The axial check valve is widely used in oil and gas collection because of its smooth operation, small flow resistance, small water hammer pressure, good flow state, fast response to medium pressure changes, small size, low noise and good sealing. Pump outlets such as pump networks, fire-fighting and petrochemical pipelines are used as check-off devices. The axial check valve can be divided into a sleeve shape, a disc shape and a ring disc shape according to the form of the valve flap structure (Fig. 1). The sleeve-shaped structure valve flap is light in weight, sensitive in action, short in stroke, short in structure length, low pressure seal and low pressure open, closed without impact, no noise, and the spring is not directly in contact with the medium, so the service life is long, and the disadvantage is that there are two The sealing pair adds difficulty to processing, grinding and maintenance, and has a certain pressure loss. The sleeve-shaped structure is generally used for large-diameter pipeline media outlets such as long-distance pipelines or air compressor outlets, and can be installed horizontally or vertically. The disc-shaped structure has the characteristics of sensitive action, short stroke, no impact, no noise, small fluid resistance, rapid response, and only one sealing surface is convenient to manufacture, and is generally used for low-noise, no-leakage natural gas transmission, petrochemical, Medium and small diameter pipeline systems such as power plants. The ring-shaped disc valve stroke is very short, and the spring load acts to make it close quickly. Therefore, it is more conducive to reducing the water hammer pressure. The disadvantage is that the structure is more complicated and the flow resistance is larger, which is generally used for vertical pipelines. According to different working conditions, choose the appropriate structural form. The opening and closing of the flap is determined by the pressure difference between the inlet end and the outlet end of the valve. The flap opens when the medium pressure at the inlet end is greater than the sum of the medium pressure at the outlet end and the spring force. However, the degree of opening is determined by the magnitude of the differential pressure, and the valve flap is in a dynamic force balancing system. When the sum of the outlet end pressure and the spring force is greater than the inlet end pressure difference, the flap is closed and remains closed. It has good valve support and guidance to ensure that the valve flap can be well centered with the valve seat in any installation position. There is no jamming on the opening and closing, the operation is reliable, and the sealing pair is always in a good state of force and sealing. In order to ensure the circulation efficiency of the medium and reduce the loss of pressure, the valve body and the seat ring should adopt a streamlined design suitable for the flow of the medium. The front surface of the flap is designed as an arc-shaped streamline, and the tail of the valve body frame is designed as a cone-shaped flap. Different methods are used to calculate the opening height of the flap, ie the valve structure. Streamlined channel, low flow resistance, small water hammer pressure, good flow regime, low valve travel, theoretical opening height of cone seal valve is steel, guide sleeve material is stainless steel or copper alloy. The spring is a relatively important component of the axial check valve. First, the spring must ensure that the valve is opened at a low pressure. Second, the valve can be quickly closed when the valve is retracted at any position. According to this principle, the spring is selected as a compression spring in the design, wherein the spring has the smallest amount of compression when the valve flap is in the closed position and the maximum compression amount in the maximum open position. The differential pressure is the main factor in keeping the valve closed, while the spring is only attached with a small return force. According to the above principle, the valve must meet the conditions when it is opened at low pressure. When the disc is retracted at any position, the valve can be quickly closed. The spring force must be equal to or greater than the minimum 1 of the seat and the cross-sectional area at the diameter. For different forms of noise, energy saving and environmental protection. Taking the disc-shaped valve flap structure as an example, the design method is introduced. The axial check valve body is a casting, and the inner cavity passage should fully satisfy the overcurrent capability and the streamlined design to reduce the pressure loss. For thin-walled plastic materials, the wall thickness is calculated according to the fourth strength theory. Generally, the wall thickness of the valve body is determined according to the design specified standard, and the minimum wall thickness of the valve is determined, and then checked by the formula in the standard. For large-diameter high-pressure valves, reinforcing ribs are generally provided at the valve seat and flange areas to increase the rigidity of the valve body, prevent deformation of the valve seat, and add lifting lugs and feet to facilitate lifting and installation. In order to ensure the valve flow, the valve seat minimum diameter DT is 0. 85DN. In addition to meeting the strength requirements, the valve surface should be designed in a circular arc-shaped flow pattern to reduce flow resistance. The front and rear support of the axial check valve flap and the valve shaft structure for the large diameter valve, in order to ensure a good centering of the valve flap during opening and closing, a guide shaft is arranged at both ends of the valve flap, and cooperates with the guide sleeve. Ensure that the seal pair is always in a good state of force and anastomosis, while running smoothly, no jamming The differential pressure is the main factor in keeping the axial check valve closed, while the spring is only attached with a small return force. According to the above principle, the valve must meet the conditions when it is opened at low pressure. When the disc is retracted at any position, the valve can be closed quickly and the spring force must meet the conditions. At the same time, the smoothness of the flow channel should be ensured, and the tail of the fluid guide body is also designed to be conical, which ensures the flow area of the medium, reduces the pressure loss, and makes the flow state stable and without cavitation. In the axial flow check, the differential pressure is the main factor in keeping the axial check valve closed, and the spring is only attached with a small return force. This feature makes the elastic yellow of the spring yellow very small, and the reflection of the yellow is very sensitive. The valve flap can give the valve flap force when the fluid starts to flow backward, so that the valve flap can quickly react back to the seat, ensuring the valve has a longer use. Life is not damaged. At the same time, the pre-compression spring is used to form an internal pre-tightening force, which plays a role in regulating the change of the fluid. It can slow down the opening and closing speed of the valve, so as to eliminate or reduce the water hammer phenomenon caused by the closing too fast, reduce the noise and form a silent effect.