A check valve should be installed on return piping if there will be a pressurized return line or the trap drains to an overhead return line (Fig. B).
如果存在一个压力回路，或者疏水阀排放口位于回路管道的上方，则应该安装一个止回阀(图b)。
2
With the valve cover tilted up you can see the single overhead CAM shaft and valves.
与阀盖倾斜了，您可以看到单一的架空凸轮轴和阀门。
3
It is equipped with asphalt return tube, anti-puffing pressure vent valve, anti-aging overhead nitrogen valve, thermometer, volumeter and output asphalt rapid discharge valve and coupling.