This work presents an improved model of operation of downhole pump used as a boundary condition of the Damped Wave Equationproposed by Gibbs (1963). The described model predicts the main operating conditions of a pump, for example, complete or partial pump fillage, gas interference and unanchored tubing. The validation of the new model, as a boundary condition, was made by the visual comparison between predicted dynamometer cards and measured dynamometer cards (obtained in the Supervisory System for Oil Wells – SISAL, in Portuguese). The input data for obtaining the predicted cards were also collected in SISAL. A total of 18 vertical wells from the Potiguar Basin was collected. The results of the new model, as a boundary condition, were coherent with the measured cards. The predicted downhole cards were able to represent the main operating conditions of a pump. The predicted surface cards had a good approximation in relation to the measures, but the model needs some other physical phenomena to provide the attenuation of the vibrations of loads.