The casting of light alloy components is a technology commonly used in aeronautic industry. This operation is possible, for example, using a low-pressure casting system, where it is important to control the temperature but also the maximum value and the time history of the pressure inside the furnace. For this reason it becomes important to study the pressurization circuit. In this paper a theoretical and experimental study of the pressurization circuit of a low-pressure casting furnace is presented, to individuate the temporal behaviour of the pressure inside the furnace. Particular attention has been paid to the experimental characterisation of the proportional valve with current-driven electro-pneumatic pilot. The opening of the principal valve is a function of the current of the pilot-valve. The characteristics, in terms of flow coefficients and response time, have been evaluated as a function of the upstream pressure and of the pilot current. A lumped parameters model has been developed, in which it is possible to vary the following parameters: type of valve and its coefficients, volume and temperature of the furnace, size of connecting pipes and supply pressure. The resistive and capacitive effects have been considered for the tube model but the inductive effect has been neglected. For the furnace only the capacitive effect has been take into account. The influence of the different parameters on the furnace pressure has been evaluated; experimental results obtained from tests on single components have used to find the parameters of the numerical model. The validation of the whole pressurizing furnace circuit model has been made with an experimental set-up properly realised. For every working condition, a good agreement between numerical and experimental time history of the pressure inside the furnace has been obtained. A further model validation has been made by using experimental results obtained by an existing foundry circuit. Also in this case good agreement has been obtained.