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What are the installation and contraindications for valves such as gate valves and butterfly valves?

2023-11-13 15:16:29

During the installation process of gate valves, butterfly valves and other valves, the quality of the installation will directly affect the normal operation in the future, so you must pay attention to it. So, how to install gate valves and butterfly valves? 

Five key points for installing the five major valves:

1. Direction and location

Many valves are directional:

For example, stop valves, throttle valves, pressure reducing valves, check valves, etc., if installed upside down, will affect the use effect and life (such as throttle valves), or will not work at all (such as pressure reducing valves), or even Causing hazards (e.g. check valves). Generally, valves have direction marks on the valve body. If not, it should be correctly identified based on the working principle of the valve.

The valve cavity of the stop valve is asymmetrical from left to right, and the fluid must pass through the valve port from bottom to top. In this way, the fluid resistance is small (determined by the shape), and it is labor-saving to open (because the medium pressure is upward). After closing, the medium does not press the packing, which is convenient for maintenance. , this is why the stop valve cannot be installed reversely. Other valves also have their own characteristics.

The valve installation location 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 position 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-standing valve should be facing upwards and not tilted to avoid awkward operation. The valves of the wall-mounted equipment should also leave room for the operator to stand. Avoid operating with your head up, especially with acids, alkalis, toxic media, etc., otherwise it will be very unsafe.

Do not install the gate upside down (that is, with the hand wheel facing downwards), otherwise the medium will remain in the valve cover space for a long time, which will easily corrode the valve stem, and is contraindicated by certain process requirements. It is extremely inconvenient to replace the packing at the same time. Do not install rising stem gate valves underground, otherwise the exposed stem will be corroded by moisture.

When installing the lift check valve, ensure that its valve disc is vertical so that it can lift flexibly. When installing the swing check valve, ensure that its pin is level so that it can swing flexibly. The pressure reducing valve should be installed upright on a horizontal pipe and should not be tilted in any direction.

Valve installation taboos

2. Construction work

Before installation:

① Carefully check whether the models and specifications of all valves meet the design requirements. (According to the valve model and factory instructions, check whether they can be used under the required conditions, and perform water pressure or air pressure tests if necessary.)

② In addition, check whether the packing is intact, whether the gland bolts have sufficient adjustment margin, and whether the valve stem and valve disc are functioning properly and whether they are stuck or skewed. (The sealing surface of the valve disc must be closed tightly. For valves with threaded connections, the thread quality should be checked. Unqualified valves cannot be installed and should be stacked or marked separately.)

③ Clear the debris inside the valve.

Installation process:

① When lifting the valve, do not tie the rope to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange.

② The pipeline connected to the valve must be cleaned.

③ Compressed air can be used to blow away iron oxide chips, mud, sand, welding slag and other debris. Not only can these debris easily scratch the sealing surface of the valve, but large particles of debris (such as welding slag) can also block small valves and cause them to fail.

④ When installing a screw valve, the sealing packing (linen plus aluminum oil or polytetrafluoroethylene raw material tape) should be wrapped on the pipe thread and should not get into the valve to avoid accumulation in the valve and affecting the flow of the medium.

⑤ When installing flange valves, pay attention to tightening the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with a reasonable gap to prevent the valve from generating excessive pressure or even cracking. Pay special attention to brittle materials and valves with low strength. Valves that need to be welded to the pipe should be spot welded first, then the closing member should be fully opened and then welded shut.

3. Protective measures

Some valves also require external protection measures, which are insulation and cold insulation. Sometimes heating steam pipelines are added to the insulation layer. What kind of valve should be kept hot or cold depends on production requirements.

In principle, if the temperature of the medium in the valve drops too much, which will affect production efficiency or freeze the valve, it needs to be kept warm or even heated; if the valve is exposed, which is detrimental to production or causes frosting and other undesirable phenomena, it needs to be kept cold. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc.; cold insulation materials include cork, perlite, foam, plastic, etc.

4. Bypass and instrumentation

The necessary protection facilities for valves include bypass and instrumentation. A bypass is installed. Convenient for drain valve maintenance. Other valves are also equipped with bypasses. Whether to install a bypass depends on the valve condition, importance and production requirements.

Valve installation taboos

5. Packing replacement

For valves in stock, some packings no longer work, and some do not match the medium used, so the packings need to be replaced.

When replacing the packing, press it in circle by circle. The seam of each circle is preferably 45 degrees, and the circles are connected at 180 degrees. The packing height should consider the room for continued compression of the gland. At present, the lower part of the gland must press the packing chamber to an appropriate depth. This depth can generally be 10-20% of the total depth of the packing chamber. For valves with high requirements, the seam angle is 30 degrees. The seams between the circles are staggered by 120 degrees.

In addition to the above-mentioned fillers, three pieces of rubber O-rings can also be used according to specific circumstances (natural rubber is resistant to weak alkali below 60 degrees Celsius, nitrile rubber is resistant to oil crystals below 80 degrees Celsius, and fluorine rubber is resistant to various corrosive media below 150 degrees Celsius). Stacked polytetrafluoroethylene rings (resistant to strong corrosive media below 200 degrees Celsius) nylon bowl rings (resistant to ammonia and alkali below 120 degrees Celsius) and other forming fillers.

Wrapping a layer of polytetrafluoroethylene raw material tape outside ordinary asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When compressing the seasoning, turn the valve stem at the same time to keep the surroundings even and prevent it from being too tight. Tighten the gland with even force and do not tilt it.

What are the key points and taboos of valve installation?

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