1. Why do you have to install an expansion joint at the pump outlet? Can you not pretend?
Many people think that the pump outlet pipe is hard, so it is more troublesome to weld it directly. But think about it, as soon as the centrifugal pump is started, the pressure pulses like a heartbeat, coupled with the impact of the water hammer in the pipeline, and the thermal expansion and contraction caused by the temperature change-if these forces are hard on the pump body, the mechanical seal will leak at least, and the pump housing will directly crack at worst. Expansion joints do just that: absorb displacement, dampen vibration, protect pumps and pipes.
But don't be too happy. Install the wrong position and choose the wrong type, that is to dig a hole for yourself. I've personally seen people putUniversal corrugated expansion jointOn the high-pressure pipeline at the pump outlet, the corrugated pipe was washed to pieces and scrapped in two weeks. Expansion energy saving solves the problem, but the wrong choice is the source of new accidents. What about that? Look down.
2. The first level of selection: pressure, temperature, medium, one wrong is all in vain
Pump outlet pressure is usually not low, and it is common for multi-stage pumps to dry to several MPa or even higher. At this time, don't rush to look at the design pressure of the pipeline, but you have to include the peak value of water hammer-the instantaneous pressure of water hammer may be more than 30% higher than the normal value, and ordinary expansion joints can't bear it at all. Therefore, the nominal pressure level must leave sufficient margin.
What about the temperature? Under high temperature medium, the material creep velocity of ordinary corrugated expansion joint will accelerate. At this time, either chooseHigh temperature axial expansion jointEither a deflector is installed to insulate the heat. Not to mention the corrosiveness of the medium-acidic and alkaline fluids must bePTFE-lined hoseOrPTFE compensatorOtherwise, the bellows will be perforated in a few months. Two days ago, a customer usedrubber compensatorI went to pick up oily sewage, but the rubber swelled and deformed, and it was wasted in two months. When selecting the product information of this site, don't rely on your feeling, that is to pay tuition.
3. Installation position and fixed bracket: 90% of installation accidents occur here
The expansion joint cannot be directly attached to the pump flange. You must leave at least a straight pipe section with a diameter length to stabilize the fluid flow. More importantly, fixing brackets or limiting brackets must be set on both sides of the expansion joint, and the main fixing bracket must be able to withstand the blind plate force. Many people think that expansion energy saving absorbs displacement and install it casually. As a result, as soon as the pipeline runs, the expansion joint is stretched to the limit, and the bellows directly cracks.
If you are usingCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointThen special attention should be paid to the adjustment of the tie rod nut. When installing, the tie rod nut must be loosened to the position corresponding to the design compensation amount, and never screw it to death. How to tune it? Refer to the question and answer of "How to adjust the tie rod nut of the expansion joint" in the station, which is very detailed. Alas, I have seen a project in which the worker screwed the tie rod so hard that the expansion joint couldn't move at all, which meant that it was not installed. Finally, the pipe stress pulled the pump body askew.
4. Flow guide and flow direction marking: Don't ignore these two small details
The medium flow rate at the outlet of the pump is fast. If the expansion joint has no guide tube, the high-speed fluid directly washes the inner wall of the bellows, and it won't take long to wear out. Especially for particulate-containing media, a guide tube is almost necessary. What is the function of the guide tube? In addition to anti-scour, it can also reduce flow resistance and avoid swirls. There is a special article in the Q&A of this siteSpecific Function of Expansion Joint Guide TubeYou can take a look.
In addition, there are generally arrows on the expansion joints to mark the flow direction-this arrow must point to the direction of the medium flow, and when installed backwards, the bellows will become unstable. Don't laugh, there are cases of acting backwards on the spot every year. EspeciallyLarge diameter thick wall expansion jointOnce installed backwards, the labor cost of disassembling and assembling will cost tens of thousands. And guess what? Last time, a brother from a power plant told me that a technician in their factory turned the arrow backwards, and as a result, the bellows bulged half an hour after turning on. So don't be too long-winded, check the direction of the arrow again against the drawing before installing.
5. Post-operation inspection and maintenance: Don't wait until you leak before you regret it
Installing expansion joints is not once and for all. The vibration frequency of the pump outlet is high, and the bellows is prone to fatigue cracks. It is recommended to check every six months: use soapy water to detect leaks, see whether there are corrosion spots or scratches on the surface of the bellows, and whether the tie rod and nut are loose. Especially for use under high temperature operating conditionsExternal pressure single axial expansion jointThe insulation layer must be done well, but don't wrap the bellows dead-leave room for inspection.
If you find that the bellows is seriously deformed, or the compensation amount has been exhausted, don't hesitate to change it directly. The service life of expansion joints depends on the working conditions: some can last ten years, and some are wasted in three years. Don't take chances and wait until it leaks before replacing it, the pump may have been damaged. By the way, there is a question and answer on this site called "The Service Life of Expansion Joints", which has a detailed analysis. You can refer to it.
Install the expansion joint at the pump outlet, not just buy one and install it. From working condition confirmation, selection, installation to maintenance, every link must be solid. Avoid these 5 pits so your pumps and pipes can live long.