ValveCheck, Inc.’s 3300 Series plastic check valves are a positive seal at low back pressure design that offers excellent repeatability and dependability. They are offered in a light crack pressure that is designed to cover a wide range of air and fluid applications. These valves are constructed of nylon, polypropylene or Kynar and feature a positive ball O-ring seal made of Viton, EPDM or silicone. Maximum pressure is 125 psi; crack pressure is 1/2 psi. http://www.valvecheckinc.com/3300-series.cfm, (651) 330-3437
