Process Description of Dissolved Air Flotation
May 15,2023Read More
In the process of using check valves, the medium flows in the direction of the arrow shown in the diagram. When the medium flows in the designated direction, the valve disc is opened by the force of the medium. When the medium flows backward, the valve disc and seat sealing surfaces are tightly closed due to the weight of the valve disc and the reverse force of the medium, achieving the purpose of preventing medium backflow. The sealing surfaces of the check valve body and valve disc are made of stainless steel overlay. The function of check valves is to prevent medium backflow in industrial pipelines. The valve is used as a valve for cutting off boiler feedwater and steam, and it has the comprehensive functions of lifting check valves, globe valves or angle valves.
Vertical lifting check valves and bottom valves are generally installed on vertical pipelines where the medium flows from bottom to top. Pay special attention to the direction of medium flow, ensuring that the normal flow direction of the medium is consistent with the direction indicated by the arrow on the valve body. Otherwise, the normal flow of the medium will be cut off. Check valves belong to automatic valves. Their main function is to prevent medium backflow, prevent pump and motor reverse rotation, and can be used on pipelines that provide auxiliary systems that may have pressures higher than the system pressure.
Check valves can be divided into three types according to their structure: lifting check valves, rotary check valves, and butterfly check valves. Lifting check valves can be divided into vertical and horizontal types. Rotary check valves are divided into single-disc, double-disc, and multi-disc types. Medium backflow in check valves can cause the impeller of the pump to reverse, which may cause the pump to burn out. When the check valve is fully open, fluid pressure is hardly obstructed, so the pressure drop through the valve is relatively small. The valve disc of the lifting check valve is on the sealing surface of the valve seat on the valve body. The valve disc can move up and down freely, and the rest of the parts are the same as globe valves. The top of the valve disc and the bottom of the valve cover are processed with guide sleeves. The valve disc guide sleeve can move up and down freely in the guide sleeve of the valve body. When the medium flows in the forward direction, the valve disc is opened by the medium thrust. When the medium stops flowing, the valve disc falls on the valve seat by its own weight, preventing medium backflow. When the medium backflows under the action of gravity, the check valve slowly closes, effectively avoiding the water hammer caused by the sudden closing of ordinary check valves. When the centrifugal pump is opened, it is opened step by step from slow to fast to ensure that the pump is started at low load. When the pump suddenly stops working, it is closed step by step from fast to slow.
In the process of using check valves, various failures will appear. In general, the consciousness and the components of the valve parts are related, and the more components, the more failures. The main reason for medium backflow in industrial check valves is that the check mechanism is not flexible or damaged; the sealing surface is damaged or aged, and the sealing surface has not been closed for a long time, and adheres to dirt and cannot be well sealed. The methods to solve the problem of check valve medium backflow mainly include the following:
Regular cleaning, avoid using media with high viscosity and high content of abrasive particles, and check the processing quality of parts
Correct installation or assembly, and the valve cover should be in the center without being skewed
The clearance between the valve disc shaft and the guide sleeve should be moderate, taking into account the influence of temperature changes and abrasive particle invasion on the valve disc lifting, regularly inspecting, overhauling, and replacing
Select the correct sealing surface material, regularly inspect and replace rubber sealing surfaces; for media with more impurities, a filter or sewage pipe should be installed before the valve. When every aspect of the work is done well, the faults of the valve will be greatly reduced.
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