embodiment of the present invention the present flow controller includes the body 9 and stem 11 and integral diaphragm 13 which are generally cylindrical in shape not shown and which are formed of a resilient deformable material such as tetrafluroethylene resin known as teflon supplied by dupont company the inner stem 15 of cylindrical shape engages the cylindrical aperture 19 in the body 9 in interference fitting fashion i e the diameter of the inner stem 15 is larger than the diameter of the aperture 19 however since the body 9 is also formed of a resilient deformable material such as tetrafluroethylene resin e g teflon the two members conveniently slide one within the other to establish a positive fluid seal the flow controlling properties of these two members is established by a tapered groove 17 formed longitudinally within the wall of the inner stem 15 as illustrated thus fluid under pressure can pass only through the groove 17 from one side of the seal to the other and the volume of fluid under pressure per unit time that passes through the flow controller is determined by the length of the tapered groove 17 which protrudes out of aperture 19 fluid may thus flow in either direction between parts 21 and 23 with comparable precision and flow characteristics the length of groove 17 which protrudes from aperture 19 is determined by the rotation of the threaded knob insert 25 relative to the members 9 and.