[Function] Flat,non-patterned side is the inlet.Raised,patterned side is the outlet.You can blow to the check valve,the port where the gas can be blown is the inlet. [Features] The pipe port of the check valve is designed with a -shaped card slot, non-slip and non-toxic, with good airtightness and good adsorption performance.The non-return check valve is easy to install, convenient for you to unscrew and replace [Application]- Check valve is used in fluid system to prevent reverse fluid, or used in pneumatic system to prevent reverse of compressed , can be applied to automotive parts, machinery industry, household appliances, agriculture, etc. [Material]- way check valves are sturdy, wear-resistant and durable for long-term Opening pressure: less than equal 0.5 Kpa Maximum back pressure: greater than equal 300Kpa colour:White Material:PVDF size: Diameter: 1/4 inch / 6mm, length: 1.5 inch / 38 mm Package Contents: 8 x Check Valves Only the above package content, other products are not included. Note: Light and different displays may the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.