Bear in mind the diagrams shown above just illustrate the principle of operation, they are not intended to be the actual gun layout as the piston diameter would be much larger. Now if the "Velair" piston is 32 mm in diameter then the tank diameter would need to be much larger again to provide a reasonable compression ratio. Most concentric barrel pneumatic guns have a 40 mm diameter tank tube, hence a concentric inner barrel and tank would not leave much annular room for a tank volume with the inner barrel being at 32 mm diameter. That means the tank has to be placed somewhere else or any concentric tank is connected to extra side tanks in the gun. In the "Dreamair" there are side tanks either side of the internal barrel that the big piston slides in, however as the stroke of the piston is related to the spear propulsion length by the ratio of the inner and outer winding drums not all of the inner barrel is swept. That leaves about half of the inner barrel volume to serve as a tank in that gun.
The last set of diagrams show the pneumatic system reversed in the gun when compared with the original Russian/Ukrainian version from the garpun website. That allows the use of the cable and pulley system commonly seen on inverted rollerguns, the band battery being replaced by the pneumatic system. As with the inverted roller band guns the spear propulsion length is double the stroke of the energy storage system and the gearing is thus fixed at 2, unlike the "Dreamair" where the winding drum diameters control the gearing which provides some flexibility in designing the gun as to its internal drive system. For example the first alloy "Dreamair" prototype guns had no side tanks, the number of turns of the winding drum axle unwound different cable lengths for the outer cable wishbone and the inner cable connected to the sliding piston.
Ultimately the devil is in the detail, so it will be interesting to learn how the "Velair" arranges its internal components to accommodate the demands of compression ratio, start pressure and spear propulsion length in the gun.