DIY bellows repair

The bellows-thermocylinder unit is designed to shut off gas to the main burner when the boiler reaches the specified temperature. This device works purely mechanically. The main mechanical meaning of the bellows operation is precisely in stretching and compressing its “accordion” from the pressure inside the bellows that increases with increasing temperature. Read more about the bellows device and its work here. If it is not entirely clear what we are talking about here.

This is how the bellows-thermocylinder assembly for the AOGV Zhukovsky gas boiler looks like.

It is clear that there are only two options for the boiler operation: with defective bellows, or with a working bellows... This will make it easier to explain and understand the following.

How does a boiler with a working bellows work?

Boiler start-up. The boiler is cold. We close the valve (1) located on the pipeline to the main burner (if it is open). Only AOGV Zhukovsky boilers are equipped with such valves. This is done so that when the button (3) of the solenoid valve is pressed, the gas flows only to the igniter. Firstly, this is so that the igniter, so to speak, will surely ignite. Secondly, this is due to the possibly low gas pressure, which sometimes drops to 80-60 mbar in a fierce winter. And it would be nice to “put all the gas on the igniter”. Thirdly, at start-up, when the boiler is cold, the bellows “accordion” is compressed and the lower valve of the Economy automation unit is always open. Its spring squeezes out. Details of the device of the Economy block - here. Therefore, when the button (3) of the solenoid valve is pressed, the gas flows, in addition to the igniter, to the main burner. Why “divide” the incoming gas into two parts?

If there are difficulties in understanding what we are talking about now, read about the valve equipment.

So. Press the button of the solenoid valve (3). The gas went to the igniter. We lit the igniter, waited 30-45 seconds and released the solenoid valve button. The button must remain depressed. After that, we gradually open the valve (1) of the pipeline leading from the block to the burner. The main burner immediately ignites and the boiler starts to increase the temperature. Set the temperature control knob (2) of the bellows to the desired temperature, say + 60 + 70 C. When the boiler sets the set temperature, the mixture inside the bellows begins to expand, the bellows “accordion” expands, presses on the stem and closes the gas access to the main burner. When the boiler cools down, the "accordion" is compressed, the spring presses the lower valve of the block, thereby opening the access of gas to the main burner. The burner lights up from a burning igniter. And this process continues until, for example, it becomes warmer outside, and we do not want to change the temperature in the boiler to a lower one.

This is where the first malfunction awaits us. More precisely, not a malfunction, but how you can easily and permanently break a perfectly working bellows. When the boiler is hot and you want to turn down the temperature, DO NOT ROTATE THE TEMPERATURE REGULATOR KNOB (2) , – let the boiler cool down. Ideally, let the boiler cool down to just below the temperature you want to set. This is how it is done. We close the valve of the pipeline (1) through which the gas flows from the unit to the main burner. In this case, the igniter will remain on fire as it did, and the boiler will quietly cool down. After that, we wrap the thermostat knob (2) to the position we need. We open the tap (1). It's all. If you start to tighten the handle "hot", you crush the already weak "accordion". The boiler is hot, the accordion is spread out in both directions, there is pressure inside the bellows.And we begin to squeeze and press on the bellows even more. The first time you can even get lucky - the bellows will not burst. And if you do this several times in a row, the bellows fails. This remark applies to all bellows, without exception, both for Russian blocks and imported ones (for example Eurosit 630 or Honeywell).

Symptoms of malfunction # 1. When twisting the knob of the temperature regulator (2), something like kerosene suddenly smelled. Or something else. Cotton when tightening the bellows nut "hot". These are signs that the bellows has broken.

Well, OK. The bellows was broken. It happened. How does the boiler work?

How does a boiler work with a defective bellows?

Moving along the entire chain from starting the boiler “cold” to opening the pipeline valve (1), we will not notice anything special. The only moment. After starting the main burner, the boiler will never shut down again. After this phrase, I myself even felt sorry for the poor boiler. Y-yes. Which will never turn off. So how does it work?

Symptoms of malfunction # 2. The boiler works “directly”. That is, - the flame on the burner is controlled only by the gas valve (1): more or less. The hot boiler does not react to the twisting of the temperature regulator knob (2).

