Ideas are presented on the dynamic performance characterisation of air valves. For this purpose
the dynamics of air valve (float type), air pocket and pipe system are considered. From a
parameter study and dimensional analysis, (dimensionless) dynamic air valve characteristics are
developed. Results are presented for a vacuum breaking valve and combined vacuum
breaking/air release valve, as obtained from large scale experiments at WL | Delft Hydraulics.
The tests reveal that after valve closure always some residual air remains entrapped in the system,
which is responsible for high pressure peaks. The (dimensionless) dynamic characteristics may
be used in the estimation of the pressure surges due to the air valve closure, either by quick
estimates or in numerical models, and enable the scaling to other valve sizes.