Don't be in a hurry to select the model, find out the problem of "jumping up and down" on the pump pipeline
When the pump is running, vibration, thermal expansion and contraction, and misalignment of pipeline installation-any of these three problems can make the pump body suffer. And guess what? When many pumping stations are disassembled during maintenance, the expansion joint has long been pulled off, and the pump shaft is crooked. The metal tube expansion joint is used to "cover the bottom"-it is not a high-end black technology. To put it bluntly, it is a flexible joint, but without it, the pump seal, bearing and even motor may be scrapped in advance.
To put it bluntly, the function of the metal pipe expansion joint for the pump is to "take the blame" for the pipeline system. All the unreliability of the pipeline — vibration, displacement, misalignment — it has to carry it. Choose the right one, and the life of the pump can be doubled; If you choose the wrong one, you will have to dismantle it once every six months. So, think clearly before you start: What kind of displacements does it have to bear? How high is the vibration frequency? Is the medium corrosive?
The first function: vibration absorption and noise reduction, so that the pump no longer "shakes into a sieve"
The pulse flow and mechanical vibration of the pump will spread along the pipeline. Over time, it is common for the pipe joint to be loose and the valve to get stuck. The corrugated structure of metal pipe expansion joints (such as our general corrugated expansion joints and metal hoses) can eat this part of energy like springs. According to the measured data, with a suitable expansion joint, the amplitude of the pump outlet pipeline can be reduced by more than 60%. The effect is immediate, not blown.
Mind you, it's not just a bellows here. The pump is used with high pressure and large vibration, so the pressure resistance and fatigue life of the expansion joint are stricter. For example, if you take an ordinary rubber compensator to cover the vibration of the high-pressure pump, it will crack for you in less than a month. The wall thickness, the number of layers and the material of the bellows of the metal pipe expansion joint must be matched according to the working conditions of the pump. For example, to transport corrosive media, PTFE-lined metal hoses or stainless steel bellows are used; For high-temperature working conditions, you have to choose high-temperature axial expansion joints-we have all these products, but don't try to be cheap when selecting models.
The second function: withstand thermal expansion and contraction, and don't let the pipeline "hard top" the pump body
When the pump delivers high-temperature media (such as hot water and steam), the pipe will elongate; It shrinks again on cold start. If the connection is hard, the thrust of the pipe acts directly on the pump flange, which can lead to leakage of the seal or deformation of the pump housing in the worst. At this time, we have to rely on axial expansion joints (such as our high-temperature axial expansion joints and external pressure single axial expansion joints) to absorb the displacement of tens of millimeters.
However, note that the compensation amount must be calculated accurately when selecting the model. Don't try to make do with a general-purpose model cheaply, but the result is that the over-stroke is cracked-then the gain is really more than the loss. As an example, the steam pipe temperature rises from 20°C to 200°C, and the pipe elongates by approximately more than 20 millimeters per 10 meters. If you match an expansion joint with a compensation amount of only 10mm, isn't that waiting for something to happen? Also, don't forget the deflector-it allows the medium to flow smoothly through the bellows and avoids scour wear. Our question and answer specifically talked about the function of the guide tube, you can look through it.
The third function: correct the installation error and leave some room for "inaccuracy"
On-site pipeline construction, how can it be 100% aligned? It's normal to deviate by a few millimeters or even a dozen millimeters. Tightening the screw to forcibly connect the pipe and the pump is equivalent to applying additional stress to the pump body. Metal pipe expansion joints (such as double hinge transverse expansion joints and straight pipe pressure balance expansion joints) can absorb these lateral and angular deviations, so that the pump end flange is not stressed.
I met a customer two days ago, saying that the pump always leaked oil, and it was useless to change the seal three times. Later, it was found that the pipe was crooked, and the problem was solved immediately after installing the expansion joint. What a typical thing you say! One of the roles of metal tube expansion joints for pumps is to contain these "imperfections". However, it should be noted that different structures should cope with different displacement directions: the transverse type of compound hinge mainly absorbs transverse displacement, the sleeve-type pipe expansion joint is suitable for large axial displacement, and the rotary compensator is used to compensate multi-directional displacement. Don't get confused when choosing a model.
When choosing a model, you have to know: don't just look at "can you use it", but look at "how to use it"
The pump is used with high pressure and large vibration, so the pressure resistance and fatigue life of the expansion joint are stricter. In our product library, such as directly buried expansion joints and large-diameter thick-walled expansion joints are suitable for high pressure and large flow, while rotary compensators and sleeve-type pipe expansion joints are suitable for large displacement occasions. There is another detail: the adjustment direction of the tie rod nut (refer to what we talked about in our Q&A) directly affects the installation effect, so don't install it backwards. The function of the expansion joint tie rod is to limit the excessive deformation of the bellows, but it generally needs to be loosened or adjusted to the working position after being installed in place-if you screw the nut to death, the expansion joint will become a rigid connection, and how can you compensate for the displacement?
In addition, when the medium temperature exceeds 400℃, stress corrosion may occur in ordinary stainless steel bellows, so high-temperature resistant alloy or external pressure single axial expansion joint should be used; If it is a slurry containing particles, the material and thickness of the guide tube must also be thickened. Don't be too troublesome, these parameters are a little worse, and the lifespan is ten times worse.
After all, the metal pipe expansion joint for pumps is a "flexible buffer zone"-it has to carry all the unreliability of the pipeline. If you take it seriously, the pump can run safely for five or six years; You make do with it, then wait for the pump to be disassembled once every six months. Therefore, the next time you equip the pump with an expansion joint, you should not only look at the parameters, but also think about: What kind of displacements does it have to bear? How high is the vibration frequency? Is the medium corrosive?