This is the case. People broke the bellows and saw perfectly well that the boiler bellows was faulty and decided not to change the thermal bellows for now. And so it was. They began to live on, but there was one big drawback. They succumbed to the persuasion of modern masters and cut the circulation pump into the heating, making the circulation in the system forced. Cut off the old open tank, put a modern closed red one.
And what a miracle! They were suddenly turned off the light. The pump, of course, stopped. No one is at home. He took the boiler and rustled up to + 95 + 100C. There was very little time left for the boiler to boil when someone came. He turned off the boiler. And that gurgles inside. Then it turned out that the light would now be turned off 2 times a week. And, bypassing all the shopping steps and cost options, he and his wife decided that it would be much cheaper to install a new bellows and save the boiler when the lights are turned off, buying solar panels, a household power plant, an unformer, an uninterruptible power supply, a wind turbine, etc.

Symptoms of malfunction No. 3. (while guess, – not tested by time). At the designated temperature of +60, the boiler heats up to + 70 and turns off. In principle, everything is fine. Only there is some delay. Which, by the way, can then increase up to + 90C, if you do not touch anything. Let the boiler cool down. You turn it on. And again, slowly, over time, the shutdown temperature begins to rise.

Here the answers are as follows. If this happens on AOGV-11.6 Economy boilers, then they have an adjusting screw on the thermostat nut (2) at the bottom. More details here. If this phenomenon is observed on boilers with a capacity of 17.4 and above, then it is possible (but not yet confirmed by mass cases) "Bites" the rocker arm of the lower valve or the pin (see complete bulkhead and the device of the Economy gas block). In any case, when heated, the bellows accordion “disperses” and raises the lever, closing the gas flow going to the burner. If the gas closes with a delay, there is a microcrack in the bellows. The pressure is not enough. But this is just a guess. This was also observed in the import blocks Honeywell and Eurosit 630.

Symptoms of malfunction number 4. Applies to those who have boilers in pairs. For example, in the off-season, one boiler always works, and the other rests. If the boilers are in series, then the bellows of the idle boiler must be opened with full ... The boiler may not work, but it is hot. The bellows is closed, it bursts from the inside, but it has nowhere to go, and it bursts. Therefore, you can keep a new boiler in reserve for a long time in the system, and after starting it, you can find out that the bellows is already covered.

As of today, 10/24/2014, this is so far all the cases known to us associated with a malfunction of the thermal bellows.

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Repair of the automatic system of the gas boiler AOGV-17.4-3

Gasification of Russian settlements has been going on at a rather intensive rate recently. The main element of the equipment that is installed in every rural house is a gas boiler. The author of this material shares his experience in repairing the automation of the popular in rural areas gas boiler AOGV - 17.4-3 produced by the Zhukovsky Mechanical Plant.

Purpose and description of the main units of AOGV - 17.3-3.

The appearance of the heating gas boiler AOGV - 17.3-3 is shown on rice. one , and its main parameters are given in the table.

Its main elements are shown in rice. 2 ... The numbers in the figure indicate: 1-type breaker; 2- thrust sensor; 3-wire of the traction sensor; 4-start button; 5-door; 6- gas solenoid valve; 7-adjusting nut; 8-tap; 9-storage tank; 10-burner; 11-thermocouple; 12- igniter; 13-thermorigulator; 14-base; 15- water supply pipe; 16-heat exchanger; 17-turbulator; 18- bellows assembly; 19-water drainage pipe; 20-door traction interrupter; 21-thermometer; 22-filter; 23-cap.

The boiler is made in the form of a cylindrical tank. On the front side there are controls, which are covered with a protective cover. Gas valve 6 (fig. 2) consists of an electromagnet and a valve. The valve is used to control the gas supply to the igniter and burner. In the event of an emergency, the valve automatically shuts off the gas. Traction breaker 1 serves to automatically maintain the vacuum value in the boiler furnace when measuring the draft in the chimney. For its normal operation, the door 20 should freely, without jamming, rotate on the axis. Thermostat 13 designed to maintain a constant water temperature in the tank.

The automation device is shown in rice. 3 ... Let us dwell in more detail on the meaning of its elements. Gas passing through a purification filter 2, 9 (fig. 3) enters the solenoid gas valve 1... To valve using union nuts 3, 5 traction temperature sensors are connected. The ignition is ignited when the start button is pressed 4... On the body of the thermostat 6 there is a setting scale 9... Its divisions are graduated in degrees Celsius.

