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Matters needing attention in common valve use
Open and close the valve, the force should be stable and not impact. Some parts of high-pressure valves that have been opened and closed due to shocks have considered such impact forces and ordinary valves cannot be equal.
For the steam valve, before opening, it should be heated in advance and the condensed water should be eliminated. When opening, it should be slowed down as much as possible to avoid water hammer.
When the valve is fully open, the handwheel should be turned upside down a little to tighten the threads tightly to avoid loose damage.
For bright-stem valves, remember the position of the stem when fully open and fully closed to avoid hitting the top dead center when fully open. And easy to check whether it is normal when fully closed. If the valve is detached, or if large debris is inserted between the valve core seals, the valve stem position will change when fully closed.
When the pipeline is used for the first time, there is a lot of internal dirt. You can slightly open the valve, use the high-speed flow of the medium to flush it away, and then close it gently (cannot be closed quickly or violently to prevent the residual impurities from pinching the sealing surface). Turn it on again, repeat this many times, rinse the dirt, and then put it back into normal work.
Normally open valve, dirt may be stuck on the sealing surface. When closing, it should be washed away by the above method, and then closed formally.
If the handwheel or handle is damaged or lost, it should be equipped immediately. It can not be replaced by a flexible wrench, so as not to damage the four sides of the valve stem, opening and closing failure, and an accident in production.
For some media, after the valve is closed, it will cool down and cause the valve to shrink. The operator should close it again at an appropriate time so that there are no crevices on the sealing surface. .
During operation, if it is found that the operation is too laborious, the cause should be analyzed. If the packing is too tight, it can be properly relaxed. If the valve stem is skewed, the personnel should be notified to repair it. Some valves, in the closed state, the closing member is thermally expanded, which makes it difficult to open; if it must be opened at this time, the valve cover screw can be loosened half a turn to one turn to eliminate the valve stem stress, and then move the handwheel.
2. Precautions for valve installation and use 1. High-temperature valves above 200 ° C are at normal temperature during installation. After normal use, the temperature rises, the bolts expand due to heat, and the gap increases. Therefore, they must be tightened again. Operators should pay attention to this work, otherwise leakage will occur easily.
2. When the weather is cold, the water valve is closed for a long time, and the water behind the valve should be removed. Condensate should also be drained after the steam valve is stopped. The bottom of the valve is like a wire plug, which can be opened to drain water.
3. Non-metallic valves, some are hard and brittle, and some have low strength. During operation, the opening and closing force cannot be too large, especially not to be vigorous. Also pay attention to avoid object collision.
4. When using the new valve, do not press the packing too tightly, so as not to leak, so as not to cause too much pressure on the valve stem, which will accelerate the wear and tear, and it will be difficult to open and close.
The quality of the valve installation directly affects the use, so careful attention must be paid to the direction and location of the valve, valve construction operations, valve protection facilities, bypass and instrumentation, and valve packing replacement.
(I) Direction and position Many valves have directional properties, such as shut-off valves, throttles, pressure reducing valves, check valves, etc. If they are installed upside down, they will affect the use effect and life (such as throttle valves), or It does not work at all (such as a pressure reducing valve) and even causes danger (such as a check valve). Ordinary valves have directional signs on the valve body; if not, they should be correctly identified according to the working principle of the valve.
The valve cavity of the globe valve is asymmetrical on the left and right. The fluid must pass through the valve port from bottom to top, so the fluid resistance is small (determined by the shape), and the opening is labor-saving (because the pressure of the medium is upward). . This is why the shut-off valve cannot be reversed. Other valves have their own characteristics.
The valve installation position must be convenient for operation; even if the installation is temporarily difficult, the long-term work of the operator must be considered. It is best to align the valve handwheel with the chest (usually 1.2 meters away from the operating floor). In this way, it is easier to open and close the valve. The handwheel of the floor-standing valve should be facing up and not tilted to avoid awkward operation. The valve of the wall-to-wall machine and the equipment should also allow the operator to stand. It is necessary to avoid operation in the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe.
