Two days ago, I met a customer who said that the flue expansion joint in their factory was removed during maintenance, and the tie rod was screwed to death when it was put back. As a result, within two days of turning on, the bellows directly cracked. You say it was wrong or not? The tie rod, which was meant to protect the expansion joint, turned out to be a "killer".
Therefore, in today's article "Restoration and Installation of Flue Expansion Joint", let's not talk about those theories floating in the sky, but something real-you follow these steps to ensure no mistakes.
01 Don't hurry to dismantle it first, find out what kind of expansion joint you have on your hand
Many people went into battle with wrenches and crowbars as soon as they came up, but when they were removed, they found out-huh? Why is this thing different from what I loaded last time?
There are two main types of expansion joints used in our flue: metallic and non-metallic. Inside the metal, most commonlyUniversal corrugated expansion jointAndHigh temperature axial expansion jointThey come with their own pull rods or guide tubes. Nonmetallic, that's what you saidNon-metallic expansion joint (fabric fiber expansion joint), no metal ripples, all soft connections.
How to tell quickly? See if there is a metal bellows between the flanges at both ends-yes, it is metal; No, only fabric or rubber sandwich layer, that is non-metallic. One more point: Metal rectangular expansion joints are often used on rectangular flues, and their shape is square and square, which is different from round tubes. Find out before you do it, otherwise the installation direction is reversed, and the pull rod will become a decoration. Do you believe it?
02 Do three things before dismantling: mark, take photos, and check the original condition
Remove it and throw it on the ground. When it is put back, I can't remember which side is facing upward and which grid the tie rod nut is screwed to. Dude, can't you just take two minutes to make a mark?
- Mark flange position:Use a marker to draw an arrow on the expansion joint flange and pipe flange, aligned symbols, such as "↑A" versus "↑A".
- Photo Archive:Take three shots sideways with your phone – front, side, tie rod nut details. Especially the length of the tie rod, it is best to measure the distance from the nut to the end of the screw rod in the original state with a ruler and write it down.
- Check the original state:See if the loose nut on the tie rod is loose? Some factories are pre-tensioned at the time of leaving the factory, while others are loose. This state determines whether you want to adjust it when you put it back.
If there is an arrow mark on the expansion joint, that arrow generally points to the flow direction of the medium. When taking photos, pay special attention to taking clear photos.
03 Formal installation: adjust pull rod, pair of arrows, leave pre-stretching amount
Okay, now you have the removed expansion joint in front of you, and the flange on the pipe is cleaned. How to install?
Step 1, adjust the tie rod nut. Note that the role of the tie rod is to restrict the axial displacement of the expansion joint under pressure, but also to allow it to expand and contract freely. So the tie rod can't be completely locked.How to adjust the tie rod nut of expansion joint？ The common practice is: first screw the nut to the root of the screw rod, and then retreat 1~2 turns, so that the tie rod has a gap of 0.5~2mm (depending on the size of the expansion joint). This gap is the "vitality", which ensures that the tie rod will not hold the bellows during thermal expansion and contraction.
Step 2, on the arrow.The direction of the arrow of the expansion joint refers toDirection of media flow. Don't install it backwards, otherwise the guide tube will hinder the flow of the medium and even cause howling. Take out the photos taken before and compare them. The arrow must be consistent with the flow direction of the pipe.
Step 3, leave the amount of pre-stretch. When installing metal expansion joints, if the pipe is cold, the amount of thermal expansion needs to be considered. Generally, manufacturers will mark "pre-stretching amount" in the product manual, such as forHigh temperature axial expansion joint, may require a pre-stretch of 20 mm. How to operate it? Mark the tie rod, then use a jack or special tool to pull the expansion joint to the specified length, and then lock the tie rod nut. Note:Correct installation method of expansion joint of large tie rodThere is a key-the tie rod must be symmetrically adjusted on both sides, and cannot be tightly loosened on one side, otherwise the expansion joint will be crooked.
04 Sealing and Fastening: The Difference Between Metal and Non-Metal You Have to Know
This step is the easiest to roll over. The sealing methods of metal expansion joints and non-metal expansion joints are completely different, so don't mix them.
Metals:Such asUniversal corrugated expansion joint、Direct buried (fully buried) type expansion jointThey are sealed by flanged gaskets. The material of the gasket should match the medium. Graphite gasket or metal-wound gasket is generally used for flue gas pipelines. When tightening the bolts, tighten them three times in diagonal order. The torque value can refer to the value given by the manufacturer. No data? Then use a standard wrench to screw it until you feel "eating hard" and then take half a turn. Don't screw it to death. The flange of the bellows is thin and easy to deform.
Non-metallic:LikeNon-metallic expansion joint (fabric fiber expansion joint)、rubber compensatorTheir own fabric or rubber layer is the seal, and the flange surface is usually pressed against the bead. When installing, pay attention to the bolts of the strip should not be pressed too tightly, otherwise the fabric will be crushed; It can't be too loose either, otherwise it will leak. My own experience is: first twist it with your fingers until it just touches, and then twist it half a turn to one turn with a wrench, so that the pressing strips compress the fabric evenly, but the fabric is not obviously deformed.
Rectangular non-metallic expansion jointIt is very common in the flue, and its four corners are easy to leak. When installing, it is necessary to specially check whether the pressure plate at the corner fits.
05 Don't go in a hurry after installation, do a simple displacement test
You think you're done by tightening the bolts after installing it? That's naive. We have to verify if the tie rod is really a decoration.
How to measure? Just do it manually:
- Push the expansion joint with your hand and feel if it can expand and contract freely. If it does not move at all, it means that the tie rod is locked. Loosen the tie rod nut quickly.
- If it is a non-metallic expansion joint, pinch the fabric layer with your hand to see if there is an abnormal bulge or dent.
- If possible, check with a gauge to see if the pre-stretch gap of the expansion joint is still there. For example, a gap of 2mm was left before, but now the gauge can be stuffed in, which means that the tie rod is not crushed.
If it is a double tie rod construction, such asCompound hinge transverse expansion jointIts tie rods appear in pairs, so it is necessary to ensure that the force on both sides of the tie rods is uniform. You can tap the lever lightly with a wrench to hear if the sound is consistent-crisp means free, dull means stuck.
Finally, turn on the fan or induced draft fan, run at a small flow for a while, keep people away, listen to whether there is any abnormal noise, and see if there is any air leakage at the flange. No problem, congratulations, the flue expansion joint restored and installed successfully!
Tsk, it seems to be quite a lot to write down, but if you really follow this process, you'll get it done in half an hour. The key is not to be lazy-mark, adjust the pull rod, leave the gap, measure the displacement, which step is saved, and there will be trouble behind. Do you think that's the truth?