Before we get into figuring out a pump vacuum, let's look at the different pumps. In our example, we will look at Suntec pumps; all others work the same way. Suntec has many pumps, but we will examine just a few, both new and old. A fuel pump will work as a one-pipe or two-pipe system. Installing a two-pipe system will provide you with more lift (a higher vacuum) if needed. There are also one-stage and two-stage fuel pumps.

A single-stage pump will have one set of gears to pump oil from the tank to the oil burner, and if a two-pipe fuel system, the same gear set will return oil to the tank.
A single-stage pump can be operated in a one pipe or two pipe oil system, as long as we include a bypass plug when needed. Most manufacturers require it when using a two-pipe application. The advantage of piping a single-stage pump in a two-pipe application is that it is less costly than a two-stage pump and will operate at a higher vacuum than a single-stage one-pipe system. The vacuum will be less than that of a two-stage pump.
There are also 2-stage pumps, which will pump oil to the burner with one set of gears and return oil to the tank with a second set of gears. A two-stage pump should always be piped using a two-pipe system. If piped with a single pipe, it will produce about the same vacuum as a single-stage one-pipe system. We will only discuss the Suntec Mini pumps here, as they are the most common residential fuel pumps. If you have a different fuel pump, use the manufacturer's information for that type.

A good rule of thumb calculation is as follows: