The check valve, also known as the check valve, is an automatic valve. It relies on the pressure of the flowing medium in the pipeline to push the valve disc to close and open the valve. When the medium stops flowing and the check valve disc closes, it can effectively prevent the backflow of the medium in the pipeline, which plays a great role in ensuring the safety of the pipeline.

止回閥按結構劃分，可分為升降式止回閥、旋啟式止回閥和蝶式止回閥三種。升降式止回閥可分為立式和直通式兩種。旋啟式止回閥分為單瓣式、雙瓣式和多瓣式三種。蝶式止回閥分為蝶式雙瓣、蝶式單瓣，以上幾種止回閥在連接形式上可分為螺紋連接、法蘭連接、焊接和對夾式連接四種。

According to the structure, check valves can be divided into lift check valve, swing check valve and butterfly check valve. Lift check valves can be divided into vertical and straight through. Swing check valves are divided into single valve, double valve and multi valve. Butterfly check valves are divided into butterfly double valve and butterfly single valve. The above check valves can be divided into threaded connection, flange connection, welding and wafer connection.

安裝止回閥是為了保證水泵內部水流的流向，從而保障水泵的正常工作。所以關于止回閥的安裝位置，到底是安裝在水泵前還是水泵后，可以分兩種情況：

The check valve is installed to ensure the flow direction of water inside the water pump, so as to ensure the normal operation of the water pump. Therefore, the installation position of the check valve can be divided into two situations: whether it is installed in front of or behind the water pump:

一種是安裝在水泵前豎吸管端頭，也叫底閥。目的是為了不用抽一次水向水泵充一次水，因為水泵內以及泵前的吸管內無水時水泵只能空轉抽不上水，所以水泵內必須充滿水才能抽出水。這種水泵的安裝是高于液面時的一種方法，也叫負壓法。

One is installed at the end of the vertical suction pipe in front of the water pump, also known as the bottom valve. The purpose is to fill the water pump with primary water without pumping primary water, because when there is no water in the water pump and the suction pipe in front of the pump, the water pump can only idle and can not pump water, so the water pump must be filled with water to pump water. The installation of this water pump is a method above the liquid level, also known as negative pressure method.

另一種是安裝在水泵的后方。這種安裝方法是液面高于水泵的情況下，方便啟停水泵時不用關水泵出水閥，特別是對于母管制水泵系統，防止發生倒流的情況。

The other is installed behind the water pump. This installation method is convenient when the liquid level is higher than the water pump. When starting and stopping the water pump, there is no need to close the water outlet valve of the water pump, especially for the main pipe water pump system to prevent backflow.