Basic Effects of Fluid Properties

The effects of temperature and pressure on hydraulic system fluid properties and flow characteristics are listed below:

Density - Effects orifice and valve volume flow rates. As density increases, orifice and valve flow rates will decrease (see orifice flow equations).

a)     Increasing pressure increases density

b)     Increasing temperature decreases density

Kinematic Viscosity – Effects pipe (tube) volumetric flow rate. As viscosity increases, pipe flow rate will decrease (see orifice flow equations). Kinematic viscosity increases with increased pressure and decreasing temperature.

a)     Increasing pressure increases kinematic viscosity

b)     Increasing temperature decreases kinematic viscosity

Bulk Modulus - Effects compressibility of fluid and system response time (see pressure derivative equation). As bulk modulus decreases, the pressure derivative will decrease leading to slower response times. Compressibility will affect the performance of actuators, motors and pumps because the stiffness of the fluid is less as bulk modulus is reduced.

a)     Increasing pressure increases bulk modulus

b)     Increasing temperature decreases bulk modulus