Non-metallic sealed cast iron plunger valve U41SM16Z is used in petroleum, chemical, fertilizer and other long-distance pipeline systems, most of the time is used outdoors and often normally open, so that a long section of the light thread stem is exposed, causing wind and sand erosion, easy to damage, and the dark stem plunger valve stem is always in the valve, protecting the valve stem does not increase the height of the valve, installed in a small place is extremely advantageous.