Series of Posts on Preventing Common Problems in Instrument Installation (1)
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Series of Posts on Preventing Common Problems in Instrument Installation (Part 1): We welcome fellow enthusiasts to actively participate in the discussion of these issues. Constructive suggestions will be rewarded generously; having relevant images will earn additional points as a bonus. By gathering such problems and their solutions, we can avoid similar issues arising in future installations and create a favorable environment for maintenance work. Thank you! 1. When installing the tray supports, there are not enough brackets or hangers; the span between the trays is too large; the supports are uneven, of weak strength, not properly arranged or secure; or the fixing points are not firm enough. l Analysis and prevention: l When installing the bridge frame, hangers or supports should be installed in accordance with the following specifications: l 0.5m from each end of the bridge frame joints ； Every 1.5 to 3 meters ； turning point ； Vertical cable trays are installed every 1.5 meters. The hangers and supports should be installed vertically, neatly, firmly, without any tilting. The bolts securing the tray connection plates are tightened thoroughly without any omissions, with the nuts located on the outside of the tray. The cable tray should be installed below pipelines for flammable and explosive gases as well as thermal pipelines. There must be no less than 2 connection bolts with locknuts or lockwashers at each end of the connector pieces between the metal cable trays. The lateral deviation of the cable tray shall not exceed 50 mm ； The deviation of the cable tray’s levelness per meter should not exceed 2 mm ； The verticality deviation of the cable tray should not exceed 3 mm. The tray supports must be evenly spaced, provide uniform load distribution, appear neat and tidy, and be firmly welded. For fixing methods, brackets or hangers are chosen first, followed by supports.
2 When installing galvanized wire conduits, U-shaped clamps are not used to fix them; instead, they are directly spot-welded to the support frame. There are more than 2 bends in the wire conduit, making it difficult to pass the wires through. The length of the wire conduit was insufficient; instead of adding teeth and a wire gland, the steel pipe was simply welded to extend it, which damaged the galvanized coating that provides corrosion protection.
Another important point is that the cable trays should be firmly fixed to the supports; in many cases this step is not taken, as it is assumed that the weight of the cables will suffice to hold them in place, but such an assumption is not reliable.
3 Install pressure gauges; in any case, use condensation elbows, under the pretense that this serves as a buffering mechanism, which results in waste. When installing a pressure gauge, no gasket is used, and PTFE tape is wrapped around the threads, which causes leaks.
As a supplementary note, a expansion joint needs to be provided at regular intervals. The cable tray can be fixed to the bracket using a fixing clip, while the telescopic section is secured with a sliding clip.
When installing cable trays, it is essential to keep the trays for control cables and power distribution cables separate! If they cannot be separated, for example when placed in a cable trench, it is necessary to isolate the control circuits separately by installing a small set of metal trays within the cable trench to prevent signal interference
When selecting where to install a thermometer, it isn’t necessary to insert it at the 1/3 mark; factors such as the flow rate of the fluid and the pipe diameter must be taken into account. In areas with large pipe diameters, such as at the pump outlet, it is necessary to use thicker sleeves and reduce the depth of insertion to account for water hammer effects during startup. When installation is only possible at bends, it is again necessary to use thicker sleeves or shorten the installation length
4 Flow meter installation: For any type of flow meter, the required straight pipe section is \"10 units in front and 5 units behind.\" If the instructions are not read carefully, it’s not true that 10 units in front are always necessary; some applications can be satisfied with a shorter length, while others require more than 10 units in front.
I’ve started working at a factory, doing instrument maintenance. Almost all explosion-proof hose connectors for instrument connections never use PTFE tape, and when connecting instruments, the stripped ends of the instrument cables are never wrapped with tape.