Optimizer tube always had air bubble

For 3 days we are facing OP starvation, the distributor engineer found that there always air bubble inside OP tube. They already replaced electrovalve and butterfly valve, also take out the bubble, but seems air bubble keep appear inside. HP engineer came yesterday, but didn't help much. Is there alternative action to maintain air bubble free of OP tube? Or may be simplest way to detect and take out air bubble from tube?

Thx, Rensi

If there are bubbles in the system this will be the steps to follow: • Check if there is a broken bag in the intermedia tank.

• Look for possible leaks in the ink system

• Purge with ink the OP line and look in all joins and valves at the ink system if you can see any bubble to identify where they are coming from.

• Replace the affected part or reconnect the affected join.