Plastic microfluidic structures having a substantially rigid diaphragm that actuates between a relaxed state wherein the diaphragm sits against the surface of a substrate and an actuated state wherein the diaphragm is moved away from the substrate. As will be seen from the following description, the microfluidic structures formed with this diaphragm provide easy to manufacture and robust systems, as well readily made components such as valves and pumps.

The invention relates to fluid actuator for influencing the flow along a flow surface through ejection of a fluid. By means of a like fluid actuator, a continuous flow is distributed to at least two outlet openings in order to generate fluid pulses out of these outlet openings. Control of this distribution takes place inside an interaction chamber which is supplied with fluid flow via a feed line. Into this interaction chamber there merge at least two control lines via control openings to which a respective different pressure may be applied. Depending on the pressure difference at the control openings, the flow in the interaction chamber is distributed to the individual outlet openings.

The fluid acceleration pipe includes a main body having a pipe cavity and defining a central axis. The whole inner surface of the main body is exposed to the pipe cavity. The main body is formed with at least 3 spiral ribs arranged spacedly along a perimeter direction of the main body. A spiral groove is formed between any two adjacent ones of the spiral ribs. A column-shaped imaginary datum plane is defined by the most bottom portion of each spiral groove about the central axis. A projection of the most top portion of each spiral rib on the imaginary datum plane defines a spiral line. The lead angle of the spiral line is 50 to 60 degrees. The top portion of each spiral rib has a convex-arc-shaped surface, and the bottom portion of each spiral groove has a concave-arc-shaped surface.