Specialized in manufacturing compensators, expansion joints, baffle doors

How to connect a metal expansion joint? Find out which model to use first

I received a phone call from a customer two days ago, saying that the steam pipe leaked only three months after installing the expansion joint. I asked him what model he used, and the answer was "just an ordinary metal expansion joint". Tsk, that's the problem —Method of joining metal expansion jointIt's not a matter of screwing a wrench. If you choose the wrong model, the rest will be for nothing.

The universal corrugated expansion joint is suitable for pipelines with axial displacement as the main; Large tie rod expansion saves energy and carries lateral displacement, but tie rod is the core; Pressure balance type (such as straight pipe pressure balance expansion joint and curved pipe pressure balance expansion joint) is specially designed to deal with high pressure and large diameter, so that the blind plate force does not spread outside. There are also high-temperature axial expansion joints, external pressure single axial expansion joints, double hinge transverse expansion joints... Each structure determines its joining method difference. If you use the high-temperature type as a general-purpose type, the bellows will burn through directly. This is not a joke, but a real thing.

Key checks before installation: Should tie rods and screws be removed or left?

Many masters get the expansion joint, and when they see the tie rod and adjusting screw, they mutter: Is this a transportation protection or a permanent part?

For universal corrugated expansion joints and high temperature axial expansion jointsThe limit tie rod and adjustment screw that came with the factory must be removed or loosened to the designed position before installation. Why? Because their role is to prevent the bellows from being overcompressed or stretched when transported and hoisted. After the pipeline docking is completed, if the tie rod is still screwed to death, the expansion joint will lose its compensation function, which is no different from a section of steel pipe. Two days ago, in a power plant project, the workers didn't dismantle the tie rod, and the bellows bulged directly during the pressure test-the pressure was carried by the tie rod, but the bellows was damaged.

The large tie rod expansion joint and the tie rod on the pressure balance expansion joint are structural parts and cannot be disassembled! Because the big tie rod has to bear the blind plate force generated by internal pressure, you remove the tie rod, and the bellows deforms instantly. Therefore, be sure to look at the nameplate and drawings before installation, and distinguish between "transportation limit" and "working tie rod".

Detailed explanation of installation steps: key points of centering, welding and fixing brackets

Step 1, Align. The pipe flange surfaces must be parallel, and the deviation must be controlled within 1-2mm. If you take the level to hit it, if the bellows is twisted, the life will be directly discounted by 50%. Step 2, welding. If it is a welded expansion joint, fix it by spot welding first, observe the deformation amount, and then weld it in layers, and the thickness of each layer does not exceed the diameter of the welding electrode. The welding current should not be too large to prevent the heat-affected zone from burning the thin wall of the bellows. It is recommended to wrap a damp cloth around the outer wall of the bellows for cooling. The third step is to fix the bracket. Remember one principle: the first bracket at both ends of the expansion joint must be a fixed bracket or a guide bracket to prevent the axial thrust of the pipe from pushing the expansion joint askew. EspeciallyDouble hinge expansion joint of air-cooled island vacuum pipeFor this large-size product, the spacing of brackets must be made according to the design drawing, and one less bracket may lead to hinge failure.

Many on-site diagrams save trouble, and the expansion joint is directly welded to the unfixed pipe. As a result, as soon as the temperature rises, the pipe drifts with the expansion joint, and the compensation amount is all wasted. And guess what? Finally reworked and removed, the bellows has been permanently deformed.

Differences in joining methods of different types of expansion joints

• Universal corrugated expansion joint: Axial displacement, remove the limit pull rod during installation to ensure the free expansion and contraction of the bellows. Pay attention to the direction of the deflector-the arrow must point to the direction of the media flow, otherwise the deflector will be washed off.
• Large tie rod expansion joint: For lateral displacements, such as L-pipe corners. The pull rod cannot be removed during installation, and the nut should be adjusted so that the pull rod is in the force balance position. The FAQ asks "How to adjust the expansion joint tie rod nut"? Generally, it is pre-tightened to 80% of the design length first, and then fine-tuned after the pipeline hydraulic pressure test.
• Straight pipe pressure balanced expansion joint: Working bellows and balancing bellows at both ends with tie rods in the middle. During installation, the three chambers must bear pressure at the same time, so the tie rod should never move. Moreover, this kind of expansion joint usually comes with its own fixed bracket, and only a guide bracket needs to be set on the spot.
• Curved tube pressure balance expansion joint: More complex construction for elbow sections that need to absorb combined axial and lateral displacements. Pay attention to the coaxiality of flanges at both ends when installing, deviation more than 2mm will cause bellows to twist.
• Compound hinge transverse expansion joint: Consists of two hinges and a set of bellows that absorb only the lateral displacement in the plane. The hinge pins must be lubricated during installation and are not allowed to withstand torsional torque.

