Process equipment are usually made by assembling them from parts. The idea of this paper is to speed up the equipment design using the history of different designs, and using lists of equipment parts to make a set of mechanically sound designs. A possible set of equipment designs is combined based on the information of the parts lists. This methodology utilizes two basic advantages of computers: large memory capacity for storing knowledge from old design cases, and calculation efficiency for combining different equipment combinations. This type of an idea can be implemented as a case-based reasoning system where the case-base consists of the well documented old designs. The retrieval is done by distance functions, but the adaptation is implemented using combinatorial calculus. At first, the specification of the design problem at hand is compared to the old cases in the case-base. Process and mechanical parameter values from the nearest case's of the design problem specification as well as part of the input data are then used to identify suitable design combinations. However, the parameter values of the cases should be first adapted for the design problem. It can be done by using the scale-up or scale-down parameters to the corresponding problem. The equipment lists on the other hand are defined as different groups which describe physical parts, like motors, gears, shafts, etc. In the proposed system an equipment is pre-defined so that there should be parts from certain groups in order to create a combination. The combinations of the equipment parts are updated as the lists of parts are changed. In the proposed design system all the mechanically sound combinations are at first created. The combinations are the proposals for the solution of the process design problem. A software tool has been constructed for this kind of idea. The proposed idea can be especially useful for the equipment manufacturers in process industries. Design offices can as well utilize the proposed idea if equipment manufacturers provide them with necessary data from their equipment parts. An example of the proposed computerized tool has been implemented for the design of top-entering fluid mixers.