Apparatus for monitoring amount and directions of fluid flow in fluid power systems

A standard fitting for permanently connecting together an appliance and a pipe in a fluid power system, the standard fitting comprising a tubular body having coupling portions at opposite ends thereof, an annulus fitted within said tubular body and carrying a rotor having blades, said tubular body and said annulus each having an opening therethrough which openings are aligned transversely of the axis of rotation of the rotor, an electrically-insulating sealing sleeve received within the pair of said aligned openings, and an electrically conductive plug fitted within said sleeve and presenting inner and outer end faces, the inner end face of said plug being triangular with one side arranged substantially parallel with the end face of each said blade of said rotor when such blade is in the vicinity of said inner end face and the outer end face of said plug being provided for temporary contact with a probe terminal of a portable unit comprising the remainder of an electrical circuit in which said rotor and said plug together constitute a cyclically variable capacitor such that as each said blade of said rotor traverses the inner end face of said plug in one direction the capacity increases from a minimum value to a cut-off at a maximum value and as each said blade of said rotor traverses the inner end face of said plug in the opposite direction the capacity decreases from a cut-in at said maximum value to said minimum value, whereby the opposite direction of rotation of said rotor may be differentiated.