The value of the desired water temperature in the boiler is set by the user using the adjusting nut 10... Rotation of the nut leads to linear movement of the bellows. 11 and stock 7... The thermostat consists of a bellows-thermoballoon assembly installed inside the tank, as well as a system of levers and a valve located in the thermostat housing. When the water heats up to the temperature indicated on the dial, the thermostat is triggered, and the gas supply to the burner stops, while the igniter continues to work. When the water in the boiler has cooled down for 10 . 15 degrees, gas supply will resume. The burner ignites from the pilot flame. During the operation of the boiler, it is strictly forbidden to adjust (reduce) the temperature with a nut. 10 - this could damage the bellows. It is possible to reduce the temperature at the dial only after the water in the tank has cooled down to 30 degrees. It is forbidden to set the temperature on the sensor above 90 degrees - this will trigger the automatic device and turn off the gas supply. The appearance of the thermostat is shown in (fig. 4) .

Actually, the procedure for turning on the device is quite simple, and besides, it is described in the operating instructions. And yet, consider a similar operation with a few comments:

- open the inlet gas supply valve (the valve handle should be directed along the pipe);

- press and hold the start button. At the bottom of the boiler, a hiss of escaping gas will be heard from the pilot nozzle. Then ignite the igniter and after 40. 60 and release the button. This time delay is necessary to warm up the thermocouple.If the boiler has not been in operation for a long time, the igniter should be ignited 20.30 s after pressing the start button. During this time, the igniter will be filled with gas, displacing the air.

After releasing the start button, the igniter goes out. A similar defect is associated with a malfunction of the boiler automation system. Note that it is strictly forbidden to operate the boiler with the automatics turned off (for example, if you forcibly jam the start button in the pressed state). This can lead to tragic consequences, since with a short-term interruption of the gas supply or when the flame is extinguished by a strong stream of air, gas will begin to flow into the room.

To understand the causes of such a defect, let's take a closer look at the operation of the automation system. In fig. 5 shows a simplified diagram of this system.

The circuit consists of an electromagnet, a valve, a draft sensor and a thermocouple. To turn on the igniter, press the start button. The stem connected to the button presses on the valve membrane, and the gas begins to flow to the igniter. After that, the igniter is ignited.

The pilot flame touches the temperature sensor housing (thermocouple). After some time (30.40 s), the thermocouple heats up and an EMF appears at its terminals, which is sufficient for the electromagnet to operate. The latter, in turn, fixes the stem in the lower (as in Fig. 5) position. The trigger can now be released.

The thrust sensor consists of a bimetallic plate and a contact (fig. 6). The sensor is located in the upper part of the boiler, near the flue gas outlet pipe to the atmosphere. In the event of a pipe blockage, its temperature rises sharply. The bimetallic plate heats up and breaks the voltage supply circuit to the electromagnet - the rod is no longer held by the electromagnet, the valve closes and the gas supply stops.

The arrangement of the elements of the automation device is shown in Fig. 7. It shows that the electromagnet is covered with a protective cap. The wires from the sensors are located inside the thin-walled tubes. The tubes are attached to the electromagnet using union nuts. The body terminals of the sensors are connected to the electromagnet through the body of the tubes themselves.

The check during the repair of a gas boiler begins with the "weakest link" of the automation device - the draft sensor. The sensor is not protected by a casing, therefore, after 6.12 months of operation, it becomes "overgrown" with a thick layer of dust. Bimetal plate (see fig. 6) quickly oxidizes, which leads to poor contact.

Remove the dust coat with a soft brush. Then the plate is pulled away from the contact and cleaned with fine emery paper. It should not be forgotten that the contact itself must be cleared. Good results are obtained by cleaning these elements with a special spray "Contact". It contains substances that actively destroy the oxide film. After cleaning, a thin layer of liquid lubricant is applied to the plate and contact.

The next step is to check the integrity of the thermocouple. It operates in a severe thermal mode, since it is constantly in the igniter flame, naturally, its service life is much less than the rest of the boiler elements.

The main defect of a thermocouple is burnout (destruction) of its body. In this case, the transient resistance at the place of welding (junction) sharply increases. As a result, the current in the Thermocouple - Electromagnet circuit.

The bimetallic plate will be below the nominal value, which leads to the fact that the electromagnet can no longer fix the rod (fig. 5) .

