Гидравлический пресс

Design And Analysis of Hydraulic Press Circuit

Design And Analysis of Hydraulic Press Circuit

Приблизительное время прочтения: 22 минут

Hydraulic Press Circuit

In modern machinery, the applied hydraulic transmission system is composed of some basic circuits. The so-called basic circuit is a typical oil circuit composed of related hydraulic components to complete specific functions. By mastering their working principles, composition, and characteristics, these circuits can be selected correctly and reasonably according to the machine’s working performance, requirements, and working conditions to form the complete hydraulic system required. Hydraulic Press Circuit

Конструкция контура регулирования давления

Контур управления давлением - это контур, в котором используется клапан управления давлением для управления всем или частичным давлением в системе. Контур давления, управляемый клапаном давления, может использоваться для управления стабилизацией напряжения, декомпрессии, наддува и многоступенчатого регулирования давления для удовлетворения требований приводов с точки зрения силы и крутящего момента. Клапаны давления стандартных компонентов включают в себя перепускные клапаны, редукционные клапаны, клапаны последовательности и односторонние редукционные клапаны, а также односторонние клапаны последовательности, которые объединены параллельно с односторонними клапанами.

A pressure regulating circuit is a system that controls operating pressure so that it does not exceed a certain – pre-tuned value, or so that the working mechanism has different pressures during the various stages of movement. Hydraulic Press Circuit

1. Выбор метода регулирования

  • Контур ограничения давления

A relief valve is best used to limit the maximum pressure in a hydraulic circuit. Figure 1 shows a common circuit for pressure processing machinery. The low-pressure relief valve1 is used to maintain the piston from falling by its self-weight when the piston of the cylinder rises (not working) to the end. This saves power consumption and avoids the heating of oil from the relief valve. Hydraulic Press Circuit

  • Pressure remote control circuit Hydraulic Press Circuit

As shown in Figure 2, when the solenoid three-way valve is demagnetized, the circuit pressure is set at 10MPa for the main relief valve; when the solenoid three-way valve is excited and the path between the main valve and the remote relief valve a or b is changed through the four-way solenoid valve, the pressure of the main circuit can be converted to 7MPa or 5MPa. The capacity of each valve, except for the main valve, all other small flow valves are used. Hydraulic Press Circuit

1. Pressure limiting circuit                                                              2. Pressure remote control circuit
1. Pressure limiting circuit    2. Pressure remote control circuit
  • Вторичный контур регулирования давления

In Figure 3, when the cylinder piston rises, falls and the piston remains in the highest position, the oil circuit pressure is p2=5MPa (the left high-pressure pump unloads). However, when the piston reaches the bottom, the load increases, and the pressure relay acts to manipulate the solenoid three-way valve so that p1=10MPa and high-pressure oil enter the circuit. Hydraulic Press Circuit

3. Secondary pressure regulating circuit   4. Pressure regulating circuit for compound pumps
3. Secondary pressure regulating circuit   4. Pressure regulating circuit for compound pumps
  • Контур регулирования давления для составных насосов

In the design, the capacity of the pump must be adapted to the requirements of work and reduce the generation of unwanted heat at low-speed drives. The Figure 4 circuit is electrically controlled and can operate at various flow rates and oil pressures as required to maintain maximum circuit efficiency, with the advantages offered by a pressure compensated variable pumps. The operating oil circuit of the electro-hydraulic reversing valve in the circuit is led from the remote port of the relief valve, preventing shocks caused by the switching of the main reversing valve. Hydraulic Press Circuit

2. Регулировка параметров давления.

  • Неправильная настройка давления предохранительного клапана

The set pressure of the relief valve is not appropriate, resulting in the hydraulic cylinder movement speed does not meet the requirements. Figure 5 circuit requires smooth movement when lifting, a large range of speed adjustment and the piston can stop at any position. But in operation, when adjusting the rising speed of the lift, the speed does not change in a wide range, only when the throttle valve opening is adjusted to a very small, the rising speed will change, not up to the proper performance requirements.

This is the reason why the pressure of the relief valve is adjusted high. The pressure of the relief valve should be set to the hydraulic pump working pressure is exactly equal to the hydraulic cylinder load pressure and pump all the flow through the throttle valve and the required pressure drop.

