This is a model of a bladder accumulator containing an ideal gas. The gas is separated from the oil. Gas compression and expansion are modeled by the equation below:



where

p		:	Gas pressure
V		:	Gas volume
		:	Polytropic index. The value for nitrogen, 1.404, has been used as the default value.
		:	Preload pressure
		:	Maximum gas volume

When the hydraulic pressure is higher than the preload pressure, the fluid starts compressing the gas bladder:



where

		:	Gas volume change
		:	Mass flow rate
		:	Fluid density

Implementation

A laminar restriction models the accumulator opening. The conductance of the restriction is put to zero when system pressure is lower than the preload pressure.

Limitations

• Gas compression and expansion processes are considered to be reversible adiabatic.
• The compressibility of the oil inside the accumulator is neglected compared to that of the gas.

Reference

C. Nordling and J. Österman, Physics Handbook for Science and Engineering, 7th ed., Lund, Sweden: Studentlitteratur, 2004 p. 32 and 190.

medium	Value: Oil() Type: Medium Description: Medium in the component
V0	Value: 0.001 Type: Volume (m³) Description: Maximum fluid volume
p0	Value: 10000000.0 Type: Pressure (Pa) Description: Preload pressure
G	Value: 1e-08 Type: ConductanceOfLaminarResistance (m³/(s⋅Pa)) Description: Conductance of laminar resistance
eventScaling	Value: 1000000.0 Type: Real Description: Parameter used to scale down variables so that events are triggered correctly
gamma	Value: 1.404 Type: Real Description: Polytropic index of gas, default value 1.404 for nitrogen gas