And there's alsoExternal pressure single axial expansion jointIts bellows is on the outside, subjected to external pressure, and the installation direction has strict requirements. The exhaust hole on the housing must face upward, otherwise the condensate will not drain out-this is where many novices roll over.

Post-installation commissioning and acceptance: displacement inspection and leak test

Measure the length of the expansion joint in the cold state with a dial gauge or vernier caliper and record the initial value. Then introduce the medium (water or gas), slowly raise the temperature to the working temperature, and measure the length again to see if the actual displacement is within the design range. If the actual displacement is larger than the design value, it means that the pipe fixing bracket has failed or the spacing of the guide bracket is too large. If there is no change, congratulations, you may have forgotten to remove the limit rod.

Leak tests must also be done. For corrugated expansion joints used in power station industry or metal corrugated expansion joints in cement industry, it is usually required to hold pressure at 1.5 times the design pressure for 30 minutes without leakage. Small diameter can use compressed air with soapy water, large diameter can use ultrasonic leak detector. Pay special attention to weld seams and bellows crests-that is where cracking is most likely.

Method of joining metal expansion jointIt is not an isolated operation, it has to be matched with pipe design, support arrangement, and media characteristics. The stress analysis of the same model, used in steam pipes and used in flue gas pipes, is completely different. So, don't use "universal type" as a universal plaster. If you are not sure, flip through the product information on the station, or ask the manufacturer's technical engineer directly-it is much more troublesome than thinking about it yourself.

The customer asked "Does it count as equipment"? Find out what a non-metallic compensator is

Two days ago, a purchaser of desulfurization projects called and asked, "Does the non-metallic compensator count as equipment? Our boss asked me to go through the equipment procurement process, but the finance said that this thing is a pipe fitting, and I argued for a long time." This problem is actually quite typical. You say it is a pipe, it does fit on a pipe; But you say it's just a pipe fitting, and it comes with flanges, with deflectors, with insulation, and even with tie rods and limit devices. Tsk, everyone was confused.

Non-metallic compensator, also called non-metallic expansion joint, fabric fiber expansion joint, rubber compensator, rubber PTFE compensator, is essentially a flexible connection device. It is composed of skin (fluorine adhesive tape, silicone cloth, PTFE, etc.), insulation cotton, steel structure frame, beading and bolts. Unlike metal expansion joints, which absorb displacement by bellows, non-metals are deformed by fibrous materials and elastomers. It absorbs a large range of heat displacement, compensation directions, and can also be resistant to corrosion and high temperature. Its shadow is everywhere in the flue duct of power station, the flue gas at the tail of cement kiln, and the inlet and outlet of desulfurization tower. Does it count as a device or not? Let's look down.

Classification by Industry Standard: Does it fall under "Pipe Accessories" or "Equipment"?

Look at the national standard JB/T 12235-2015 "Non-metallic Expansion Joint". The standard name says "Expansion Joint", and the catalog is classified in the machinery industry standard, juxtaposed with pumps and valves. However, in GB/T 20801 "Pressure Pipe Code", non-metallic compensators are classified as "pipe components" (that is, pipe accessories). This brings up an interesting situation: from the perspective of pipeline system, it is just a flexible section of pipeline; However, from the manufacturing and design point of view, it has independent structural design, bearing pressure calculation and fatigue life evaluation.

Metaphorically, like a turbocharger on a car – it counts as an accessory on the engine, but when you buy it separately, it's a piece of equipment. The same goes for the non-metallic compensator: it is responsible for thermal compensation in the pipeline, but in fact its skin, insulation, frame and seal have to be designed individually according to the working conditions. Have you seen which tube sells for 1500 and still have to do finite element analysis? A non-metallic compensator will do. So from the perspective of engineering procurement, I prefer to treat it as equipment. Otherwise? You buy it as a pipe fitting, but it can't be installed on site. Who is responsible?

