Views: 0 Author: Site Editor Publish Time: 2023-12-29 Origin: Site
In a liquid or gas transfer system, a check valve is a critical mechanical device designed to control the direction of flow of a fluid or gas to prevent backflow or reverse flow. Let's take an in-depth look at the principle, function and common types of check valves, including lift check valves.
The principle of the check valve is very simple and effective. Its main function is to allow the medium to flow freely in one direction while preventing the medium from returning to the system if it flows in the opposite direction. Such valves can be spheres, flappers, or pistons, and are designed to open or close automatically in response to the pressure of the fluid or gas.
wafer lift check valve
The role of the check valve are: to prevent backflow of media, to prevent the pump and drive motor reversal, as well as the release of container media.
1, Check valve can prevent the medium backflow:
Check valve has only one flow direction, that is, only along the inlet direction of flow, to prevent water flow in the opposite direction. Flowing medium from the inlet side (lower side) inflow, from the outlet side (upper side) outflow. When the inlet pressure is greater than the weight of the valve flap and its flow resistance and when the valve is opened. Conversely, the media backflow when the valve is closed.
2, Check valve can prevent the pump and drive motor reversal:
Check valve is automatic, in a direction of flow of fluid pressure, valve open; fluid flow in the opposite direction, by the fluid pressure and the self-weight of the valve flap on the valve seat, thus cutting off the flow.
3, Check valve can also be used for which the pressure may rise to more than the system pressure of the auxiliary system to provide supply pipeline.
Ⅰ, Lift check valve: vertical and horizontal two kinds. The shape of the valve body of the lift check valve is the same as that of the globe valve, so it has greater fluid resistance. The valve flap slides along the vertical centre line of the valve body. When the medium is flowing, the valve flap is opened by the medium thrust, and when the medium stops flowing, the valve flap is landed on the valve seat by self hanging.
⑴Vertical lift check valve. The medium inlet and outlet channel direction and the valve seat channel direction is the same, the flow resistance is smaller than the straight-through type. Vertical lift check valve is installed in vertical pipeline.
⑵Through the lift check valve can only be installed in the horizontal pipeline. Restricted by the installation requirements, commonly used in small diameter occasions DN <50.
Ⅱ, Rotary check valve: rotary check valve valve valve flap was disc-shaped, rotating around the valve seat channel axis for rotary motion, because the valve channel into a streamlined, flow resistance is smaller than the lifting check valve, suitable for small diameter, low-pressure, large-calibre pipeline (low flow rate and flow of infrequent changes in large-diameter occasions). Sealing performance is not as good as lifting type.
⑴Rotary check valve single valve type, double valve type and more than half of the three types, these three forms are mainly by valve calibre, the purpose is to prevent the medium to stop the flow or backflow, weaken the hydraulic shock. Single-valve swing check valve is generally applicable to medium calibre occasions. Large-calibre pipeline selection of single-valve rotary check valve, in order to reduce water hammer pressure, it is best to use a slow-closing check valve can reduce the water hammer pressure. Double valve swing check valve is suitable for large and medium calibre pipelines. Clamping double-flap rotary check valve structure is small, light weight, is a fast-developing check valve; multi-flap rotary check valve is suitable for large-calibre pipelines.
⑵Rotary check valve installation position is not restricted, it can be installed in the horizontal, vertical or inclined pipeline.
Ⅲ, Butterfly check valve: straight-through type. The structure of butterfly check valve is similar to butterfly valve. Its structure is simple, the flow resistance is smaller, and the water hammer pressure is also smaller. The valve flap rotates around the pin in the valve seat of the check valve. Disc check valve structure is simple, can only be installed in the horizontal pipeline, sealing is poor.
Ⅳ, The diaphragm check valve: there are a variety of structural forms, are using the diaphragm as the opening and closing parts, due to its water hammer performance, simple structure, low cost, rapid development in recent years. But the use of diaphragm check valve temperature and pressure by the diaphragm material restrictions.
Diaphragm check valve is suitable for easy to produce water shock on the pipeline, the diaphragm can be very good to eliminate the medium against the flow of water generated by the water shock, it is generally used in low-pressure ambient temperature pipeline, especially suitable for water pipeline, the general working temperature of the medium in the -12 - 120 ℃, the working pressure of <1.6MPa, but the diaphragm check valve can be done to achieve a larger calibre, the maximum can be reached in the DN 2000mm or more! However, the diaphragm check valve can be of larger calibre, DN can reach 2000mm or more;
After deciding that your application requires a check valve, it is critical to understand the different selection criteria to ensure that it meets the application requirements. The main selection criteria for choosing the right valve are:
Connection and pipe size. It's important to understand how the valve will be mounted (most commonly a threaded connection) and make sure it fits into the system.
Material. The medium will be in contact with the valve, so it is important that it can withstand the properties of the medium and will not contaminate it.
Pressure: Ensure that the media is capable of generating cracking pressure and, if required, backflow to close the valve.
Flow rate. Ensure that the check valve is capable of allowing the required flow rate through its application.
Operating conditions. Media temperature, external temperature, maintenance schedule, and installation orientation can affect the type of check valve.
Check valves play a key role in several industries:
Water supply and drainage systems
In urban water supply and drainage systems, check valves are used to control the direction of water flow and prevent it from returning to the source or adversely affecting water quality. This is essential to maintain the hygiene and stability of drinking water and drainage systems.
Chemical Industry
The chemical industry often involves a variety of corrosive, toxic or high temperature and pressure media. The application of check valves can effectively prevent the backflow of these dangerous media in the piping system, ensuring the safety and stability of industrial production.
Oil and gas industry
In oil and gas transmission pipelines, check valves prevent the reverse flow of oil and gas in the pipeline. This is critical to maintaining the flow of oil and gas, preventing pipeline explosions and protecting associated equipment. In oil drilling, preventing backflow of fluids from the bottom of the well is also an important application for check valves.
Pharmaceutical Industry
Piping systems in the pharmaceutical industry need to maintain strict hygiene standards. Check valves ensure that drugs and chemicals are not contaminated during manufacture and delivery, preventing cross-contamination and maintaining the purity of the production system.
Power Industry
In the cooling water system of a power station, check valves prevent the backflow of cooling water to the main unit, ensuring the proper functioning of the cooling system. Similarly, in boiler feedwater systems, check valves help maintain unidirectional water flow.
Food and Beverage Industry
In food and beverage processing, check valves are used to control the flow of fluids through pipelines to ensure product hygiene and quality. Preventing the backflow of media is critical to maintaining hygiene standards in production lines.
Air Conditioning and Heating Systems
In air conditioning and heating systems, check valves ensure the unidirectional flow of cooling or heating media through the system, preventing backflow during shutdowns or in the event of system failure, maintaining system stability and efficiency.
Wastewater Treatment
In wastewater treatment, check valves are used to prevent the backflow of wastewater to the treatment plant or to a clean water source, ensuring the proper functioning of the entire treatment system.
