How many types the check valve has? 

A check valve refers to a valve whose opening and closing part is disc-shaped and rely on its own weight and medium pressure to prevent the medium from flowing back. The check valve is one kind of automatic valve, is also known as one way valve, cut-off valve, return valve, isolating valve. 

The commonly used check valves are as follows: 

一．lift check valve:

the lift check valve is divided into vertical lift check valve and horizontal lift check valve. The valve body shape of the lift check valve is same as that of the globe valve, so the lift check valve’s fluid resistance is larger. The disc of the lift check valve slides along the vertical center-line of the valve body. When the medium flows downstream, the valve disc is opened by the thrust of the medium. When the medium stops flowing, the valve disc will fall back on the valve seat due to self-sinking. 

1. For the vertical lift check valve, the inlet and outlet channel of the medium are oriented in the same direction with the valve seat channel, and the lift check valve has smaller flow resistance than the straight through check valve. The vertical lift check valve can be installed in vertical pipelines. 

2. the horizontal lift check valve can be only installed in the horizontal pipelines. With the limit of the installation requirements, the horizontal lift check valve is usually used in small diameter pipelines with DN<50. 

二．Swing check valve: 

The disc of the swing check valve is disc-shaped and rotates around the axis of the valve seat channel. Because the internal channel of the valve is streamlined, the flow resistance of the swing check valve is higher than that of the lift check valve. The swing check valve has a small size, and is suitable for medium and small diameter and low pressure large diameter pipelines(low flow rate and infrequent flow change in the case of large diameter). the sealing performance of the swing check valve is not as good as the lift check valve. The installation position of the swing check valve is not limited and can be installed on horizontal and vertical or inclined pipelines. 

三. wafer butterfly type check valve: 

The wafer butterfly type check valve is one kind of straight through check valve. The structure of the wafer butterfly type check valve is similar to the butterfly valve. Its structure is simple, and the flow resistance is small, and the water hammer pressure is also small. For the check valve, the disc rotates around a pin in the seat. This disc check valve wafer type has a simple structure and can only be installed on horizontal pipelines, and its sealing performance is poor.