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Valve installation, maintenance and operation

Valve installation, maintenance and operation

  • Categories:Industry News
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  • Time of issue:2021-10-28
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(Summary description)After the valve is selected correctly, it must be installed, maintained and operated correctly so that its effectiveness can be fully utilized.

Valve installation, maintenance and operation

(Summary description)After the valve is selected correctly, it must be installed, maintained and operated correctly so that its effectiveness can be fully utilized.

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2021-10-28
  • Views:0
Information

After the valve is selected correctly, it must be installed, maintained and operated correctly so that its effectiveness can be fully utilized.

Section 1 Installation: The quality of valve installation directly affects the use, so careful attention must be paid.

一) Direction and location

Reverse installation will affect the use effect and life (such as throttle valve), or it will not work at all (such as pressure reducing valve), or even cause danger (such as check valve). Generally, valves have direction 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 shut-off valve is asymmetrical left and right. The fluid must pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), and the opening is labor-saving (because the medium pressure is upward). . This is the reason why the globe valve cannot be reversed. Other valves also have their own characteristics.

The valve installation position must be convenient for operation; even if the installation is temporarily difficult, it is necessary to consider the long-term work of the operator. It is best to keep the valve handwheel flush with the chest (usually 1.2 meters away from the operating floor), so that it is easier to open and close the valve. The handwheel of the floor valve should be upwards, do not tilt, so as to avoid awkward operation. The valve of the wall machine and the equipment should also leave room for the operator to stand. It is necessary to avoid operating from 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, which will easily corrode the valve stem, and it is contraindicated by certain process requirements. At the same time, it is extremely inconvenient to replace the packing.

Ming stem gate valve, do not install underground, otherwise the exposed stem will be corroded due to moisture.

Lifting check valve, make sure its valve flap is vertical when installing, so that it can be lifted flexibly.

Swing check valve, make sure its pin shaft is level when installing, so that it can swing flexibly.

The pressure reducing valve should be installed upright on a horizontal pipe, and should not be tilted in all directions.

Valve construction work

The installation and construction must be careful and avoid hitting the valve made of brittle materials.

Before installation, check the valve, check the specifications and models, and identify whether there is any damage, especially the valve stem. Rotate it a few times to see if it is skewed, because the valve stem is most likely to be skewed during transportation. Also remove the debris in the valve.

When the valve is lifted, the rope should not be tied to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange.

The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide filings, mud sand, welding slag and other debris. These debris are not only easy to scratch the sealing surface of the valve, the large particles of debris (such as welding slag) can also block the small valve and make it invalid.

When installing a screw valve, seal packing (line hemp plus lead oil or PTFE tape) should be wrapped on the pipe thread, and do not get into the valve, so as to avoid the accumulation of the valve and affect the flow of the medium.

When installing the flange valve, pay attention to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure or even cracking of the valve. Special attention should be paid to valves with brittle materials and low strength.

Valves that must be welded to the pipe should be spot welded first, then the closing part should be fully opened, and then welded to death.

Valve protection facility

Some valves also need external protection, which is heat preservation and cold preservation. Sometimes heat tracing steam pipelines are added in the insulation layer. What kind of valve should be kept warm or cold depends on the production requirements. In principle, if the medium in the valve reduces the temperature too much, it will affect the production efficiency or freeze the valve, it needs to be kept warm, or even heat; where the valve is exposed, which is unfavorable to production or causes frost and other undesirable phenomena, it needs to be kept cold. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cold insulation materials include cork, perlite, foam, plastics, etc. Water and steam valves that have not been used for a long time must be drained of stagnant water.

Valve bypass and instrument

Some valves, in addition to the necessary protection facilities, also have bypasses and meters. A bypass is installed to facilitate the maintenance of the trap. For other valves, bypasses are also installed. Whether to install the bypass depends on the valve condition, importance and production requirements.

valve packing replacement

Inventory valves, some packing is not good enough, and some are inconsistent with the used medium, so the packing needs to be replaced.

The valve manufacturer cannot consider the use of various types of different media. The stuffing box is always filled with ordinary packing, but when using it, the packing must be compatible with the medium.

When replacing the packing, press it in circle by circle. The seam of each circle should be 45 degrees, and the seams of the circle and circle should be staggered by 180 degrees. The height of the packing should consider the room for the gland to continue to be compacted. At present, the packing chamber at the lower part of the gland should be at an appropriate depth. This depth can generally be 10-20% of the total depth of the packing chamber.

For demanding valves, the seam angle is 30 degrees. The seams between the circles are staggered by 120 degrees.

In addition to the above fillers, three rubber O-rings (natural rubber resistant to weak alkalis 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 be used according to specific conditions. Stacked PTFE ring (resistant to strong corrosive media below 200 degrees Celsius) and nylon bowl-shaped ring (resistant to ammonia and alkali below 120 degrees Celsius) and other forming fillers. Outside the ordinary asbestos packing, a layer of PTFE raw material tape can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.

When compressing the packing, rotate the valve stem at the same time to keep the surrounding uniform and prevent it from being too dead. Tighten the gland with even force and not tilt.

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