Precision flow restrictors and check valves used in aerospace flight controls, landing gear and fuels systems are among the applications where design engineers need to 'push back the boundaries' in their efforts to pack small low-weight components into ever tighter space envelopes. Lee Products is a bit a specialist in this area. The company's check valve is claimed to be the smallest insert check valve available anywhere in the world, with one model measuring just 3mm diameter by just over 13mm in length.Lee's check valves are offered in three basic configurations: 4.75mm and 6.35mm diameter axial flow ball-type (204bar) screened or unscreened, forward and reverse flowing; 4.75mm diameter (forward flow/272bar) and 8.71mm diameter (reverse flow/340bar) with side-exit ports and enhanced silt resistance, and a 4.75mm diameter zero-leak, poppet-style, axial flow design, screened or unscreened, for forward and reverse flow (204bar).