Do not install the gate valve upside down (that is, the handwheel is downward), otherwise the medium will remain in the bonnet space for a long time, it is easy to corrode the valve stem, and it is forbidden for some process requirements. It is extremely inconvenient to change the packing at the same time.
Open-stem gate valves should not be installed underground, otherwise the exposed valve stem will be corroded due to humidity.
The lifting check valve should be installed vertically to ensure that it can be lifted flexibly.
For swing check valve, the pin should be level during installation to allow flexible swing.
The pressure reducing valve should be installed upright on a horizontal pipe, and it should not be inclined in all directions.
(II) Valve construction work Installation and construction must be careful not to hit the valve made of brittle materials.
Before installation, check the valve, check the specifications and models for damage, especially for the valve stem. You need to turn it a few times to see if it is skewed, because it is the easiest to bump the valve stem during transportation. Also remove debris from the valve.
When the valve is being lifted, do not tie the rope to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange.
The pipeline to which the valve is connected must be cleaned. Compressed air can be used to remove iron oxide filings, mud, sand, welding slag and other debris. These debris not only easily scratch the sealing surface of the valve, but large particles (such as welding slag) can also block small valves and make them ineffective.
When installing a screw valve, the sealing packing (linen plus lead oil or Teflon raw material tape) should be wrapped in the pipe thread, so as not to get into the valve, so as to prevent the valve from accumulating and affecting the medium flow.
When installing flange valves, pay attention to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel and the gap is reasonable to prevent the valve from generating excessive pressure or even cracking. Pay particular attention to brittle materials and low-strength valves.
Valves to be welded to the pipe should be spot welded before the closing part is fully opened and then welded to death.
(3) Valve protection facilities Some valves also need external protection facilities, which are heat preservation and cold preservation. Sometimes heat tracing steam lines are added to the insulation. What kind of valve should be insulated or kept cold depends on the production requirements. In principle, where the temperature of the medium in the valve is too low, it will affect production efficiency or freeze the valve, it will need heat preservation, or even heat tracing; where the valve is exposed, it is unfavorable to production or causes frost, and other undesirable phenomena, it needs to keep cold. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc .; cold insulation materials include cork, perlite, foam, plastic, etc.
Water and steam valves that have not been used for a long time must be drained of standing water.
(IV) Bypass and instrumentation In addition to the necessary protection facilities, there are also bypass and instrumentation valves. A bypass is installed for easy maintenance of the trap. Other valves are also equipped with bypass. Whether to install a bypass depends on the condition, importance and production requirements of the valve.
(5) Packing replacement inventory valve. Some packings are not easy to use, and some do not match the use of the medium. This requires the packing to be replaced.
Valve manufacturers cannot consider the use of thousands of different types of media. The stuffing box is always filled with ordinary packing, but when used, the packing must be adapted to the medium.
When changing the packing, press it in circles. The seams of each circle are preferably 45 degrees, and the seams of the circles are staggered 180 degrees. For the height of the packing, it is necessary to consider the room for the gland to continue to be compressed. At present, it is necessary to allow the depth of the gland to press the packing chamber to an appropriate depth. This depth can generally be 10-20% of the total depth of the packing chamber.
For demanding valves, the joint angle is 30 degrees. The seams between the circles are staggered 120 degrees.
In addition to the fillers mentioned above, three rubber O-rings (natural rubber resistant to weak bases below 60 degrees Celsius, nitrile rubber resistant to oils below 80 degrees Celsius, and fluorine rubber resistant to various corrosive media below 150 degrees Celsius) can also be used according to specific conditions. Stacked polytetrafluoroethylene ring (resistant to strong corrosion media below 200 degrees Celsius) nylon bowl ring (resistant to ammonia and alkali below 120 degrees Celsius) and other shaped fillers. The outer asbestos packing is covered with a Teflon raw material tape, which can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.
When pressing the packing, turn the valve stem at the same time to keep the surroundings even and prevent too much death. Tighten the gland tightly and not to tilt.
Editor of Shanghai Nuoyou Valve Industry Co., Ltd.