The low value of the thermo-EMF generated by the thermocouple can be caused by the following reasons:

- clogging of the ignition nozzle (as a result, the heating temperature of the thermocouple may be lower than the nominal). "Treat" a similar defect by cleaning the pilot hole with any soft wire of a suitable diameter;

- by shifting the position of the thermocouple (naturally, it may not heat up enough either).Eliminate the defect as follows - loosen the screw that secures the liner near the igniter and adjust the position of the thermocouple (Figure 10);

- low gas pressure at the boiler inlet.

If the EMF at the terminals of the thermocouple is normal (while maintaining the signs of malfunction indicated above), then the following elements are checked:

- the integrity of the contacts at the connection points of the thermocouple and the draft sensor.

Oxidized contacts must be cleaned. The union nuts are tightened, as they say, "by hand". In this case, it is undesirable to use a wrench, since you can easily break the wires suitable for the contacts;

- the integrity of the electromagnet winding and, if necessary, solder its conclusions.

The performance of the electromagnet can be checked as follows. Disconnect the thermocouple lead. Press and hold the start button, then ignite the igniter. From a separate source of constant voltage to the vacated contact of the electromagnet (from the thermocouple), a voltage of about 1 V is applied relative to the case (at a current of up to 2 A). To do this, you can also use a regular battery (1.5 V), the main thing is that it provides the required operating current. The button can now be released. If the igniter is not extinguished, the electromagnet and the thrust sensor are in good working order;

First, the force of pressing the contact to the bimetallic plate is checked (with the indicated signs of malfunction, it is often insufficient). To increase the clamping force, release the lock nut and move the contact closer to the plate, then tighten the nut. In this case, no additional adjustments are required - the pressure force does not affect the sensor response temperature. The sensor has a large margin for the angle of deflection of the plate, ensuring reliable breaking of the electrical circuit in the event of an accident.

It is not possible to ignite the igniter - the flame flares up and immediately goes out.

There may be the following possible reasons for such a defect:

- closed or faulty gas valve at the boiler inlet,
- the hole in the igniter nozzle is clogged, in this case it is enough to clean the nozzle hole with a soft wire;
- the pilot flame is blown out due to the strong air draft;
- low gas pressure at the boiler inlet.

The gas supply is cut off when the boiler is in operation:

- actuation of the draft sensor due to blockage of the chimney, in this case it is necessary to check and clean the chimney;
- the electromagnet is faulty, in this case the electromagnet is checked according to the above method;
- low gas pressure at the boiler inlet.

All good. It just so happens that the hydraulic compensator breaks down and starts knocking, ringing, etc. Often in such a situation, people simply change the hydraulic lifter. Of course, you can do this, but the cost of one hydraulic compensator, although not large, is still noticeable. And if there are several hydraulic lifters to replace? All 16? The price tag starts to bite openly.

In fact, there is nothing to break down in the hydraulic lifter during operation, all breakdowns are associated with clogging of oil channels with dirt, which simply need to be flushed.

First you need to understand how to distinguish a non-working compensator from a good one. The core of a good expansion joint should not be pressed with a finger. If it is pressed through and returns to its place by the spring, then air has appeared in it.

This can happen for 2 reasons:

1) The hydraulic lifter was stored incorrectly for a long time, and oil slowly leaked out of it (new hydraulic lifters are always empty)
2) The oil channels of the hydraulic compensator are clogged with dirt, where it is necessary the oil does not pass, where it is not necessary it passes, and so on.

In the first case, you can simply put them on the car, and in 10 minutes they will pump over and start working correctly. In the second case, we need to clean it.

First of all, you need to open it. As practice has shown, this is the most difficult part of the repair. For opening, the core is simply knocked out of the case by strong blows of the open part of the glass on a hard surface through the fabric.I wrapped the glass in 4 layers of fabric, tying the ends of the fabric from the back in a knot and holding it.

Do not knock on thin hard materials such as plywood, etc., they “absorb” the impulse too much, making the task much more difficult. Most likely you will beat off your hands and not get the desired result. I knocked it out on the concrete floor, through thin linoleum (+ 4 layers of fabric), some advise doing it on a piece of wood, but it should be quite massive.

