KEVOS® MAKEOS · Hydraulics
Accumulator Circuit Sizing (Pump Deficit, Gas Volume, Recharge)
Does this cylinder stroke need an accumulator to reach its speed, how big must it be, and can the pump recharge it before the next stroke?
Sizing of an accumulator to help a pump with a fast cylinder stroke: oil volume and flow for the stroke in the time wanted, what the pump supplies in that time, the deficit the accumulator must deliver, the accumulator gas volume for the precharge, minimum and maximum pressures and the polytropic exponent (as the accumulator size tool), the recharge time at pump flow against the time available, and the installed size against the size needed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cylinder bore | mm | Bore of the cylinder (cap-side area is used). |
| Stroke | mm | Stroke length. |
| Cylinders moving together | Number of cylinders that stroke at the same time. | |
| Stroke time wanted | s | Time the stroke must take. |
| Pump flow | L/min | Flow of the pump. |
| Time available to recharge | s | Time between strokes in which the pump refills the accumulator. |
| Precharge pressure | bar | Gas precharge pressure (about 90% of the minimum working pressure for bladder types). |
| Minimum working pressure | bar | Lowest pressure at which the cylinder still does its work. |
| Maximum working pressure | bar | Pressure at which the accumulator is full (relief or unloading setting). |
| Polytropic exponent (1 slow, 1.4 fast) | Exponent of the gas process: 1 for slow (isothermal), 1.4 for fast (adiabatic) discharge. | |
| Accumulator size installed or offered | L | Nominal gas volume of the accumulator considered. |
Method and formulas
- Stroke volume V = n × π D² ÷ 4 × stroke; flow needed = V ÷ t₁.
- Pump supplies Q_p t₁; deficit ΔV = V − Q_p t₁.
- Gas volume V₀ = ΔV ÷ [(P₀ ÷ P₁)^(1/n) − (P₀ ÷ P₂)^(1/n)] with absolute pressures (as the accumulator size tool).
- Recharge time = ΔV ÷ Q_p, against the time available.
- Example: the stroke needs 45.239 L/min against 30 L/min from the pump; the accumulator supplies 0.50796 L and must be at least 1.4093 L.
Limitations
- Ideal gas; real gas at high pressure needs a correction factor.
- Pressure drop in valves and lines during the fast stroke is not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size an accumulator for a fast clamp or press stroke
- Check whether a smaller pump plus accumulator will do
- Check recharge between cycles
Who it is for
- Hydraulic engineers
- Machine designers
- Maintenance engineers
What you get
- Stroke volume and flow
- Deficit and accumulator size needed
- Recharge time and installed size check
Interpreting the result
- A fast stroke discharges nearly adiabatically: sizing with n = 1 would undersize the accumulator.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 352–368. Topic reference; no source tables or recommended settings are reproduced.
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