Hi Scottyee,

And for the benefit of others, there are a few differences between a volume pedal and an expression pedal. First a volume pedal is designed to sit in-line of the signal path from the output of the instrument to the input on the amplifier. It varies the signal level delivered to the amplifier.
An expression pedal is designed to connect to an expression pedal socket on the back of a keyboard or other instrument and vary the volume of the instrument (or parts of the instrument if it is capable of designating the expression controller to parts) before it is delivered to the outputs of the instrument, or it's internal amplifier and speaker setup where available.

The pedal you have Scottyee is an inline volume pedal. There are two varieties of FV50; L or H. As the names suggest one is for Low impedance signals (such as keyboards and other line level devices) whilst the H model is for high impedance signals (such as electric guitars.)

The later FV500L and H model can both be used as an expression pedal, as it has a suitable connector for this purpose, and an in-line volume pedal.

Some expression pedal models such as the EV5 or EV7 from Roland/Boss have a knob on them for setting a minimum volume level too. This restricts the active area of the sweep in the pedal, so that you never make the setting too low.

The Yamaha FC7 is an expression pedal.

My history with expression pedals really comes from using Yamaha Electone organs since the 70's. These would vary the overall master volume output of the whole instrument. I now however use an EV5 occasionally, but (when using it with a G70) get a lot from initial touch, particulalry when using dynamic arranger also. This reduces significantly the need for an expression pedal. As has been mentioned, earlier examples such as those on an Electone were designed to give the player dynamic control where none was available from the action. Touch sensitive keys only became available on affordable Electones from the FC/FE/FS/FX series of the early 80's. Certainly early Hammond organs did not have touch sensitivity either.