A simplified model is derived for simulating gas blowdown through a thin and long tube connecting a high-pressure gas-filled reservoir to a vacuum vessel. During the depressurization process, the flow is assumed to be quasi-steady and approximated as one-dimensional. The transient compressible flow can therefore be solved analytically. The model accounts for gas nonideality and heat transfer with the ambient in both reservoirs, and for wall friction in the pipe, An experimental study has been carried out using helium and deuterium in order to validate this simplified approach. The discharge of the pressure vessel being quite rapid (a few seconds long), the measurements reliability and the required adjustments are discussed. The model predictions are shown to be in good agreement with our experimental results.