Simulating particles & liquid in a cyclone

[JuhaHo]

I'm beginning to get some results. However here's another issue for me. Particles are much heavier than the liquid. On attached screenshot, there's a red line on the bottom, where the bottom valve of this system is located. The liquid isn't moving on the downward pipe and so, nether the particles aren't. The idea is, that particles being heavy, should go down to the valve and fill the pipe to halfway up. When that's done, the bottom valve is opened and the particles are flushed down.

Now, How can I tell tyFlow, the particles should ignore the fluid force at certain level? Not all particles would go down. Those will continue with the fluid upwards and will be removed on next phase.