In the l = 3/m = 9 Uragan-3M (U-3M) torsatron (R0 = 1 m, ā≈0.12 m, Bϕ = 0.72 T, ι(ā)/2π≈0.4), an open helical divertor is realized. A hydrogen plasma with e≈2×1018 m-3, Te≈0.3 keV, Ti≈0.1 keV is produced and heated by RF fields (ω≈ωci). The flows of diverted plasma are detected by 78 plane Langmuir probes aligned poloidally in the spacings between the helical coils in two geometrically symmetric poloidal cross-sections of the torus. In measurements of the distributions of ambipolar (e.g. the ion saturation current Is) and non-ambipolar (e.g. the current to a grounded probe Ip) plasma flows, a strong vertical asymmetry of these distributions is observed, its main characteristics being a many-fold difference in the values of Is in the outgoing flows in the upper and lower parts of the torus and the opposite signs of Ip in these flows, with the positive current corresponding to the larger ambipolar flow of the diverted plasma. Reversal of the direction of the toroidal magnetic field results in the reversal of the asymmetry, with the larger flux (and Ip>0) always flowing in the ion B×∇B drift direction. On this basis, it is concluded that the asymmetry is related to direct (non-diffusive) losses of charged particles from the confinement volume. This conclusion is validated by numerical modelling of thermal and fast particle orbits in U-3M, where qualitative agreement has been revealed between the calculated distribution of the angular co-ordinates of lost particles and the measured poloidal distributions of the flows of diverted plasma.