Universal expansion joint and ordinary expansion joint, from the appearance of how to distinguish at a glance?
In the dry plumbing business, who hasn't seen a few expansion joints yet? But when they really arrived at the scene, the universal type and the ordinary type were mixed together. At first glance, it was really easy to be confused. Two days ago, a customer sent a photo and asked, "Don't these two have corrugated pipes? Why is the price difference double?" Well, today, I'll make this matter clear from the appearance. You don't care if you are new or veteran, you can judge it in seconds after reading it.
First, look at the bellows structure first-one section or two sections?
That's the most straightforward difference. Common expansion joints, such as our commonUniversal corrugated expansion jointOrAxial type expansion joint, bellows is a complete, from end to end. You look down the tube and there is only one set of ripples, without any disconnect in the middle.
What about universal expansion joints? It has two sections of bellows. There is a straight pipe sandwiched in the middle, which is called "intermediate pipe" or "intermediate connection section" in the industry. From the side, the bellows is divided into two sections, and the naked straight pipe in the middle is particularly eye-catching. Like ourCompound hinge transverse expansion jointAndCurved tube pressure balance expansion jointAll have this characteristic in structure. Universal type is essentially composed of two bellows + intermediate pipe + a set of universal mechanisms. Therefore, as long as you see the bellows being "cut off at the waist", there is a section of metal light pipe in the middle, which is likely to be universal.
Of course, there are exceptions —Straight pipe pressure balanced expansion jointFrom the appearance, there is also a section of bellows and a section of end pipe, but it relies on a pressure balanced bellows instead of a gimbal mechanism, so don't get confused. The criterion is: whether there is a tie rod and a universal ring in the middle.
2. Tie rod and ring plate-is there any "double insurance"?
Ordinary expansion joints mostly come with no tie rods or just a set of single tie rods. Such asExternal pressure single axial expansion jointIt absorbs displacement by its own bellows and does not need a tie rod to limit the direction at all. WhileUniversal corrugated expansion joints are sometimes equipped with a single tie rod to prevent the bellows from over-stretching, but it is only a straight rod with both ends screwed to death and fixed direction.
The gimbal type is different. It must have double tie rods or a gimbal ring. If you look carefully, the two tie rods are X-shaped or arranged in parallel, attached to the two ring plates. The ring plate is sleeved at both ends of the bellows, and the pull rod passes through the ear plate on the ring plate, and then locks it with a nut. More importantly-the hinge point of these two tie rods is a cross pin structure, which allows the expansion joint to rotate freely in both directions (horizontal + vertical) at the same time. So externally, if you see two sets of tie rods, or a ring-shaped, gimbal ring with a cross pin, it's definitely the gimbal type. Like ourDouble hinge expansion joint for air-cooled island vacuum pipeline, that double-hinged design is instantly recognizable.
Some common expansion joints will also be equipped with two sets of tie rods, but that is usually a "limit tie rod" and can't rotate universally. How to distinguish? Simple-gently push the flanges on both sides of the bellows with your hand. If you can swing up, down, left and right, it is universal type; It can only move in one direction, which is the normal type.
3. End connection form-can the flange "turn"?
Both ends of ordinary expansion joints are either fixed flanges (bolt holes are welded to death in alignment) or pipes (welded directly to the pipe). Such asHigh-temperature axial expansion joint, the flanges at both ends are welded, you can't twist them.
The universal expansion joint almost has flanges at both ends, and this flange can be rotated. Why? Because the universal type absorbs angular and lateral displacements, the intermediate tube cannot rotate freely if the flange is welded to death. You see that the mounting bolt holes on the back of the flange are evenly distributed around the circumference, and there are no welding marks between the pipe and the flange, that is, the rotatable flange. Coupled with double tie rods, the whole structure is like a "universal joint".
The flanges at both ends of the universal type expansion joints are usually thicker than the normal type because they are subject to greater bending moments. Touch the thickness of the flange edge with your hand. The ordinary type is generally 6~12mm, while the universal type is often more than 16mm, or even thicker.
4. Nameplate and model number-secrets are hidden in the text
Don't just look at the appearance and draw a conclusion. The nameplate is ironclad. In the standard naming rules, the models of universal expansion joints usually have the letter "W" or "universal". For example, if you see the beginning of "ZW" or "WX", it is the gimbal type. Like oursThe transverse type expansion joint of compound hinge has the transverse code in the model, while the code of the universal type is "W".
But on the other hand, the one without the "W" is not necessarily not universal. In order to save costs, some manufacturers have simplified the structure of the universal ring, and only the words "expansion joint" are written on the nameplate. Therefore, the nameplate can only be used as an auxiliary judgment, so don't be superstitious.
Some duplex expansion joints (such asThe appearance of double straight pipe bypass pressure balance expansion joint is also a two-section bellows, but it does not have a universal ring, which relies on the principle of pressure balance. At this time, you have to combine the tie rod and steering freedom mentioned earlier to judge.
5. Actual combat experience-three key points to be identified at a glance on the spot
Having said so much, I can sum it up into three formulas, which will be applied directly next time I go to the construction site:
- Look at the structure:Is the bellows "one-section" or "two-section"? Two-stage + intermediate straight pipe → universal type candidate.
- Look at the pull rod:Is there a double tie rod or gimbal ring? The one with cross hinge is the universal type, and the single tie rod or limit rod does not count.
- Looking at steering freedom:Push the flange by hand, which can deflect in any direction → universal type; It can only move up and down or left and right in one direction → normal type.
You see a power plantThe power station industry uses corrugated expansion joints, and a circle of tie rods hoops the corrugated pipe tightly, but the flanges at both ends can't rotate-that is, the ordinary axial type. The other one is installed on the intermediate pipeline, with a straight pipe in the middle of the two sections of bellows, an X-shaped tie rod and a movable flange-a proper universal expansion joint. Is that the truth?
Speaking of this, I have to mention that the consequences of wrong judgment are serious. The ordinary type is installed on the pipe section that needs universal compensation, and the tie rod is deformed in the slightest case and the bellows is burst in the worst case.