As a result, we have to get a separate case, and a separate core:

Core and body.
The core consists of a cylinder, piston and spring. The piston itself can be easily removed from the cylinder by hand.
The piston has a hydraulic valve that should be cleaned first. To open it, carefully pick out the valve cover with a thin screwdriver:

It is important that under the cover there are 2 small parts, a valve ball and a small spring (it has no flying properties, but it can roll). Here is the actual result of disassembling the core:

All this must be carefully washed so that there are no traces of dirt. Particular attention should be paid to the valve hole:

and a small hole at the bottom of the case (cup), visible in the first photo. Then we collect the piston. On the piston body, carefully, put the ball and the spring:

then we cover it all with a lid and, using a thin screwdriver, push the lid into the mount and put the piston spring on top:
and also, neatly, cover with a cylinder:
then turn over and carefully fill the glass with oil:

Using a thin rod, we push the valve ball, pushing the piston into the glass:

this operation will have to be done several times, slowly adding oil, until air stops coming out from under the valve. Having tried to press on the cylinder with your finger, you must make sure that the piston does not push through. If it works, then put it aside for now and grab the glass (body of the wetsuit). pour a little oil into it, and carefully insert the previously assembled core into it.

He pushes in there with his hands, but with good effort. I also recommend covering the housing oil supply hole with a cloth, from there it will sprinkle with oil.

Once again we check that the core is not pressed through, wipe it with a cloth and put it aside (ready for installation)
PS: Store the hydraulic lifter only with the open part of the glass facing up, as in the last photo.

Author; Dmitry Grigoriev Saint Petersburg

The exhaust system of any car, like other components and mechanisms, is prone to wear and tear. The reason may be various external factors - this is the duration of operation, the manifestation of corrosion, etc. One of the important component parts is the corrugation of the car's exhaust system. Despite its durability and strength, it also wears out. Therefore, in order for a self-made replacement of a muffler corrugation to be effective, it is necessary to have practical experience in repair work of this type.

The corrugation (bellows) is an important nodal element of a modern car that connects the engine to the muffler. It prevents mechanical deformation of the engine, thereby increasing the performance of the exhaust system.

Today, manufacturers produce two main types of these devices:

• Bellows with outer and inner braids, which are used only on cars with a gasoline engine. The outer braid of the corrugation prevents from strong vibrations, and the inner braid protects against deformations, which may subsequently lead to its breakage;
• Bellows with three braids, suitable for both diesel and petrol engines. It includes an additional inner braid made of durable tubing.

The bellows (corrugation) is the most vulnerable part of the exhaust system. Basically, mechanical damage to the device occurs due to uneven road sections, contact with stones and other solid objects.Also, clogging of the catalyst, improper dismantling of the muffler, excessive stretching, etc., negatively affects its operation. The most frequently damaged corrugation bends where moisture settles, as well as connecting seams.

It is not difficult to replace this device with your own hands, despite the fact that it is thin and can tear. First, we need to carefully remove it.

Consider one of the correct options for removing the device with your own hands:

• First you need to unscrew the nuts from the manifold and the front pipe;
• After removing the intake pipe, we proceed to cutting the old corrugation using a grinder. In the case when the device is under the manifold, it should be cut off carefully so as not to damage the flange and the pipe itself. It is advisable to remove the remnants of the old welding with a chisel.

Do-it-yourself technology for installing a new corrugation:

• First, you need to change the muffler rubber bands, and only then just install the front pipe in its place. It is important that it is in free float, and not compressed or curved;
• Having secured both parts of the receiving pipe, we proceed to the installation of a new corrugation. To do this, we need a welding machine in order to first grab it in several places, and then scald it at the joints;
• At the final stage, we put the front pipe together with rings and gaskets in place and put on the bracket.

As you can see, the process of replacing a defective corrugation with your own hands is not difficult, the main thing is to follow a simple technology and the result will be obvious. Sometimes situations happen that replacing the muffler corrugation did not bring a positive result. Such cases are very often present in practice and are usually associated with malfunctioning of other mechanisms of the car - wear of the engine cushion, due to strong engine vibration, etc.

To do this, it is better to use the services of specialized auto repair shops with high-precision diagnostic equipment and qualified specialists. With the help of diagnostics, you can find hidden defects in all components and mechanisms of the car and make repairs quickly and with minimal budget expenditure.

1. Ignition systems.
2. Fuel supply mechanisms.
3. Exhaust gas cleaning unit.
4. Engine parameters control unit.

To all of the above, it is worth adding a few notes:

• the release of moisture from the exhaust pipe should not cause any concern - this is normal for modern cars that are equipped with a catalyst;
• the liquid manifests itself due to the formation of condensation, because the outer part of the system is cooled more intensively than the inner, this is especially true in winter.

