Hi,today I have problem with bubbles.
I can't eliminate them,I change the flasks,I used ultrasonic bath.
You experienced a phenomenon called "cavitation". This is due to dirty or clogged solvent filter (picture). For assurance you can TEMPORARY remove solvent filter and run the pump. If the bubbles disappear you need to exchange the solvent filter with a new one.
What you saw was not "air" bubbles but was "gas" bubbles which is produced by solvent evaporation due to decreased pressure. Since pump pistons suck up the solvent, a vaccum build up in solvent intake place (filter) and If solvent can not pass through the filter efficiently, gas bubbles will produce.