How to choose the flue expansion joint of condensing furnace? Step-by-step teaching you to avoid these pits

First, understand what is "special" in the flue of the condensing furnace-choose the wrong expansion joint, and be careful to leak in half a year

Don't think that the condenser flue is like the ordinary boiler flue. Just buy a general-purpose corrugated expansion joint and you can use it. If you do that, you'll have to cry for a new one in half a year. The flue gas discharged from the condensing furnace has a low temperature (usually below 100℃), but the humidity is extremely high, and the flue gas is full of acidic condensed water. This brings two fatal problems: one is acid corrosion, which ordinary stainless steel bellows can't bear at all; The second is the discharge of accumulated water. If the structure of the expansion joint is wrong, the condensed water accumulates in the corrugated valley, and the corrugation can be corroded in a few months.

Therefore, the first principle of choosing the flue expansion joint of condensing furnace is: acid corrosion resistance and drainage must be considered. There are two main schemes on the market: one is to add internal lining (such as PTFE-lined hose), and polytetrafluoroethylene is used to separate the metal from acid gas; The other is to directly use non-metallic expansion joints (fabric fiber expansion joints). The fabric itself is acid-resistant, and there are no water-accumulating dead spots of metal corrugations. Which of these two is more suitable? Just look down.

Second, three steps of selection: material, structure and size, one cannot be missed

Step 1: How to choose the material?

If the flue temperature of your condensing furnace does not exceed 120℃, non-metallic expansion joints (fabric fiber expansion joints) are preferred. Why? Because it is not afraid of condensate corrosion, and it is lightweight and easy to install. If you have to go on metal, you must choose PTFE-lined (PTFE-lined metal hose), or at least use 316L stainless steel, but to be honest, 316L can't last for years under long-term acidic condensate immersion. My suggestion: Don't struggle, go directly to the non-metallic expansion joint, worry-free.

Step 2: How to pick the structure?

Universal corrugated expansion jointOrHigh temperature axial type expansion joint Attention! Although the name of high-temperature axial type is "high temperature", its structure is also suitable for low-temperature working conditions, and the key depends on the displacement compensation amount. Generally, the length of the smoke pipe of household condensing furnace does not exceed 5 meters, and the axial displacement is within 10mm. Just buy a universal corrugated expansion joint. But if you have a turn in your flue or need to absorb large lateral displacement, considerCompound hinge transverse type expansion joint orCurved tube pressure balance type expansion joint. Don't be afraid of complicated names, the merchant will help you calculate.

Step 3: How to Size?

Measure the outer diameter of the flue. The inner diameter of the expansion joint must be consistent with the pipe. Attention! The joint between the expansion joint and the pipe shall haveguide tube(Refer to the question and answer of this site), the guide tube can guide the airflow and prevent the condensed water from flowing back. In addition, the length of the expansion joint should leave an installation allowance of 10-20mm. Don't buy just the right one, otherwise it can't be screwed on during installation.

3. Preparation before installation-don't rush to get started, check these things first

After you get the expansion joint, don't unpack it. Confirm three things against the list:

• Check Model: Metallic or non-metallic? Is it the right size? The product catalog of this site hasUniversal corrugated expansion joint、Non-metallic expansion joint、PTFE-lined hoseWait, look at the label on the package, don't get it wrong.
• Inspect seals: Non-metallic expansion joints usually have flanges. Is there a gasket on the flange surface? If you don't bring it, you need to match an acid-resistant rubber gasket yourself (this site hasrubber compensatorAndRubber PTFE compensator, take rubber PTFE, good corrosion resistance).
• Check installation space: Leave at least 50mm space around the expansion joint after installation, which is convenient for future maintenance. Don't put it in the corner of the wall, otherwise it's too late to cry during overhaul.

4. Teach you step by step to install the flue expansion joint of the condensing furnace (with key reminders)

Okay, let's do it now. Suppose you buy a non-metallic expansion joint (fabric fiber expansion joint), the installation steps:

1. Turn off the boiler and cut off power and gas。 Hey, you know this step without saying it, but someone really forgets it and gets scalded.
2. Remove straight pipe section of original flue, retaining the flange or ready to weld. Be careful to leave enough allowance when cutting, don't cut short. If you are not sure, don't cut it yet. Put the expansion joint on it and make a gesture.
3. Install a gasket on the expansion joint flange。 The gasket must be centered and not deviated, otherwise it will leak.
4. Insert the expansion joint into the flue, connecting bolts. Well, here comes the key reminder:Don't screw the bolts at once！ First pre-tighten diagonally, then tighten one by one, and the torque is even. This siteHow to adjust the tie rod nut of expansion jointIt was said in the Q&A that the nut should not be tightened too tightly, otherwise the ripples will be crushed to death.
5. Adjust expansion joint tie rod(if any). The ordinary condensing furnace flue does not need a tie rod, but if you buy one with a tie rodStraight pipe pressure balanced expansion jointIt is necessary to loosen the tie rod nut to just eliminate the preloading force, so that the expansion energy saving can expand and contract freely.
6. Check for skew。 After installing, measure it with a level ruler. The expansion joint cannot be crooked, otherwise the force will be uneven and the life will be halved.

After installation, power on and run for 5 minutes, and feel the surface of the expansion joint with your hand to see if there is any obvious vibration. If the vibration is severe, it means that the pipe support is not fixed properly, add aFlue baffle door orCircular flapper doors (double seals) may help, but it's another story.

5. Don't let go after installation: daily maintenance and common troubleshooting

Isn't it just an expansion joint? Just put it on and you're done? Tsk, what the flue expansion joint of the condenser is most afraid ofCorrosion of stagnant water。 So routine maintenance is just two things:

• Regular drainage: Install a drain valve at the lowest point of the flue, and open it after each furnace shutdown to discharge the condensed water. If there is no drain valve, remove the expansion joint once a month to clean the water, which is troublesome but no way.
• Appearance inspection: Take a quarterly look at the fabric layer of the non-metallic expansion joint for bulging and cracking. Once you find it, replace it immediately and don't delay it. Metal expansion joints (e.g.External pressure single axial expansion joint) If green rust or pitting corrosion is found on the corrugated surface, it means that corrosion has begun, so quickly change the lining with PTFE.

What to do if the expansion joint leaks? 90% of the reasons are aging gaskets or loose bolts. Tighten the bolt first, and if it still leaks, replace the gasket of the rubber PTFE compensator. What if the expansion joint is deformed? That 80% is that the displacement amount was not calculated correctly during the selection. Remember to find the manufacturer to recalculate it next time.

6. Finally, say a few words: When should I find a manufacturer to customize?

In fact, the vast majority of condenser flues use standard specificationsNon-metallic expansion jointThat's enough. But if your flue is special-shaped, such as many turns, strange pipe diameter, or it needs to absorb axial and angular displacement at the same time, then don't think about it yourself, and go directly to the manufacturer to customize it. You can say to the manufacturer, "I need oneNon-metallic expansion joint (fabric fiber expansion joint), acid resistant, with guide tube, flanged connection, displacement amount XXmm. " Manufacturers understand it as soon as they hear it. Professional manufacturers like this site, andCorrugated expansion joint for power station industry,Metal corrugated expansion joint in cement industry, although different industries, but the process is common. When customizing, pay attention to providing accurate working condition parameters, such as temperature, pressure, and medium acidity.

Alright, I have said everything I need to say. If you follow these six steps, you will basically not step on a pitfall. If you are still unsure, just take a few live photos with your mobile phone and ask customer service, which is ten times better than buying it blindly yourself.