(1) Direction and position
Many valves are directional, such as shut-off valves, throttle valves, pressure-reducing valves, check valves, etc., if installed backwards, it will affect the use effect and life (such as throttle valve), or will not work at all (such as Pressure reducing valve), even causing danger (such as check valve). In general valves, there is a direction sign on the valve body; if there is no, it should be correctly identified according to the working principle of the valve. The valve cavity of the shut-off valve is asymmetrical, and the fluid should be allowed to 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 why the shut-off valve is irreversible. Other valves also have their own characteristics.
The installation position of the valve must be easy to operate: even if the installation is temporarily difficult, it must be considered for the operator's long-term work. It is best to align the valve handwheel with the chest (generally 1.2 meters from the operating floor), so that opening and closing the valve is more labor-saving. The handwheel of the floor valve should be facing upward, not tilting, so as to avoid awkward operation. The valve of the wall machine and the equipment should also leave room for the operator to stand. Avoid operating in the sky, especially acid and alkali, toxic media, etc., otherwise it is very unsafe. Do not install the gate upside down (ie 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 taboo for some process requirements. It is extremely inconvenient to replace the packing at the same time. Do not install the open stem gate valve underground, otherwise the exposed stem will be corroded due to moisture. The check valve of the lift type must be installed to ensure that the valve flap is vertical, so that the lift can be flexible. Swing check valve, to ensure that the pin shaft is horizontal during installation, so that the swing is flexible. The pressure reducing valve should be installed upright on the horizontal pipeline, and should not be inclined in all directions.
(2) Construction work
Installation and construction must be careful, and avoid hitting the valve made of brittle materials.
Before installation, the valve should be inspected, the specifications and models should be checked, and any damage should be identified, especially for the valve stem. It is necessary to turn it a few times to see if it is skewed, because the valve stem is most likely to be knocked during transportation. Also remove debris from the valve.
When the valve is lifted, the rope should not be tied to the handwheel or the stem, so as not to damage 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 blow off iron oxide chips, mud, welding slag and other debris. These debris are not only easy to scratch the sealing surface of the valve. Among them, 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 raw material tape) should be wrapped on the pipe thread. Do not get into the valve, otherwise the valve will accumulate and affect the medium circulation.
When installing the flange valve, 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 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.
(3) Protection measures
Some valves also need external protection, which is heat preservation and cold preservation. Hot steam lines are sometimes added to the insulation. What kind of valve should be insulated or kept cold depends on the production requirements.
In principle, when the temperature of the medium in the valve is too low, it will affect the production efficiency or freeze the valve, so you need to keep it warm or even mix the heat. Thermal 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 instrument
In addition to the necessary protection facilities, some valves also have bypasses and instruments. Bypass installed. Facilitate the maintenance of traps. Other valves are also installed with bypass. Whether to install a bypass depends on the valve status, importance and production requirements.
E) Replacement of rubber pad
In stock valves, some of the rubber pads are not good enough (beyond the shelf life), and some of them are inconsistent with the medium used, so you need to replace the rubber pads.
Valve manufacturers cannot consider the use of thousands of different media in different units. The configuration of rubber pads will be mainly universal, but the rubber pads must be adapted to the media when used.
According to the actual situation, rubber O-rings (natural rubber resistant to weak bases below 60 degrees Celsius, nitrile rubber resistant to oil crystals below 80 degrees Celsius, and fluororubber resistant to various corrosive media below 150 degrees Celsius) are used in three pieces Type PTFE ring (resistance to strong corrosion media below 200 degrees Celsius) nylon bowl ring (resistance to ammonia and alkali at 120 degrees Celsius) and other shaped fillers. Outside the ordinary asbestos packing, covered with 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 maintain uniformity around and prevent too dead, tighten the gland evenly, not tilted.