What are the valve installation skills and construction measures

Update:20 Nov 2020

Many valves are directional, such as stop valves, throttle valves, pressure reducing valves, check valves, etc. If they are installed upside down, it will affect the use effect and life (such as throttle valves), or they will not work at all (such as Pressure reducing valve), and 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 globe 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 (due to the upward pressure of the medium). , This is the reason why the globe valve can not be reversed. Other valves also have their own characteristics.

(1)  valve installation skills

The valve installation position must be easy to operate: even if the installation is temporarily difficult, it is necessary to consider the long-term work of the operator. It is better to align the valve handwheel with the chest (usually 1.2 meters from the operating floor), so that it is easier to open and close the valve. The hand wheel of the floor valve should be upwards, not tilted, 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 operation on the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe. Do not install the gate upside down (that is, the handwheel is downward), otherwise the medium will remain in the valve cover 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. Lift check valve, ensure that its valve flap is vertical when installing, so as to be flexible in lifting. Swing check valve, ensure that 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 not inclined in all directions.

(2)   Construction work

Installation and construction must be careful, and avoid hitting valves made of brittle materials.

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

When lifting the valve, the rope should not be tied to the handwheel or valve stem to avoid damage to 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 the screw valve, the sealing packing (wire hemp plus aluminum oil or PTFE tape) should be wrapped on the pipe thread, and do not get into the valve to avoid accumulation in 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, and then the closing part should be fully opened, and then welded to death.

(3) Protective measures

Some valves also need external protection, which is heat preservation and cold preservation. Hot steam pipelines are sometimes 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 mixed with heat; where the valve is exposed, which is unfavorable to production or causes frosting, etc., 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, and plastic.

(4) Bypass and instrument

In addition to the necessary protection facilities, some valves also have bypasses and meters. A bypass is installed. 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.

(5) Packing replacement

In stock valves, some packing is not good enough, and some are not in line with the used medium, which requires replacement of packing.

Valve manufacturers 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 circle and circle should be 180 degrees apart. For the height of the packing, the room for the gland to continue to be compressed should be considered. At present, the packing chamber at the lower part of the gland should be at an appropriate depth, which 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 oil crystals below 80 degrees Celsius, and fluorine rubber resistant to various corrosive media below 150 degrees Celsius) can be used according to specific conditions. Stacked polytetrafluoroethylene 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 raw PTFE tape can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.

When pressing the seasoning, turn 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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