Quite often, you can find a situation when moisture appears as a result of a poorly performed earlier replacement of the acoustic filter bellows or its rotten housing.

On all machines, even new Mercedes GLS 2016 years, a mixture of gases is supplied from the cylinders to the inlet of the exhaust manifold, which includes the following components:

• carbon dioxide;
• oxygen;
• water;
• nitrogen oxides;
• carbon monoxide;
• unburned hydrocarbons.

Most often, a similar picture can be observed during the warm-up of the internal combustion engine. The crux of the matter is that the electronics give the command to enrich the combustible mixture. This is done in order to increase the exhaust temperature to heat the same catalyst, because its optimal operation starts around 300 ° C.
As a result of combustion, the mixture, which is far from stoichiometric, contributes to an increase in the concentration of unburned and carbon monoxide gases. It is this fact that leads to the intense formation of moisture. In this regard, the following points should be considered:

• prolonged and active driving effectively removes water from the acoustic filter, which prevents the formation of corrosion on the internal components of the system;
• short trips without preheating, especially in winter, tend to accumulate a large amount of moisture in the noise reduction device, which, when interacting with combustion products, forms an acid harmful to the metal.

Some car enthusiasts, when water flows from a car muffler, recommend drilling in its front and rear through a hole with a diameter 3-4 mm... In winter, this method will prevent frost formation in the catalyst.

An elastic connection to compensate for mechanical vibrations and temperature stresses most often becomes unusable for the following reasons:

• wall damage;
• breaks in the event of an increase in the pressure of gases in the system due to a breakdown of the catalyst;
• destruction of the engine mountings and exhaust system fasteners, which lead to unwanted vibrations;
• external defects of the unit due to exposure to chemicals that are applied to the road in winter.

• Bulgarian;
• heat-resistant paint;
• semi-automatic welding unit and related components.

The technological process of replacing the coupling requires the following points:

• using a grinder, cut out the defective part in the places where the braid and the adapter ring are connected;
• cut off the rings that are welded with the outer ends;
• eliminate the remnants of the weld;
• install a new part in its original place and weld it;
• treat the welding points with heat-resistant paint.

After completing the replacement of the corrugation of a car muffler with your own hands, you need to check the tightness of the connections. Gas leakage is detected visually when the engine is running. Additional recommendations will help to perform the work qualitatively:

• To facilitate installation, before starting work, it is necessary to mark with a core the places of joints of the expansion joint with the pipes of the exhaust system.
• Before installing the corrugation, pre-weld the ends of the double exhaust pipes.
• If there is not enough space for high-quality welding work, then repairs must be carried out on the dismantled exhaust unit.

The reason for the appearance of moisture lies in condensation processes with temperature drops. This factor manifests itself most intensively when the engine warms up and disappears after a long drive. For most modern cars, the symptom indicates that the catalyst and engine are working properly.

If defects are found in the vibration-isolating coupling, it is necessary to determine the reasons that caused its damage. To carry out repairs, it is enough to have a welding semiautomatic device and a grinder. The technology of the process consists of cutting off the defective part and welding a new one, followed by processing the seams with heat-resistant paint.

The bellows is the most reliable sealing element of movable joints relative to the external environment (see Fig. 19), which provides almost complete tightness and eliminates stem leaks.

Bellows are made from thin-walled pipes by plastic deformation of the metal. Bellows made of corrosion-resistant steel 08X18H10T are used in the NPP fittings.

Single-layer steel bellows according to GOST 17210-71 are manufactured with a wall thickness of 0.08 to 0.25 mm and an outer diameter of 8.5 to 125 mm. Multilayer steel bellows in accordance with the industry standard OST 26-07-857-73 can be manufactured with a wall thickness of 0.16; 0.20; 0.25; 0.32 mm and with an outer diameter of 22 to 200 mm. The number of layers of multilayer bellows is from 2 to 10.

Single-layer steel bellows according to GOST 17210-71 are manufactured with a wall thickness of 0.08 to 0.25 mm and an outer diameter of 8.5 to 125 mm. Multilayer steel bellows in accordance with the industry standard OST 26-07-857-73 can be manufactured with a wall thickness of 0.16; 0.20; 0.25; 0.32 mm and with an outer diameter of 22 to 200 mm. The number of layers of multilayer bellows is from 2 to 10.

