Steps to perform to operate the press:
First drain all water, so the rubber membrane is fully down and the maximum fruit space is available. Then insert a linen sack of proper size into the tank and fill in fruit. Close the linen sack with a rope, so later no pomace is pressed out and gets into the juice. Leave a little space so you can insert the cap. Now insert ans position the cap. OK, its time to open the tap and let the water flow into the tank. In any case be careful. If water gets in too quick splashes may occur.
Increase pressure carefully. Water pressure may be able to destroy the press. You should stop if the cap-gap gets visibly bigger. Because the cap gap is covered by the rivet ring and is therefore not visible I recommend to mark the cap all around with a pencil in position. The longer you press the less juice will come. because the pores of the fabric will be clogged. This is also much depending on the type of fruit. At a certain time you need to stop adding water, otherwise something may break. But everybody needs to judge for its own. Keep in mind, that the rivet ring and cap needs to withstand a weight equivalent of about two tons at a water net pressure of 4 bars if the average diameter of the cap is assumed at 25 cm ! Depending on your net your pressure may be much higer, so be careful ! Helpful could be to add a manometer into the pressure line to determine once the maximum operation pressure.
!! Danger !! Never operate the press using compressed air, otherwise yor press may explode and may cause severe injuries.