This contribution presents a mixing process and device which does not contain any moving parts touching the mixing liquid. The process called hydraulic mixing is carried on in a hydraulic mixer which utilizes alternate changes of pressure in a unit caused by adequate in- and out-flows of a gas. The idea of hydraulic mixer (HM) was born during the HAZOP analysis applied at the initial step of the process design. Therefore, the drawn down concept of inherently safer HM was built in laboratory and it led to experimental verification. The performed set of experiments varied in volume of mixed liquid, dimension of device and location of dye injection. The obtained results have shown a feasibility of mixing liquid in the apparatus in which local values of Reynolds number are generally in the laminar regime but if it goes to turbulent (i.e. in the clearance and inner compartment) never reach 11,000. During the carried out experiments various physical phenomena have been observed, such as waving and formation concave–convex structures at liquid interface. Although, hydrodynamic description of the hydraulic mixing with use of modified Reynolds number has been proposed, the description and explanation of obtained results pose difficulties, raised many still open questions and provide challenges for future work.