sizing tubes ventures

[Kariush]

you have the same mambo problem: the downstream load losses will wipe out the depression in the suction zone. the fluid tends to go away through the venturi instead of "drawing" the other fluid.

Did you put any non-return valves?

no for the moment I didn't put them. You say that with those I can solve the problem?? my feeling is that of instability of the flow through the venturi, in fact this wrong effect of the venturi occurs only sometimes, inexplicably without reason.