Manual valve opening and closing, excessive force
Consequence: the valve will be damaged if it is light, and the safety accident will be caused if it is heavy
Measures: manual valve, its handwheel or handle, is designed according to common manpower, considering the strength of sealing surface and necessary closing force. Therefore, it is not allowed to move with long lever or long wrench. Some people are used to using the wrench, should pay strict attention, do not use too much force, otherwise it is easy to damage the sealing surface, or break the handwheel and handle. Open and close the valve, the force should be stable, not impact. Some parts of high-pressure valves with impact opening and closing have considered the impact force and the general valve can not wait. For steam valve, before opening, it shall be heated in advance and condensed water shall be removed. When opening, it shall be as slow as possible to avoid water hammer. When the valve is fully opened, turn the hand wheel back a little, so that the threads are tight to avoid looseness and damage. For open stem valves, remember the valve stem position when fully open and fully closed to avoid hitting the top dead center when fully open. It is convenient to check whether it is normal when it is fully closed. If the valve office falls off, or a large sundry is embedded between the valve core seals, the valve stem position will change when the valve is fully closed. When the pipeline is used for the first time, there is a lot of dirt inside, so the valve can be slightly opened. The high-speed flow of the medium can be used to wash it away, and then it can be slightly closed (it can’t be closed quickly or violently to prevent the residual impurities from damaging the sealing surface). It can be opened again. Repeat for many times, clean the dirt, and then put into normal operation. When the valve is normally opened, there may be dirt on the sealing surface. When it is closed, the above method shall be used to wash it clean, and then it shall be formally closed. If the handwheel and handle are damaged or lost, they should be immediately matched, and can not be replaced by a flexible wrench, so as to avoid damaging the four sides of the valve stem and failing to open and close, resulting in accidents in production. For some media, when the valve is closed and cooled to shrink the valve, the operator should close it again at a proper time to keep the sealing surface free of fine seams. Otherwise, the media flows through the fine seams at a high speed and easily erodes the sealing surface. During operation, if it is found that the operation is too laborious, the reasons shall be analyzed. If the packing is too tight, it can be loosened properly. If the valve stem is skewed, the personnel shall be informed to repair it. For some valves, when they are closed, the closing parts are heated and expanded, which makes it difficult to open; if they must be opened at this time, they can loosen the bonnet thread for half a circle to eliminate the stress of the valve stem, and then move the hand wheel.
Improper installation of valves in high temperature environment
Consequence: leakage accident
Measures: for high temperature valves above 200 ℃, they are installed at normal temperature. After normal use, the temperature rises, the bolts expand with heat, and the gap increases. Therefore, they must be tightened again, which is called “hot tightening”. The operator should pay attention to this work, or leakage will occur easily.
Not timely drainage in cold weather
Measures: when the weather is cold, the water valve is closed for a long time, and the accumulated water behind the valve shall be removed. After the steam valve stops, the condensate shall also be removed. The valve bottom is like a plug, which can be opened for drainage.
Nonmetal valve, too much opening and closing force
Measures: some of the non-metallic valves are hard and brittle, and some of them are of low strength. During operation, the opening and closing force shall not be too large, especially the strong force. Also be careful not to bump objects.
Packing pressure of new valve is too tight
Measures: when the new valve is used, the packing shall not be pressed too tightly, and the degree of leakage shall not be taken as the degree, so as to prevent the valve rod from being pressed too much, accelerate the wear, and make the opening and closing difficult. The quality of valve installation directly affects the use, so it is necessary to pay attention to the direction and position of the valve, valve construction, valve protection facilities, bypass and instrument, valve packing replacement.
No operation space in installation position
Measures: the installation position of the valve must be convenient for operation; even if the installation is temporarily difficult, it is also necessary to consider the long-term work of the operator. It is better to make the hand wheel of the valve flush with the chest (generally 1.2m away from the operating floor), so that the opening and closing of the valve is more economical. The hand wheel of landing valve shall face up, and do not tilt to avoid awkward operation. The valve of the wall leaning machine and the equipment shall also leave room for the operator to stand. It is not safe to operate in the sky, especially in acid and alkali, toxic media, etc.
Valves made of impact brittle materials
Measures: the installation and construction must be careful to avoid hitting the valve made of brittle materials. Before installation, check the valve, check the specification and model, and identify whether there is any damage, especially for the valve stem. Also rotate a few times to see if it is skewed, because in the process of transportation, it is most likely to hit the skewed stem. Also remove the debris from the valve. When lifting the valve, the rope shall not be tied on the hand wheel or stem, so as to avoid damage to these parts, and it shall be tied on the flange. The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide scraps, mud sand, welding slag and other sundries. These sundries are not only easy to scratch the sealing surface of the valve, but also can block the small valve and make it invalid. When installing the screw valve, the sealing packing (hemp and lead oil or polytetrafluoroethylene raw material belt) shall be wrapped on the pipe thread, and shall not be put into the valve, so as to prevent the valve from accumulating and affecting the medium circulation. When installing the flange valve, pay attention to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with reasonable clearance, so as to avoid excessive pressure or even cracking of the valve. For brittle materials and low strength valves, special attention should be paid. For the valve to be welded with the pipe, spot welding shall be carried out first, then the closed part shall be fully opened, and then the valve shall be welded.
Post time: Nov-27-2019