The bellows is usually one (upper) end hermetically connected to the cover or clamped between the body and the cover, and the other (lower) end is hermetically connected to the spindle. Thus, the movable cap-spindle interface is sealed, and the bellows operates under the influence of external pressure. In this case, the spindle should only make a translational movement, and therefore a keyway or flat is provided in the valve spindles, which prevents the spindle from turning around its axis. The most convenient way to connect the bellows is TIG or roller seam welding using a pulsed current. Often, welding is done "on the mustache" (Fig. 59), in this case, two thin annular protrusions are welded, thereby creating an airtight overlap, which is easier to cut and then weld when replacing the bellows.

If traces of erosive wear, dents, scoring, scratches and other defects up to 0.5 mm deep are found on the sealing surface of the seat, the surface should be rubbed in. With a greater depth of defects, it is necessary to restore the sealing surface by surfacing, followed by machining and lapping (Fig. 50, 51).

To ensure high quality of surfacing of sealing surfaces on the trays, it is recommended to use the following method: surfacing on the tray is performed through a frame (jig) made of copper (Fig. 52), which contributes to the formation of body-shaped surfacing with minimal machining allowances (up to 1 mm). After surfacing, the surface is ground and lapped.

Table 8.9 shows an example of a process flow chart for repairing a bellows valve body.

The most commonly used methods for making bellows. Only seamless or longitudinally welded pipes are allowed for these fabrication methods.

Elastomeric formation

The pipe is inserted into a core containing a rubber cylinder. An axial force on the core stretches the rubber cylinder, forming bulges in the tube. After that, the load is removed from the rubber cylinder, and the bulge is compressed in the axial direction by an external force, forming a corrugation. The corrugations are formed one at a time. The pipe is shortened as the corrugations are formed.

Expansion (Core stretching method)

Individual corrugations are formed in the pipe by stretching the inner core. The plane partially minimizes the expansion, the pipe should turn slightly. The process is repeated until the required corrugation height is reached. Each corrugation is later dimensioned by means of special inner and outer rollers.

Hydraulic forming

The pipe is located in a hydraulic press or bellows machine. The surrounding outer stationary rings are located outside the pipe in the longitudinal direction at intervals approximately equal to the length of the finished corrugation. The pipe is filled with a substance, such as water, and the pressure rises to the pour point. The forming operation continues with simultaneous peripheral fluidity and is controlled by longitudinal shortening of the pipe until the desired configuration is achieved. This method can be used to produce one or several corrugations at once. Depending on the configuration of the bellows, some intermediate steps may be required, such as heat treatment. Balanced bellows can be made using balancing rings as part of the fixed plates. At the end, when the stationary plates are removed, the rings become an integral part of the bellows.

Pneumatic forming

This method is identical to elastomeric shaping except for the formation of an initial bulge by squeezing the rubber of the "inner tube".

Folding the corrugated sheet

The flat sheet is mechanically corrugated either by pressing or by rollers to obtain straight sections.This pre-formed sheet is rolled into a tube. The bellows is obtained by longitudinal welding of the sheet edges to each other.

Forming by rollers

The pipe is located in a bellows machine and one or more corrugations are formed by means of pressure from a roller. Usually the rollers are located on both sides of the pipe, inside and outside. The pipe can rotate relative to the rollers, or it can be stationary, and the rollers form the bellows by their rotation. The figure shows the first option.

Rolled up ring

A separate corrugation is made from a flat sheet and then folded into a ring. The edges of the ring are welded across the corrugation. If a bellows with more than one corrugation is required, the required number of rings are made, which are welded together.

Forming by pressing

The flat sheet is corrugated using a stationary press. This method is used primarily for the production of rectangular bellows. Using this method, different corrugation profiles can be obtained. The most commonly used are U and V profiles. The material and method possibilities limit the length of the profile. Longer lengths can be obtained by welding several profiles together.

Combined method

Some of the methods described in the previous paragraphs can be combined. One procedure for forming a toroidal bellows combines two methods. For example, a corrugation is formed by stretching and a height greater than the design height. Then, the corrugation is positioned between the rings of the mold, as in hydraulic forming. The rings are compressed and hydraulically formed a toroid as shown in the figure.