ISO 10767-1:2015 establishes a test procedure for measuring the source flow ripple and source impedance of positive-displacement hydraulic pumps. It is applicable to all types of positive-displacement pumps operating under steady-state conditions, irrespective of size, provided that the pumping frequency is in the range from 50 Hz to 400Hz.

Source flow ripple causes fluid borne vibration (pressure ripple) and then airborne noise from hydraulic systems. This procedure covers a frequency range and pressure range that have been found to cause many circuits to emit airborne noise which presents a major difficulty in design of hydraulic fluid power systems. Once the source flow ripple and source impedance of hydraulic fluid power pump are known, the pressure ripple generated by the pump in the fluid power system can be calculated by computer simulation using the known ripple propagation characteristics of the system components. As such, this part of ISO 10767 allows the design of low noise fluid power systems to be realized by establishing a uniform procedure for measuring and reporting the source flow ripple and the source impedance characteristics of hydraulic fluid power pumps.

In ISO 10767-1:2015, calculation is made for blocked acoustic pressure ripple as an example of the pressure ripple. An explanation of the methodology and theoretical basis for this test procedure is given in Annex B. The test procedure is referred to here as the two pressures/two systems method. Ratings are obtained as follows:

a) source flow ripple (in the standard "Norton" model) amplitude, in cubic meter per second[m3/s], and phase, in degree, over 10 individual harmonics of pumping frequency;

b) source flow ripple (in the modified model) amplitude, in cubic meter per second [m3/s], and phase, in degree, over 10 individual harmonics of pumping frequency; and its time history wave form,

c) source impedance amplitude, in Newton second per meter to the power of five [(Ns)/m5]., and phase, in degree, over 10 individual harmonics of pumping frequency;

d) blocked acoustic pressure ripple, in MPa (1 MPa = 106 Pa) or in bar (1 bar = 105 Pa), over 10 individual harmonics of pumping frequency; and the RMS average of the pressure ripple harmonic f1 to f10.