High-pressure check valves mainly include swing type, lift type, axial flow type, etc. The following is how they work:
Swing high-pressure check valve
Opening process: When the medium enters the valve body according to the specified flow direction, the pressure of the medium acts on the valve disc, generating a force that causes the valve disc to rotate around the rotating axis. When this force is greater than the weight of the valve disc itself and other resistances such as spring force that may exist, the valve disc will rotate around the rotating axis and gradually open, allowing the medium to pass through the valve smoothly and enter the downstream pipeline.
Closing process: When the medium stops flowing or backflow occurs, the valve disc will rotate around the rotating axis in the closing direction under the action of its own gravity, spring force and the pressure of the backflow medium until the valve disc fits tightly with the valve seat, thereby preventing the medium from backflowing. In order to reduce water hammer, some swing check valves will adopt a multi-flap design, and the coordinated action of multiple valve discs will make the valve closing process smoother.
Lifting high-pressure check valve
Opening process: When the medium flows downstream, the upper part of the valve disc and the lower part of the valve cover are processed with guide sleeves, and the valve disc guide cylinder can be freely lifted and lowered in the valve cover guide cylinder. The pressure of the medium acts on the valve disc, overcoming the gravity of the valve disc and the possible spring force, so that the valve disc slides upward along the vertical center line of the valve body, opens the valve, and allows the medium to pass.
Closing process: When the medium stops flowing or reverses, the valve disc falls on the valve seat by its own weight to prevent the medium from flowing back. In some high-pressure and small-diameter lifting check valves, the valve disc can be made of a ball, and the gravity of the ball and the medium pressure are used to open and close the valve.
Axial flow high-pressure check valve
Opening process: The fluid medium enters from the inner section a1 at an average speed v1, and the cross-sectional area of the valve flow channel steadily decreases to the valve seat diameter section a2. According to the Venturi tube principle, as the flow channel diameter decreases, the medium flow rate through the valve remains constant, so the flow rate is bound to increase. At section a2, the fluid velocity increases to v2. When the flow channel cross section is further reduced to the absolute minimum cross section a3 of the valve, the velocity increases to v3. As the fluid velocity increases, the static pressure head on each cross section decreases, resulting in a static pressure difference, that is, the static pressure at the valve body cross section a3 is less than the static pressure at the valve body cross section a1. The existence of the static pressure difference provides a partial force acting on the valve disc, and the combined force of this force and the impact of the fluid on the valve disc opens the valve.
Closing process: When the medium flow rate decreases significantly, the static pressure difference decreases accordingly, allowing the spring force to overcome the fluid pressure, and the valve disc responds instantaneously and closes the valve. The light valve disc and the spring action and short axial stroke can ensure a fast self-buffering response. The rapid response and return of the valve disc can avoid fluid backflow and valve slamming, thereby eliminating the danger of pressure shock waves and the impact of water hammer.