heat transfer, surge/pulsation response or a catalogue nominal size.

Documented ideal-gas screening result

Ideal precharge gas volume V0

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V0 converted to litres

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Gas volume V1 at minimum pressure

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Gas volume V2 at maximum pressure

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Ideal oil fill V0−V1 at p1

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Ideal oil fill V0−V2 at p2

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Delivered-volume check V1−V2

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Precharge ratio p0/p1

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Implemented single-exponent model

p0,abs V0^n = p1,abs V1^n = p2,abs V2^n
V1 = V0(p0/p1)^(1/n)
V2 = V0(p0/p2)^(1/n)
ΔV = V1−V2
V0 = ΔV / [(p0/p1)^(1/n) − (p0/p2)^(1/n)]

Only ratios of pressures appear, but every pressure must be absolute. A gauge value must first be converted with a documented atmospheric/reference pressure in the same unit. The page never assumes that bar(g) equals bar(a) or that a fixed atmospheric offset is correct for every site/reference.

Process exponent and temperature

Isothermal operation uses n=1. A polytropic value, including 1.4 for a justified rapid nitrogen idealization, must be entered with its product/cycle source. This page does not decide n from an arbitrary time threshold and does not apply precharge-temperature or real-gas corrections.

Manufacturer reference and published example

Το HYDAC accumulator catalogue publishes the same ideal-gas equation, distinguishes isothermal/polytropic/adiabatic cases, requires temperature and real-gas corrections, and gives an example with p0=1245 psi, p1=1500 psi, p2=3000 psi, ΔV=1.35 US gal and n=1.4. The displayed equation gives V0=3.949314 US gal, reproducing the catalogue’s rounded ideal result of 3.95 US gal before its 1.16 real-gas correction and nominal-size selection. The Parker HY10-1630/US sizing guide explicitly defines its sizing pressures in PSIA, uses application/time/temperature-dependent gas coefficients and warns that temperature variation affects precharge.

Standards boundary

ISO 4413:2010, edition 3, Published and confirmed in 2021, specifies general rules and safety requirements for hydraulic systems. Its public abstract does not establish this sizing equation, exponent or precharge percentage; this page therefore does not call the arithmetic an ISO formula or claim ISO 4413 compliance. The inventory token “ISO 70” was a false positive caused by a former numeric preset beginning with 70, not a cited standard.

Why the former page was changed

The former inputs were merely labelled “bar,” inviting gauge-pressure entry into an absolute-pressure gas law. It silently chose n=1 or 1.4 from broad speed labels, published unsupported one-minute thresholds and universal 90/95% precharge rules, inserted presets/defaults and labelled the ideal V0 as the required accumulator volume without real-gas, temperature, product or reserve corrections.

Stored-energy hazard: this result is not authorization to select, charge, isolate or service an accumulator. Follow the exact manufacturer procedure and applicable law/standard. Parker’s guide states that accumulator circuits should automatically unload stored pressure when machinery shuts down. Verify rated pressure/temperature, compatible gas and elastomers, isolation, relief, discharge control, inspection and trained-personnel requirements.