The internal structure of the check valve is the key to its one-way flow function. According to its structural characteristics, check valves are mainly divided into three categories: lift type, swing type and butterfly type. These different types of check valves have different structures, but the common goal is to ensure that the fluid can only flow in one direction, thereby preventing the fluid from flowing back.
1. Swing check valve
The valve disc of the swing check valve is designed in the shape of a disc, and its working principle is to rotate around the rotating axis of the valve seat channel. Because its internal channel is streamlined, the flow resistance is lower than that of the lift check valve, so it is particularly suitable for large-caliber scenes with low flow rate and little change in flow state. However, it should be noted that the swing check valve is not suitable for pulsating flow, and its sealing performance is slightly inferior to the lift type. In addition, the swing check valve can be further subdivided into three types: single-flap type, double-flap type and multi-flap type. These different types are mainly distinguished according to the valve caliber, aiming to reduce the hydraulic impact when the medium stops flowing or flows back.
(a) Single-flap swing check valve is suitable for medium-caliber, with simple design and stable performance.
(b) Double-flap swing check valve is suitable for larger diameter, such as DN≤600, and its structural characteristics can effectively cope with fluid impact.
(c) For large-diameter (DN>600) scenarios, multi-flap swing check valve is more suitable. Its ingenious design aims to reduce water hammer and avoid damage to the sealing surface.
The installation position of the swing check valve is flexible and is not restricted by the direction of the pipeline. It can adapt to horizontal, vertical or inclined pipelines. When installed on a vertical pipeline, the medium flow direction must be from bottom to top. In addition, the swing check valve does not have an advantage in small-diameter valves, but the working pressure can reach a very high level, and its nominal pressure can reach 42MPa. At the same time, its nominal diameter is also quite large, with a maximum of more than 2000mm. This valve is suitable for a variety of working media and temperature ranges, from water, steam to corrosive media, oils and medicines, etc. The medium working temperature range is between -196℃ and 800℃.
2. Lift check valve
The valve disc of the lift check valve slides along the vertical center line of the valve body. Its design is flexible and is particularly suitable for high-pressure and small-diameter situations. The valve disc can be in the shape of a spherical ball. The valve body shape of this check valve is similar to that of a stop valve, so its fluid resistance coefficient is relatively large. When the medium flows downstream, the valve disc opens by the thrust of the medium; when the medium stops flowing, the valve disc falls on the valve seat by its own weight, thereby preventing the medium from flowing back.
Lift check valves can be divided into two types: straight-through type and vertical type. The media inlet and outlet channels of the straight-through lift check valve are perpendicular to the direction of the valve seat channel. It is usually installed on horizontal pipes, especially on horizontal pipes with a nominal diameter of 50mm. This type of check valve performs well. The media inlet and outlet channels of the vertical lift check valve are in the same direction as the valve seat channel, which is suitable for installation in vertical pipes.
In general, lift check valves have better sealing than swing check valves, but the fluid resistance is also increased accordingly. Specifically, the resistance values are ranked as follows: straight-through lift check valve > vertical lift check valve > swing check valve.
3. Butterfly check valve
The disc of the butterfly check valve is uniquely designed. It rotates around the pin in the valve seat. This structure makes its installation relatively flexible. It is not only suitable for horizontal pipes, but also can be used on vertical or inclined pipelines. However, due to its structural characteristics, the sealing performance of the butterfly check valve is relatively poor, which needs to be noted in practical applications.
4. Micro-resistance slow-closing butterfly check valve
The core components of the micro-resistance slow-closing butterfly check valve include the valve body, two semicircular discs, return springs, oil storage cylinders, slow-closing small cylinder groups, and needle valves (micro-regulating valves). This check valve is suitable for a variety of media, such as clean water, sewage and seawater, and is used in drainage pipes. It can not only effectively prevent the backflow of the medium, but also significantly limit the generation of destructive water hammer, thereby ensuring the safe operation of the pipeline. However, it should be noted that this valve is not suitable for medium containing solid particles or particles with high viscosity. It is small in size, light in weight, and its structural length is only about one-third of that of the swing check valve.