FF2 - Full Function Trailer Valve, Single valve system - easy to install, maintain and troubleshoot. Built-in pressure protection and anti-compounding functions: FMVSS-121 compliant, eliminates broken foundation components caused by compounding of spring brake. Space age engineering grade composites: resists corrosion, lighter and more durable than aluminum. Built-in service and spring brake quick release. Heavy wall mounting nipple is treated to resist corrosion and withstand severe duty applications. Service brake priority ensures air tank pressure is sufficient to stop vehicle when spring brakes are first released. Can be used with single or twin air tanks.