There are several styles of Unist positive displacement pumps. The pump you have depends on several things including what type of fluid you are pumping and whether or not your pump is 'stacked' with other pumps. If your pump is one of several in a stack, its position in the stack determines its style. Consult the chart below (click on the image for larger view) to determine your pump style and type.
Click here for a video on our new MV (Multi-Viscosity) pumps which also has some good information on identifying all types of pumps.