For valves, not only installation and maintenance, but also operation.
I. Opening and closing of manual valves
Manual valves are the most widely used valves. Their handwheels or handles are designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, it is not possible to use a long lever or a long plate hand to move the board. Some people are accustomed to using the handwheel, should pay strict attention to, do not exert too much, or easily damage the sealing surface, or break the handwheel, handle.
Open and close the valve, force should be smooth, not impact. Some parts of high-pressure valves with impact opening and closing have considered the impact force which is not equal to that of general valves.
For steam valves, before opening, they should be pre-heated and condensate removed. When opening, they should be as slow as possible to avoid water hammer.
When the valve is fully opened, the handwheel should be reversed a little to tighten the threads so as to avoid loosening damage.
For open stem valves, remember the stem position when fully open and fully closed to avoid hitting the dead point when fully open. It is also convenient to check whether it is normal when it is totally closed. If the valve runner falls off or there is a large amount of debris embedded between the valve core seals, the position of the stem will change when the valve is fully closed.
When the pipeline is first used, there are many internal dirt, so it can open the valve slightly, flush it away by using the high-speed flow of medium, then close it gently (can not close quickly, close sharply, in order to prevent residual impurities from injuring the sealing surface), open it again, repeat so many times, flush dirt, and put it into normal work.
Often open the valve, there may be dirt sticking on the sealing surface. When closing, it should be washed clean by the above method, and then formally closed.
If the handwheel and handle are damaged or lost, they should be matched immediately, and can not be replaced by movable winding plate hand, so as to avoid damaging the four sides of the valve stem and failing to open and close, so as to cause accidents in production.
Some media, cooling after valve closing, shrink the valve, the operator should close again at an appropriate time, so that the sealing surface does not leave slits, otherwise, the medium flows through the slits at high speed, it is easy to erode the sealing surface.
When operating, if it is found that the operation is too arduous, the reasons should be analyzed. If the packing is too tight, it can be relaxed properly. If the valve stem is skewed, the repairman should be notified. Some valves, in the closed state, the closing parts are heated and expanded, which makes it difficult to open. If it must be opened at this time, the cover threads can be screwed half to one turn, eliminating the stem stress, and then the plate operates the handwheel.
II. Cautions for Valve Installation and Use
High temperature valves above 1 and 200 C must be tightened again because they are installed at normal temperature, and after normal use, the temperature rises, the bolt expands and the clearance increases, so they are called "hot tightening". Operators should pay attention to this work, otherwise they are prone to leakage.
2. When the weather is cold, the water valve closes for a long time, and the backwater behind the valve should be removed. Condensate water should also be excluded after the steam valve stops. The bottom of the valve is like a silk plug. It can be opened and drained.
3. Non-metallic valves, some hard and brittle, some low strength, when operating, opening and closing force can not be too large, especially not strong. Attention should also be paid to preventing objects from bumping.
4. When the new valve is used, the packing should not be pressed too tightly, so as not to leak out, so as to avoid too much pressure on the valve stem, accelerate wear and tear, but also hard to open and close.
Valve installation quality directly affects the use, so we must pay attention to the direction and location of the valve, valve construction, valve protection facilities, bypass and instrumentation, valve packing replacement.
(1) Direction and position
Many valves have directionality, such as globe valves, throttle valves, pressure relief valves, check valves, etc. If inverted, it will affect the service effect and life (such as throttle valves), or not work at all (such as pressure relief valves), or even cause danger (such as check valves). General valves have direction marks on the valve body; if not, they should be correctly identified according to the working principle of the valve.
The valve chamber of the globe valve is asymmetrical from left to right, so the fluid should pass through the valve mouth from bottom to top, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to medium pressure upward), and the medium does not press the packing after closing, which is convenient for maintenance. This is why the globe valve can not be reversed. Other valves also have their own characteristics.
The position of valve installation must be easy to operate; even if it is temporarily difficult to install, it should also be considered for the long-term work of operators. Best valve handwheel and chest alignment (generally 1.2 meters from the operating floor), so that the opening and closing of the valve is more labor-saving. The hand wheel of the landing valve should be upward, not inclined, in order to avoid the awkward operation. The valves of wall machine and equipment should also leave room for operators to stand. It is very unsafe to avoid elevation operation, especially acid-base, toxic medium, etc.
Gate valves should not be inverted (i.e. handwheel down), otherwise the medium will remain in the cover space for a long time, which is easy to corrode the stem, and is taboo for some process requirements. It is very inconvenient to replace fillers at the same time.
Open stem gate valve, do not install in the underground, otherwise due to humidity and corrosion exposed stem.
Lifting check valves should be installed with vertical discs so as to be flexible in lifting.
Swing check valve should be installed to ensure its pin level so as to swing flexibly.
Pressure relief valves should be installed upright in horizontal pipelines and not inclined in all directions.
(2) Valve construction
Installation and construction must be careful, do not impact the valve made of brittle materials.
Before installation, the valve should be checked to check the specifications and models, and to identify whether there is any damage, especially for the stem. Turn it a few times to see if it's skewed, because it's the most prone to bump into the skewed stem during transportation. Also remove debris from the valve.
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