Compared with metal expansion joints, are the "equipment properties" of non-metals weak or strong?

Metal expansion joints (such as general-purpose corrugated expansion joints and high-temperature axial expansion joints) usually only use bellows and end pipes, and their structure is relatively simple. However, the structure of the non-metallic expansion joint is more complicated: the skin is covered with at least three layers (anti-corrosion layer, airtight layer and insulation layer), the inner lining has a guide tube, and the outside has a steel frame and compression bolts. If it is a rectangular non-metallic expansion joint, the frame is still a welded part, which involves blanking, assembling, welding and airtightness inspection. Can such a set of things be called pipe fittings?

Let's talk about shopping. You can select the metal expansion joint according to the nominal diameter, pressure and compensation amount, but for non-metal expansion joints, you have to provide the medium composition (acid fog? Wet smoke?), temperature range (what is the instantaneous high temperature?), three-dimensional displacement (axial, transverse and angular), and installation space size. Here, can you tell me which pipe fitting requires such complex technical parameters? Therefore, the "equipment attribute" of non-metallic compensator is not only weak, but stronger than that of metal expansion joint. It is essentially a customized flexible structural component.

From power stations, cement to desulfurization flue gas, how to identify and select the type on site?

Non-metallic compensators used in power station industry, such as corrugated expansion joints used in power station industry, sometimes choose non-metallic, but more of them are rectangular non-metallic expansion joints used in flue ducts. When selecting the model, focus on the temperature-the flue gas temperature at the boiler outlet can reach 450℃, and the skin must be made of fluorine tape plus multi-layer ceramic fiber. Both metal corrugated expansion joints and non-metals are commonly used in cement industry, but the dust at the outlet of the preheater is large and the temperature fluctuates drastically, so the fatigue resistance of non-metals is better. Desulfurization flue gas is more typical-flue gas has high moisture content and is corrosive, and it is often used with flue gas baffle door and desulfurization flue gas baffle door. When purchasing on-site, some units classify it as "valve accessories" and some as "boiler auxiliary machines". Very few are thrown directly to the hardware vault anyway.

I have seen a power plant buy the non-metallic compensator as an ordinary pipe fitting. As a result, after the arrival, the flange bolt holes didn't match, and the skin material was wrong. Finally, it returned it and redone it. It delayed the construction period for half a month. What are you saying this isn't a device? The equipment must have technical agreement, drawing confirmation and factory inspection report. The standard of non-metallic compensator clearly requires air tightness test and withstand pressure test, and each one should be done. How can pipe fittings get this treatment?

Conclusion: Non-metallic compensators are equipment-but don't buy them as regular pipe fittings

Do non-metallic compensators belong to equipment? The answer is: in terms of functionality and how it is used, it is the device. You can go through the equipment procurement process, file according to equipment management, write technical agreements, and accept the goods. But the key is not the status, but how to use it. If you regard it as equipment, you will naturally pay attention to the selection parameters, installation specifications and later maintenance; If you regard it as a pipe fitting, there is a high probability that you will ignore the details of the installation direction, the fixed bracket setting and the skin tightness control. And those details are precisely the key to whether it can be used for its full life.

Alas, at the end of the day, the name doesn't matter, it's important not to treat it like a pipe that can bend. Next time someone asks you, "Is the non-metallic compensator considered equipment?" Let him see the test clause of JB/T 12235-light air tightness pressure test, which is enough to draw a clear line between it and ordinary pipe fittings.

What the hell are fixed rods on non-metallic compensators for? Don't wait until the equipment breaks

Although it is called "non-metal", in fact, the skeleton and fixtures are still inseparable from metal. Many people thought that the bright fixed rod was used for lifting or convenient transportation-two days ago, a customer asked me if this thing could be removed, and I thought it was in the way. Disassembled? You try to disassemble it. As soon as the pipe heats up, the compensator will directly blow you into a balloon. The role of the fixed rod is far more important than you think.

