(1) Direction and location Many valves are directional, […]
(1) Direction and location
Many valves are directional, such as stop valves, throttle valves, pvc ball 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), or even cause danger (such as check valve). Normal valves have direction signs on the valve body; if not, they should be correctly identified according to the valve's working principle. 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 (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.
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 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 upside down (that is, the handwheel is down), 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. The exposed stem gate valve should not be installed underground, otherwise the exposed stem will be corroded due to moisture. When installing the lift check valve, make sure that its valve flap is vertical, so that it can be lifted and moved flexibly. For swing check valves, ensure that their pin shafts are level when installing, so that they can swing flexibly. The pressure reducing valve should be installed upright on a horizontal pipe, and should not be tilted in all directions.
(2) Construction work
The installation and construction must be careful, and never hit 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 hoisted, 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 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, 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 need to be welded to the pipe should be spot welded first, 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 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.
(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.
Five) Replacement of rubber pads
Inventory valves, some of the rubber pads are not good enough (exceeding the shelf life), and some do not match the medium used, so you need to replace the rubber pads.
The valve manufacturer cannot consider the use of various types of different media. The configuration of the rubber pad will be mainly of general-purpose type, but when using it, the rubber pad must be adapted to the medium.
The selection of the rubber pad can be based on the actual situation, using rubber O-rings (natural rubber resistant to weak alkalis below 60 degrees Celsius, nitrile rubber resistant to oil crystals below 80 degrees Celsius, fluoro rubber resistant to various corrosive media below 150 degrees Celsius) three-piece stack Type 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 shaped 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 pressing the rubber pad, 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.