Smart Products, Inc. offers Series 500 miniature check valves. Valves feature a unique tamper-resistant, one piece design and a compact size. Valves are easily mounted in-line for liquid or air applications. Spring pressure ranges from 0.07 to 20 psi. Valves can be used for liquid or air related applications, and are made of polypropylene, nylon, acrylic, acetal, PVDF, polycarbonate, Ultem®, and ABS materials.