The 11DN-01000-A-2SX part from H. S. Marston is a dual operated, 2-stage, double ended non-return valve. It is designed for use in low and medium pressure systems, providing an efficient and reliable means of controlling the flow of either gaseous or liquid mediums. The two-stage operation enables a high-flow capacity at lower valve pressures, while the double ended design ensures better performance at higher pressures. The valve is made of steel and is available in sizes ranging from 1/2" to 2". It is suitable for use in a variety of industries, including oil, gas, chemical, water, wastewater, and power.