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Calculation of the waterhammer or peak of overpressure for hydraulic-fluidic systems.

Hydraulic system

In every hydraulic systems, when sudden speed variations arise to the transported fluid, impulsive pressure waves are generated which propagate through the pipe submitting every passed components to additional stresses.

The trigger could be the simple closure of the valve, the starting of a pump or the intervention of a check valve.
The rate of change of speed has effect on the entity of the peak of overpressure.

To avoid the damaging of the system is necessary to sizing up correctly the pipes and the components to withstand at the impulsive stresses which happen during the phase of operation.

Data input
Fluid data.

Selection of the kind of fluid

Density of the fluid at 20°C

Wait fluid data


Bulk modulus


Pipe data.

Selection of the type of pipe

Young's module of material

Wait pipe dimensions.


Selection of pipe dimensions

Attesa caricamento elenco dimensioni tubi.

Dimensions of the chosen pipe

Øe (mm)

Øi (mm)

Length of the pipe


Characteristics of the system.

Intervention time of the valve to the bottom line:


Fluid speed in the pipe (v):


Common values for speed values.

Working pressure:


Waiting for calculation

Calculation results
Peak of overpressure (waterhammer) kg/cm2
Total peak pressure kg/cm2
Propagating speed of the shock wave (celerity) m/s
Critical period (phase time) Tf s

Maximum overpressure.
Pressure on phase time chart. In this chart is shown the trend of the peak of overpressure (Delta P) referred to the intervention time of the valves (v m/s), below the phase time (Tf) the overpressure does not increase.
The phase time varies related to the propagating speed of the shock wave which in turn is influenced also by the temperature of the pipe and of the fluid (they have effects of their elasticity modulus), in this calculation we consider 20 20°C.

To reduce the peaks is also possible to install some dampers, also called shock absorbers for waterhammer. In commerce there are of different dimensions, for bigger systems is also possible to build, in these cases they are called air box.

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