Not sure if you have an FX pump? The easiest way to tell is to look at the base / footplate on your pump.
The following are all examples of the FX (or ‘swedish’ pump):
Not sure if you have a 3 stage or 4 stage FX pump? The easiest way to find out is to look at the top of your pump.
Only the 4 stage pump has the brass knob on the handle: