Apologies for the long description, I hope that I understand correctly .
I'm looking for a volume pedal, which is connected between the output to the instrument and piano combo. But this pedal should be so designed that in the normal position to the maximum volume. Pressed - also the maximum.
That is the volume control starts when the foot pedal is placed (heel presses the pedal and the toe begins to control the volume).
//I saw a similar pedal in an old synthesizer Vermona about 15 years ago//
Is there such a pedal on the market today?

It's called an "expression pedal". They are available from many makers -- for example:

http://www.m-audio.com/products/en_us/EXP.html

But there is a complication you should know about:

"Synthesizers" usually include a jack (socket) for an expression pedal, but:

"digital pianos" do _not_ include that jack!

So I can't use one on my Casio PX-350.

. Charles

Charles,
1. It is not expression pedal - expr pedal connect to special input, it is volume pedal - connect between DP output and amplifier
2. I ask about pedal with normal signal if not pressed

Dunno if it's what you're after, but in my guitar rig I use a Morley Volume Plus pedal (http://www.morleypedals.com/dpvo+.html) which allows you to choose what is the minimum amount of volume it starts with. This is great for me as I use it in the amp effects loop so it means the signal is exactly the same between the instrument & amp BUT I set it so that heel down gives me about 80% volume and toe down gives 100%, so by putting heel down and turning up the amp to rhythm level, when I put the toe end down it allows me to keep the same exact tone but just play at full blast for solos so it gives that umph to cut above the other instruments.

May be wrong, but it works on electric guitars that if you put a volume pedal in line from instrument to amp, it may well change the tone/characteristic of the instrument and not just alter the volume, hence putting it in the effects loop instead as it then enters the signal AFTER the pre-amp stage and not before it.

When it comes to virtual organs people use MIDI for the Swell pedal, which, in essence, is a volume control. I don't know how straight forward it is to do that to control the volume of a DP itself, but with the organ software I use it's relatively straightforward.