The core task of the fixed rod is one word: limit

Limit excessive tension or compression of the non-metallic compensator in the axial direction (i.e. along the pipe direction). The non-metal loop strap itself is soft and elastic, but it can't stand hard tugging. When the pipe is displaced by thermal expansion and contraction, the compensator should absorb this displacement, but if the displacement exceeds the design value, the ring belt will be torn or folded. The retaining bar acts like a seat belt, telling you: At most you can run this far, and it will be dangerous further forward. In fact, both ends of the fixed rod are connected with connecting pipes or flanges, and a preset installation length is locked by a nut to ensure that the compensator works within a predetermined stroke range.

What's the difference between it and the tie rod on the expansion joint? That's a good question. Tie rods are usually used for metal corrugated expansion joints (such as the general corrugated expansion joints and compound hinge transverse expansion joints in our station). Its main function is to bear the blind plate force generated by internal pressure and prevent the bellows from being crushed to death by axial thrust. The fixed rod of the non-metal compensator is more to bear external loads and limit excessive displacement. In terms of material, the fixed rod of non-metallic compensator is generally made of carbon steel or stainless steel, and the surface is anti-corrosion treated. After all, the supporting flue gas and dust environment is often very harsh-such as the "flue gas baffle door" and "rectangular non-metallic expansion joint" in our product list, which are often used in desulfurization and dust removal pipelines. When corrosive gas rushes, if the pole rusts, the strength will drop, and something will happen.

How to judge if the fixed rod is adjusted properly?

Our product information mentioned the question and answer of "How to adjust the tie rod nut of the expansion joint". Although it is a tie rod, the adjustment logic of the fixed rod is similar. The core parameter is the mounting length-this length must correspond to the free length of the compensator in the cold state. For example, the working temperature of the pipeline is 300℃. When it is installed in a cold state, the fixed rod should be artificially compressed or stretched to a certain amount, leaving a margin for thermal displacement. You fit too tightly, there's no room to stretch when it's hot; Loaded too loosely, the loop straps sag when cold. Many on-site failures, nine times out of ten, are that the nut of this pole is not screwed correctly.

Another real case. A non-metallic compensator is connected in parallel next to our "metal corrugated expansion joint in cement industry" used in a cement factory to absorb the vertical displacement. On-site workers suspected that the fixed pole was in the way, so they dismantled it privately. Results After half a year of operation, the non-metallic ring belt was partially torn and the air leakage was serious. Change the ring belt and shut down for two days, resulting in hundreds of thousands of losses. Later, when the engineer checked, it was the lack of fixed rods that caused the deflection displacement to exceed the standard. Think about it, a pole costs hundreds of dollars, and a circle belt costs tens of thousands of dollars. This account is not unknown.

Finally, let's be honest

When selecting, don't just stare at the material and temperature resistance grade of the ring belt. The design and material of the fixed rod should also be checked. Especially for large-size rectangular non-metallic expansion joints, pole cross-section, thread specifications, and the strength of connecting ear plates at both ends have to be calculated. If you are not sure, read directly the article "National Standard for Non-metallic Expansion Joints JB/T 12235-2015" in our station, which clearly states the requirements for structural parts. With this pole, the compensator really locks the safety bottom line.

1. What material is the non-metallic compensator made of? Let's start with the conclusion: Not all non-metals are afraid of fire

When many people hear the word "non-metal", they automatically associate "plastic", "rubber" and "flammable" in their minds. This idea needs to be corrected quickly. Non-metallic compensator-to be precise, the one on our websiteNon-metallic expansion joint (fabric fiber expansion joint)— — The main material is a composite layer of high-strength glass fiber cloth, silicone rubber coated cloth and polytetrafluoroethylene film. Glass fiber itself is a Grade A non-combustible material with a melting point of more than 1000°C. What is really likely to burn is the rubber coating on the surface or the PTFE for sealing-but neither is at once. Silicone rubber is a flame-retardant material, which extinguishes itself from fire; Polytetrafluoroethylene (PTFE) is virtually nonflammable and only breaks down toxic gases in extreme heat. Therefore, the answer to the question "Can a non-metallic compensator catch fire?" depends on where it is used, at what temperature, and what medium it contacts. Think about it, if the material itself could be burned, then the thousands of degrees of smoke in the flue of the power plant would have set it on fire long ago, and it would have lasted for decades?

