The function of this type of valve is to allow the medium to flow in only one direction and prevent the medium from flowing in one direction. Usually, this valve works automatically. Under the action of fluid pressure flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the fluid pressure and the self weight of the valve disc act on the valve seat, so as to cut off the flow.

其中止回阀就属于这种类型的阀门，它包括旋启式止回阀和昆山良工阀门升降式止回阀。昆山良工阀门旋启式止回阀有一介铰链机构，还有一个像门一样的阀瓣自由地靠在倾斜的阀座表面上。为了确保阀瓣每次都能到达阀座面的合适位置，阀瓣设计在铰链机构，以便阀瓣具有足够有旋启空间，并使阀瓣真正的、的与阀座接触。

The check valve belongs to this type of valve, including swing check valve and Kunshan Lianggong valve lift check valve. Kunshan Lianggong valve swing check valve has a hinge mechanism, and a valve disc like a door freely rests on the inclined seat surface. In order to ensure that the valve clack can reach the appropriate position of the valve seat surface every time, the valve clack is designed in the hinge mechanism, so that the valve clack has enough swing space and makes the valve clack really and comprehensively contact with the valve seat.

瓣可以全部用金属制成，也可以在金属上镶嵌皮革、橡胶、或者采用合成覆盖面，这取决于使用性能的要求。旋启式止回阀在完全打开的状况下，流体压力几乎不受阻碍，因此通过阀门的压力降相对较小。

The flap can be made of metal, or inlaid with leather, rubber or synthetic coverage, depending on the performance requirements. When the swing check valve is fully open, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small.

\升降式止回阀的阀瓣座落位于阀体上阀座密封面上。此阀门除了阀瓣可以自由地升降之外，其余部分如同截止阀一样，流体压力使阀瓣从阀座密封面上抬起，介质回流导致阀瓣回落到阀座上，并切断流动。根据使用条件，阀瓣可以是全金属结构，也可以是在阀瓣架上镶嵌橡胶垫或橡胶环的形式。像截止阀一样，流体通过升降式止回阀的通道也是狭窄的，因此通过升降式止回阀的压力降比旋启式止回阀大些，而且旋启式止回阀的流量受到的限制很少。

\The disc seat of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except that the valve disc can rise and fall freely, the rest of the valve is like a stop valve. The fluid pressure lifts the valve disc from the sealing surface of the valve seat, and the medium backflow causes the valve disc to fall back to the valve seat and cut off the flow. According to the service conditions, the valve disc can be of all metal structure or inlaid with rubber pad or rubber ring on the valve disc frame. Like the stop valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow of the swing check valve is rarely limited.

止回阀常见故障及处理方法常见故障有：

Common faults and treatment methods of check valve include:

①阀瓣打碎

① Disc broken

②介质倒流。

② Media backflow.

引起阀瓣打碎的原因是：

The causes of disc breakage are:

止回阀前后介质压力处于接近平衡而又互相“拉锯”的状态，昆山良工阀门阀瓣经常与阀座拍打，某些脆性材料(如铸铁、黄铜等)做成的阀瓣就被打碎。预防的办法是采用阀瓣为韧性材料的止回阀。

The medium pressure before and after the check valve is close to balance and "sawing" with each other. The valve disc of Kunshan Lianggong valve often beats the valve seat, and the valve disc made of some brittle materials (such as cast iron, brass, etc.) is broken. The way to prevent is to use the check valve with the valve disc made of ductile material.

介质倒流的原因有：

The reasons for media backflow are:

①密封面破坏

① Sealing surface damage

②夹入杂质。

② Inclusion of impurities.

修复密封面和清洗杂质，就能防止倒流。

Repairing the sealing surface and cleaning impurities can prevent backflow.