Classification of check valves and how to choose them

A valve in which the closing element opens or closes on its own due to the flow of the medium and external force, in order to prevent backflow of the medium, is called a check valve. Check valves belong to the category of automatic valves and are mainly used in pipelines where fluid flows in one direction only; they allow fluid to flow in a single direction to prevent accidents. Structure of a one-way valve: One-way valves can be classified, based on their structure, into lift-type one-way valves, swing-type one-way valves, and butterfly-type one-way valves. Lifting check valves can be divided into vertical and horizontal types. Swing check valves are divided into three types: single-disc, double-disc, and multi-disc. The butterfly check valve is of the straight-through type; the aforementioned check valves can be connected in three ways: threaded connection, flange connection, and welding. Selection of check valves: 1. Check valves are generally suitable for clean media and should not be used in media containing solid particles or having high viscosity. 2. For low-pressure check valves with a diameter of DN50mm or less, butterfly check valves, vertical lift check valves, and diaphragm check valves are suitable choices ； For medium and low pressure check valves in the DN200-DN1200 range, wear-free spherical upper check valves are recommended ； For low-pressure check valves with diameters ranging from DN 50 to DN2000, butterfly check valves and diaphragm check valves are suitable choices. 3. Diaphragm check valves are suitable for pipelines prone to water hammer; the diaphragm effectively eliminates the water hammer that occurs when the fluid flows in reverse. However, due to limitations related to temperature and pressure, they are generally used in low-pressure, normal-temperature pipelines. 4. For pipelines where the water hammer impact is relatively small or non-existent when shutdown is required, slow-closing swing check valves and slow-closing butterfly check valves are advisable. Common faults of check valves and their solutions: 1. Destruction of the valve disc. 2. Backflow of the fluid, which leads to the destruction of the valve disc. The reason for this is that the pressures of the fluid on both sides of the check valve are in equilibrium and exert opposing forces on each other; as a result, the valve disc constantly impacts against the valve seat, and valve discs made of brittle materials such as cast iron or brass get damaged. The preventive measure is to use check valves with valve discs made of ductile materials. The reasons for medium backflow are: 1. Damage to the sealing surface ； 2. Inclusion of impurities. Repairing the sealing surface and cleaning away impurities can prevent backflow. Installation of check valves: 1. Do not allow the check valve to bear any weight within the pipeline; large check valves should be supported separately so as to remain unaffected by the pressures generated by the piping system. 2. During installation, ensure that the direction of medium flow is consistent with the arrow indicated on the valve body. 3. Lift-type vertical flap check valves should be installed on vertical pipes. 4. Lift-type horizontal flap check valves should be installed on horizontal pipes.