Second, under which working conditions the non-metallic compensator may indeed burn? Don't take any chances, these cases are worth watching

Seriously, the most common fire scenario for non-metallic compensators is the flue gas duct. For example, desulfurization system, cement kiln tail, power station flue and other places. The smoke often carries unburned sparks, oil mist or pulverized coal. Two days ago, a customer from a cement factory called and asked,Rectangular non-metallic expansion jointWill it burn through? I asked him if there were any sparks in the pipes and he said that the electrostatic precipitator occasionally ignites. This is dangerous. Once the surface coating of the fabric is continuously burned by high-temperature sparks, the silicone rubber will carbonize. Then, although the glass fiber cloth does not burn, it loses its sealing performance, the smoke leaks out, the temperature is higher, and finally the whole compensator will be scrapped. Another situation is that there is a leakage of flammable media in the pipeline. For example, the tail gas of chemical plants contains benzene steam, which may ignite when it touches high-temperature surfaces. Remember one sentence: the non-metallic compensator is not a source of fire itself, but it is a "carrier of combustion support"-if its surface is stained with oil and coal tar, it is equivalent to providing fuel for the fire. And guess what? At the end of many fire accidents, they were not burned by the compensator itself, but the ash and oil accumulated around them were ignited.

3. How do manufacturers prevent fires? Flame retardant coating, multi-layer structure, plus explosion-proof layer

Since there are risks, regular manufacturers must have countermeasures. When we make non-metallic expansion joints, we will select materials according to the medium temperature and composition provided by customers. For high-temperature flue gas pipelines (above 400℃), the structure of "ceramic fiber cloth + stainless steel wire mesh reinforced layer" is generally adopted. The refractory temperature of ceramic fiber can reach 1260℃, and it is okay to directly fight the flame. In the case of spark shock, the non-metallic compensator will be covered with a metal protective net or a metal skin-this is actually a bit like the one on our websiteHigh temperature axial expansion jointThe idea is that the high-temperature axial type is pure metal, and the non-metal type is only used as an inner liner. In addition, fluororubber or PTFE coating itself has good flame retardancy, which meets the fire protection requirements in JB/T 12235-2015 standard. Another point: when installing, it is necessary to ensure that no combustible materials, such as oil rags and cables, accumulate around the compensator. This is a problem of on-site management, but many accidents are precisely here. We often tell customers: You bought a fireproof compensator, and as a result, there is a pile of pulverized coal piled around, which is the same as not buying it.

Fourth, the easiest pit for users to step on: confusing rubber compensator and fabric compensator

We have a product list on our siterubber compensatorAndRubber PTFE compensator, there are alsoNon-metallic expansion joint (fabric fiber expansion joint)。 Although they are all classified as non-metals, the temperature resistance grade is much worse. The continuous working temperature of ordinary rubber compensators (such as nitrile rubber and neoprene rubber) generally does not exceed 120℃, and the instantaneous temperature resistance may reach 150℃. Beyond this temperature, the rubber will soften, decompose and even burn. However, the temperature resistance range of fabric fiber expansion joint (non-metallic expansion joint) is usually between 200℃ and 650℃, and it can be higher if the right model is selected. Therefore, if the user uses a fabric compensator in low-temperature pipelines (such as air-conditioning water systems), it is overqualified; But if a pure rubber compensator is used on a steam pipe at 300℃, it is a joke with your life. Before, a customer consulted, saying that the temperature of their flue gas pipe was only 180℃, and they used a rubber PTFE compensator. As a result, it burned through half a year later. Only after asking did I know that the actual temperature fluctuation peak of the pipeline reached 220℃, and the rubber layer had been carbonized. Therefore, when selecting the model, you can't only look at the average value, but also the peak temperature, duration and whether there are sparks in the medium. Is that the case?

5. Fire prevention starts from type selection: collect these three hard indicators

First, it is necessary to clarify the maximum operating temperature, instantaneous overtemperature temperature and frequency of the pipeline. If it is smoke with Mars, skip the rubber directly, choose a fabric fiber compensator and add a metal explosion-proof layer. Second, see if the compensator has flame retardant certification. The national standard JB/T 12235-2015 has clear requirements for the combustion performance of non-metallic expansion joints, such as oxygen index and horizontal combustion grade. On our stationRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)Proof of flame retardant rating can be provided on demand. Third, don't ignore the installation environment. If the compensator is installed outdoors or has corrosive gases, the surface coating will age and the flame retardancy will decrease, requiring regular inspection and replacement. To put it bluntly, the deciding factor in whether a non-metallic compensator can catch fire is not whether there is "non-metallic" in the name, but whether you have put the right product in the right place. Choose right, it can hold thousands of degrees of high temperature; If you choose the wrong one, tens of degrees of oil fume can light it.

