Thanks for your selection of WEKE's globe valve. As a type of pressure equipment, valve has potential hazards of pressure and creation of explosive atmosphere resulting from leakage of process fluid. For the safety purpose, user shall read this instruction to know what Weke has already taken into account in our design and manufacture, and what action shall be taken by user according to essential health and safety requirements of European Directive 2014/68/UE(PED).
When a valve is suddenly closed, shock waves are generated and cause damage to valves due to the high pressure caused by the mass of flowing water, which is so-called positive water hammer. On the contrary, when a closed valve is suddenly opened, it will also produce water hammer, called negative water hammer that is also destructive but is not as much as the former.Water Hammer Although water hammer makes a lot of noise, the real damage is caused by mechanical failure. Because the kinetic energy is converted rapidly into static pressure in pipeline, water hammer can cause pipe to break or damage pipe supports and pipe joints. For valves, water hammer can produce vibration through valve core, which may lead to failure of valve core, gasket or packing. For valves, the way to prevent water hammer is to prevent any sudden pressure change in the system, including slowing down the closing speed of the valve itself or providing a greater degree of tension and rigidity when the closure element approaches the valve seat. To prevent pressure fluctuation, the closing speed of the valve should change evenly. In some cases, when the quick open characteristic is used, it may be required to change the former to an equal percentage characteristic. Because control valves must be used for throttling flow when approaching the seat, actuators with enough thrust output should be used (e.g. pneumatic piston actuators or hydraulic actuators), which may prevent water hammer. Water hammer can also be reduced with a pressure relief valve or a buffer bucket. In addition, gas can be injected into the system, which can reduce the density of the fluid.
To understand how to deal with valve leakage, first know why this happens. To keep the valve airtight, it must have a good seal. If there is something wrong with the seal, valve leakage will occur. A ValveAs a control component in the fluid delivery system, the valve has the functions of cut-off, regulation, diversion, backflow prevention, pressure stabilization, pressure relief, etc. It is an indispensable control element for many industrial and mining enterprises. Once the valve fails, especially the leakage occurs, it will not only affect the stable operation of industrial and mining equipment, but even do harm to the environment and cause immeasurable economic and social losses to the society. Learn to identify and prevent the common leakage fault of valves. Generally speaking, the common leakage fault of valves includes two types, namely stuffing box leakage and closure member leakage.
In the daily use of valves, various failures often occur. The leakage of valves is the most common one among many failures and it generally includes internal leakage and external leakage. So, what is the difference between the two? The internal leakage of the valve usually refers to the condition that the medium still leaks from the passageway of the valve when the valve is completely closed. Generally speaking, the internal leakage means that the valve is not tightly closed and the seal is not good. This failure is usually caused by erosion and wear of media. Even if the valve lead screw (the valve stem) is screwed, the medium can still flow through the valve passage because there is still a gap between the valve core and the valve body. Generally, the external leakage of the valve is that the leakage of the medium occurs in the external seal element of valve packing after the valve is fully opened or closed. The medium leakage is caused by the poor seal between the valve and the connecting flange or connecting thread, the poor seal between the valve stem and the packing gland, sand holes on the valve body blank, or the wear of the valve body due to the medium erosion.
Gate valves can be tightly closed depending on the medium pressure, thus achieving non-leakage. When the valve is opened and closed, the sealing surfaces of the disc and the seat always contact and rub against each other, so the sealing surfaces are easy to wear. When the gate valve is about to close, the difference between the upstream pressure and downstream pressure is very large, which makes the sealing surfaces wear more seriously.