Full port valves, also known as full bore valves, have no restriction of flow from the original pipe diameter.
That means the full port valve will maintain a consistent flow rate.
The full port design reduces cavitation (the formation of empty space) and pressure drop.
If you look at the picture, on the right, you'll see a DuraChoice full port stainless steel ball valve.
Full port valves are recommended for pipes where both solids and liquids will be flowing through the valve. The open design reduces the amount of build-up which could affect the valve’s performance over time.
Do you see a difference between the two valves?
Notice that the pipe diameter of the full port valve (right) does not decrease as you look through it. Compare that to the standard port valve on the left, which is also made by DuraChoice.
You can see the interior diameter is smaller for a valve with the same connection size. Standard port valves cost less and usually come in the same or lower pressure ratings as full port valves. They can be just as effective in some applications where full flow is not required.
The smaller opening, though, can cause pressure drop and create cavitation (the formation of empty space) causing wear on the valve.
Before making the final decision for your project, you'll want to assess your budget, the type of material you are needing, the type of material that will actually pass through the valve, and whether a consistent flow rate is absolutely needed.