Let's ask a question first: Why use non-metallic ones if the pipeline is equipped with metal compensators?

Friends who have been in contact with power plants and cement plants know that metal parts can't bear corrosion and dust accumulation in high-temperature flue gas pipelines and desulfurization systems. Although the metal bellows has high strength, it will rust out in a few months when it encounters acidic medium and wet smoke. Non-metallic compensators use fabric fibers, rubber, PTFE and other materials to deal with these "soft knives". This site'sNon-metallic expansion joint (fabric fiber expansion joint)Andrubber compensatorIt is to make up for the shortcomings of metal parts-to put it bluntly, it is to wear a layer of "body armor" on the pipeline.

The structure is actually not complicated

A flexible loop strap, plus flanges, frame and insulation. The band material may be silicone cloth, fluororubber,PTFE (rubber PTFE compensator)。 The key lies in design: how can it be resistant to both temperature and pressure? Generally, multi-layer composite, inner layer insulation, outer layer sealing. Two days ago, a customer asked: YouRectangular non-metallic expansion jointDifference from round? To put it bluntly, rectangles are mainly used in square pipes such as smoke ducts, which have large compensation and convenient installation-and the four corners of rectangular pipes are prone to stress concentration, which can be digested by the flexibility of non-metals.

Function Article 1: Absorb multidimensional displacement

During thermal expansion and contraction, the pipe will expand and contract axially, yaw laterally and even twist angularly. Because of its flexibility, the non-metallic compensator can absorb the displacement in these directions at the same time, and is not afraid of twisting like metal bellows. Like those used in the cement industryMetal Corrugated Expansion Joints in Cement IndustryAlthough it can also be compensated, when encountering large rectangular flues, non-metallic rectangular expansion joints are more cost-saving and easier to maintain. Think about it, when the temperature of a flue dozens of meters long changes, the displacement is often more than ten millimeters or even tens of millimeters, and the metal parts will get stuck directly if they are not properly designed. The non-metallic band is like a "soft joint", which is not afraid of twisting.

Function 2: Carry high temperature, carry corrosion, and reduce noise

The pipeline behind the desulfurization flue gas baffle door of the power plant is not high in temperature, but the acid corrosion is serious, and the metal parts will rust through in a few months. useNon-metallic expansion joints (fabric fiber expansion joints)With PTFE lining, the life can be extended by two or three years. In addition, it has a vibration damping effect-the vibration of the fan is transmitted to the pipeline, and the non-metallic band can eat some energy, and the noise is low. Some data show that under the same working conditions, the non-metallic compensator can reduce the noise of pipeline system by 8~12 dB. Tsk, this thing is easier than a silencer.

Compared with metal compensators, what are the advantages of non-metal?

Low pressure capacity, cannot be used in high pressure steam pipeline. Moreover, non-metallic materials will age, and their life span generally has to be replaced after 3-5 years. What about that? Calculate clearly when selecting: the medium temperature exceeds 600℃ or the pressure exceeds 0.1MPa, and honestly use metal parts orHigh temperature axial expansion joint； Low temperature and low pressure, large diameter, corrosive media, non-metal is the first choice. Is that the truth?

Finally, a reminder of the main points of purchasing

The national standard JB/T 12235-2015 stipulates the technical requirements of non-metallic expansion joints, mainly depending on the material of the ring belt, compensation amount and connection mode. Pay attention to the direction of the guide tube during installation-refer to the Q&AArrow direction of expansion jointThe tie rod nut should be adjusted according to the on-site displacement, and do not screw it (see for detailsHow to adjust the tie rod nut of expansion joint）。 If you are not sure, you can compare this siteUniversal corrugated expansion jointAndRectangular non-metallic expansion jointProduct parameters, or just ask the technology – they have more experience than me.

In summary, the role of a universal non-metallic compensator? It is to solve the "difficult and complicated diseases" that metal compensators can't handle: high-temperature corrosion, multi-dimensional displacement, large-diameter special-shaped pipes, vibration and noise reduction. If you choose the right one, the equipment is worry-free; Wrong choice, post-maintenance is enough for you to drink a pot.