Views: 56 Author: Site Editor Publish Time: 2023-01-06 Origin: Site
Globe Check Valve, also known as a shut-off valve, is a forced sealing valve, so when the valve is closed, pressure must be applied to the disc to force the sealing surface not to leak. When the medium enters the valve from the bottom of the disc, the resistance that the operating force needs to overcome is the friction between the valve stem and packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve. Therefore, the diameter of the valve stem must be large, otherwise, the failure of the valve stem to bend will occur. Next, let's take a look at Globe Valve's operation and moment analysis.
Here is the content list:
Operation of Globe Valve.
Globe Valve's moment analysis.
1. For Globe Valve, not only must be able to install and maintain but also be able to operate. When opening and closing the Globe Valve, the force should be smooth without impact. Some parts of the high-pressure Globe Valve with impact opening and closing have considered that the impact force cannot be equal to the general cast iron Globe Valve.
2. When the Globe Valve is fully opened, the hand wheel should be turned upside down a little to make the threads tightly to avoid loosening and damage.
3. When the pipeline is first used, there is a lot of dirt inside. You can slightly open the Globe Valve, use the high-speed flow of the medium to wash it away, and then close it gently (do not close quickly or violently to prevent residual impurities from pinching the sealing surface), turn it on again, repeat this many times, rinse off the dirt, and then put it into normal work.
4. If the Globe Valve is normally open, there may be dirt on the sealing surface. When closing the Globe Valve, use the above method to wash it clean, and then formally close it tightly. If the handwheel and handle are damaged or lost, they should be equipped immediately, and they cannot be replaced by a flexible wrench, so as not to damage the square of the valve stem, fail to open and close, and cause accidents in production.
5. Some media cool down after the cut-off valve is closed, causing the valve to shrink. The operator should close it again at an appropriate time so that there are no slits on the sealing surface. Otherwise, the medium flows through the slits at high speed and is easy to be eroded the sealing surface.
6. During operation, if the operation is found to be too strenuous, the reason should be analyzed. If the packing is too tight, it can be loosened appropriately. If the valve stem is skewed, the personnel should be notified to repair it. For some Globe Valves, when the valve is in the closed state, the closing part is heated and expands, making it difficult to open. If it must be opened at this time, the thread of the valve cover can be loosened by half a circle to one circle to relieve the stress of the valve stem, and then turn the handwheel.
When the Globe Valve starts to close from the fully open position, as the valve clack descends, the fluid creates a pressure difference between the front and rear of the valve clack to prevent the valve clack from falling, and this resistance increases rapidly as the valve clack descends. When the Globe Valve is fully closed, the pressure difference between the front and back of the disc is equal to the working pressure of the medium, and the resistance is the largest at this time. Coupled with the mandatory sealing force, the operating force at the moment the Globe Valve is closed increases rapidly. During the opening process of the valve, the thrust caused by the medium pressure or the pressure difference between the front and rear of the disc all help to open the valve. In addition, the torque at the moment of opening the valve may exceed the torque at the time of closing the valve, because at this time it is necessary to overcome a large static friction force. When the Globe Valve is opened, when the opening height of the valve clack reaches 25% to 30% of the nominal diameter of the stop valve, the flow rate has reached the maximum, which means that the Globe Valve has reached the fully open position, so the fully open position of the Globe Valve should be controlled by the valve clack. to determine the itinerary. The situation when the Globe Valve is closed and when it is closed again is similar to that of a forced sealing gate valve. Therefore, the closed position of the Globe Valve should be determined by increasing the operating torque to the specified value.
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