[Function] Flat,non-patterned side is the inlet.Raised,patterned side is the outlet.You can blow air 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 pagoda-shaped card slot, non- and non-toxic, with good airtightness and good adsorption performance.The non-return check valve is easy to install, convenient to unscrew and replace [Application]- Check valve is used in fluid system to prevent reverse flow fluid, or used in pneumatic system to prevent reverse flow of compressed air, 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 use Opening pressure: less than 0.5 Kpa Maximum back pressure: 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 cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.