What are the selection requirements for Forged Steel globe valves? For low pressure check valves below DN50mm, butterfly check valves, vertical lift check valves and diaphragm check valves should be selected.        止回閥是指依靠介質本身流動而自動開、閉閥瓣，用來防止介質倒流的閥門，又稱逆止閥、單向閥、逆流閥、和背壓閥。止回閥屬于一種自動閥門，其主要作用是防止介質倒流、防止泵及驅動電動機反轉，以及容器介質的泄放。止回閥還可用于給其中的壓力可能升至超過系統(tǒng)壓的輔助系統(tǒng)提供補給的管路上。止回閥主要可分為旋啟式止回閥（依重心旋轉）與升降式止回閥（沿軸線移動）。    Check valve refers to the valve that automatically opens and closes the disc depending on the flow of the medium itself to prevent medium backflow, also known as check valve, one-way valve, counterflow valve, and back pressure valve. Check valve is an automatic valve. Its main function is to prevent medium backflow, reverse pump and drive motor, and release of container medium. Check valves can also be used in pipelines to supply auxiliary systems where pressure may rise above system pressure. Check valves can be divided into swing check valves (rotating according to the center of gravity) and lift check valves (moving along the axis).        對于止回閥的選用要求，必須知道以下幾點：    For the selection requirements of check valves, the following points must be known:        對于DN50mm以下的高中壓止回閥，宜選用立式升降止回閥和直通式升降止回閥；    For high and medium pressure check valves below DN50mm, vertical lift check valves and through lift check valves should be selected.        對于DN50mm以下的低壓止回閥，宜選用蝶式止回閥、立式升降止回閥和隔膜式止回閥；    For low pressure check valves below DN50mm, butterfly check valves, vertical lift check valves and diaphragm check valves should be selected.        對于DN大于50mm、小于600mm的高中壓止回閥，宜選用旋啟式止回閥；    For high and medium pressure check valves with DN greater than 50 mm and less than 600 mm, swing check valves should be selected.        對于DN大于200mm、小于1200mm的中低壓止回閥，宜選用無磨損球形止回閥；    For medium and low pressure check valves with DN greater than 200 mm and less than 1200 mm, wear-free spherical check valves should be selected.        對于DN大于50mm、小于2000mm的低壓止回閥，伊選用蝶式止回閥和隔膜式止回閥；    For low pressure check valves with DN greater than 50 mm and less than 2000 mm, butterfly check valves and diaphragm check valves are selected.        對于要求關閉時水擊沖擊比較小或無水擊的管路，宜選用緩閉式旋啟止回閥和緩閉式蝶形止回閥。    For pipelines requiring less water hammer or no water hammer when closing, slow-closing swing check valve and slow-closing butterfly check valve should be selected.