The axial flow check valve was developed in 1930. Its development is inspired by close to the ideal design requirements: a check valve can be used to meet the large reliability of different applications and small maintenance operating costs. After many years of application, axial flow check valves have proven their reliability and ability to withstand a wide range of operating conditions and are used in many demanding applications. The flow surface of the valve body surface of the axial flow check valve, the flow guide cover, the valve flap, etc. should have a streamline shape, and the front circle is pointed. The fluid is mainly laminar on its surface with little or no turbulence. In addition to the function of the general check valve, the axial flow check valve is also designed with a shock absorbing spring. The combined sealing seat structure of the hard seal with soft seal has anti-sounding and shock absorbing effects, which is convenient for on-site maintenance. The unique axial flow shuttle structure has the advantages of small flow resistance, large flow coefficient and small size. It is the preferred valve for oil and gas gathering pipeline network system at home and abroad, especially for the export of oil pump. It is suitable for oil, gas, water slurry and pipeline systems containing H2S+C02 acid corrosive medium, and controls the medium to flow countercurrently. The axial flow check valve adopts an axial flow shuttle structure, and the valve flap is provided with a buffer damping spring. When the medium flows downstream, the valve flap opens, the medium flows through the axial flow passage of the valve body, and the medium is pushed open. When the valve flap is used, the spring acts as a buffer to avoid the impact vibration between the valve flap and the valve body when the ordinary check valve is opened. When the medium flows in the opposite direction, the valve flap closes quickly, and the valve flap fits snugly against the valve seat, preventing the medium from flowing backward. The combined hard seal with soft seal seat structure can effectively reduce the impact noise when the valve flap and the valve seat are attached. This kind of check valve is an ideal product for preventing the reverse flow of the fluid and eliminating noise and vibration. (1) Axial flow check valve type The axial flow check valve can be divided into a sleeve shape, a disc shape, a ring disc shape and the like according to the form of the valve flap structure. The basic structural form is shown in Fig. 6-41 to Fig. 6-43. (2) Structural characteristics 1There is a shock absorbing spring designed to avoid the vibration and noise generated by the direct impact between the valve flap and the valve body when the ordinary check valve is opened. 2The valve seat adopts the combined sealing structure with hard seal and soft seal, which has the effect of noise reduction and shock absorption, which is convenient for users to carry out on-site inspection. 3 compact structure, beautiful appearance and small size. 4 unique axial flow shuttle structure with small flow resistance and large flow coefficient. Diaphragm check valves are a type of check valve that has developed rapidly in recent years. Although the operating temperature and working pressure of the diaphragm type check valve are limited by the diaphragm material, it prevents the water hammer from being good in performance, simple in manufacture, low in cost, and low in noise, and is particularly suitable for applications where pressure and temperature are low. Diaphragm check valves are available in a variety of configurations. (3) Working principle of axial flow check valve The opening and closing of the flap is determined by the pressure difference between the inlet end and the outlet end of the valve. When the inlet end pressure is greater than the sum of the outlet end pressure and the spring force, the flap opens. As long as there is a pressure difference, the valve flap is always open, but the degree of opening is determined by the magnitude of the pressure difference. When the sum of the outlet end pressure and the spring force is greater than the inlet end pressure, the flap is closed and remains closed. Since the opening and closing of the valve flap is in a dynamic force balance system, the valve runs smoothly, without noise, and the water hammer phenomenon is greatly reduced. If the fluid flow rate pressure does not support the valve at a large opening and remains in a stable open position, the flap and associated moving parts may be in a state of constant vibration. In order to avoid premature wear, noise or vibration of moving parts, the diameter of the check valve is selected according to the fluid state. The valve flap of the axial flow check valve is light in weight, which can reduce the friction on the guide surface and return to the seat quickly. The low mass, low inertia flap passes through a short stroke and contacts the seat surface with minimal impact. This will reduce the damage to the sealing surface of the seat and prevent the seat from leaking. The axial flow check valve is closed quickly, and there is no impact. The valve with low mass and low inertia contacts the valve seat surface with a short stroke and with a small impact force, which can keep the sealing surface of the valve seat in good condition and avoid damage. More importantly, it can greatly reduce the formation of pressure fluctuations and ensure system safety.