Density and Bulk modulus dependency

Density and Bulk modulus dependency The density of the hydraulic fluid varies with pressure and with air content. The isentropic bulk modulus of the hydraulic fluid is defined to be:

Equation 2: Bulk modulus as a function of the fluid density

where ρ is the density [kg/m3] of the fluid (liquid/air/vapor mixture), P its pressure [Pa] and B the bulk modulus [Pa]. The subscripts s and X mean that the bulk modulus is computed at constant entropy and constant composition.

Once one of the quantities density and bulk modulus is defined, the other is also defined through Equation 2.

It is essential that values for the density and the bulk modulus are fully consistent with these formulae. The consequence of neglecting these relations is the loss of mass conservation. This can show up quite dramatically if there is cavitation.