Modelling of the growth and separation of the boundary layer has been extended from the diffuser section of Venturi scrubbers to the whole unit. Predicted pressure drops have been compared with published data over a range of system pressures. The Full Boundary Layer Model gives very good predictions of pressure loss for Pearce-Anthony Venturis at high pressure unlike other models. The sensitivity of the model to values of relevant parameters has been determined. Correct values of the initial boundary layer parameters and the effects of system pressure on them are identified.