Hello,
I bought synplant recently, I write music in Sibelius and import the midi into logic but when i use these midi files with synplant the volume always jumps back to full volume is there any way to fix that?

Probably a MIDI controller #7 in the beginning of those midi files. If it is hard to remove from the midi data you could try reassigning the controller number in Synplant. Choose "Reassign MIDI Controllers" from the main menu and click and drag the little (7) symbol above the volume slider. This one: