Abstract: Granted that the gravity is the main driving force responsible for the phase separation, a mathematical model for the estimation of the settling time would be possibly established from the analysis of the velocity distribution. If the thickness of emulsion wedge turns to be negligible and the settling time obtained from the given model is equal or more than the coalescence time of droplets described by Smith and Davies, a designing processed in this way seems justified. Based upon the established model, a true settler with a horizontal area of top shape and shellow depth based on the mathematical model has been designed and used with success in practice.