  • Improper pressure tuning parameters Hydraulic Press Circuit

Improper pressure setting parameters lead to high oil temperature in the constant pressure pump supply system. In the hydraulic circuit of the constant pressure pump shown in Figure 6, improper pressure setting parameters lead to high oil temperature during system operation. The reason for the above problem is due to the pressure valve 1 set system pressure Pr, lower than the valve 2 regulating spring set pressure Pt so that the constant pressure pump always work under the maximum displacement, excess flow to pressure Pr,

overflow back to the tank, and all transformed into heat so that the system temperature rises, so the valve 1 as a safety valve, the pressure is adjusted to the highest pressure than the system required 0.5 ~ 1MPa, the above problem can be solved. Hydraulic Press Circuit

5. Displacement lift hydraulic system         6. Constant pressure pump hydraulic circuit   1-            Pressure valve 2-Valve
5. Displacement lift hydraulic system         6. Constant pressure pump hydraulic circuit   1- Pressure valve 2-Valve
  • Пример отказа регулировки параметра давления

In the quantitative pump pressure control circuit shown in Figure 7, the hydraulic pump is quantitative, and the three-way four-way reversing valve neutral function is Y type. Therefore, when the hydraulic cylinder stops running, the system does not unload, hydraulic pump outputs pressure oil all the pressure oil output from the hydraulic pump is overflowed back to the tank by the relief valve. The relief valve in the system is YF type pilot-operated. The structure of the valve is a three-stage concentric type. Hydraulic Press Circuit

. Проблемы: When the reversing valve in the system is placed in the neutral position and pressure of the relief valve is adjusted, it is found that the relief valve works normally when pressure value is below 10MPa; when pressure is adjusted to any pressure value higher than 10MPa, the system emits a screeching sound like a blowing flute, at which time the pressure gage pointer can be seen to vibrate violently. After testing, the noise was found to have come from the relief valve. Hydraulic Press Circuit

. Анализ: In the three-stage coaxial high-pressure relief valve, the main spool has two sliding spools with the valve body and cover. If the co axiality of the bore after the assembly of the valve body and cover exceeds the design requirements, the main spool cannot move flexibly, but stick to one side of the bore to do the abnormal movement.

When pressure is adjusted to a certain value, it will inevitably provoke the main spool to vibrate. This vibration is not the regular vibration of the main spool in working movement, but the high-frequency vibration caused by the main spool stuck in a certain position (at this time because the main spool is also subjected to hydraulic clamping force). This high-frequency vibration will certainly cause strong vibration of the spring, especially the regulating spring, and noise resonance.

In addition, since the high-pressure oil does not overflow through the normal overflow port, but overflows back to the tank through the stuck overflow port and the internal drainage channel, this high-pressure oil flow will emit a high-frequency fluid noise. This vibration and noise are excited under the specific operating conditions of the system, which is the reason why it does not squeal at pressures below 10 MPa. Hydraulic Press Circuit

7. Цепь количественного контроля давления насоса.
7. Цепь количественного контроля давления насоса.

. Решения: The manufacturing accuracy of the YF type relief valve is relatively high. The coaxiality of the inner and outer circular surface of the connecting part of the valve cover and the valve body, and the coaxiality of the outer circular surface of the three shoulders of the main spool should be within the specified range.

In addition, the damping hole on the main spool has a damping effect when the main spool vibrates. When the working fluid viscosity is low or the temperature is too high, the damping effect will be reduced accordingly, therefore, the selection of the appropriate viscosity of the fluid and the control system temperature rise too high is also conducive to vibration and noise reduction. Hydraulic Press Circuit

  • Проблема с ошибкой регулировки параметров давления
  • The pressure can’t be adjusted up. The main reason is that the regulating spring of the relief valve is too soft, wrongly installed, or omitted; the main valve damping hole of the pilot-operated relief valve is blocked, the slide valve is under the action of oil pressure at the lower end to overcome the liquid pressure of the upper chamber and the spring force of the main valve, so that the main valve moves up, the regulating spring loses its controlling effect on the main valve, so the main valve opens the relief port overflow at a lower pressure; the spool and the valve seat are not closed tightly, and the leakage is serious; the spool is stuck in the open position by burrs or other dirt. Hydraulic Press Circuit
  • The pressure is too high to adjust down.The main reason is that the spool is stuck in the closed position by burrs or dirt, and the main valve cannot be open; when installed, the inlet and outlet of the valve are connected wrongly, and there is no pressure oil to push the spool to move, so the spool cannot be opened; the damping hole in front of the pilot valve is blocked, resulting in the main valve cannot be opened. Hydraulic Press Circuit
  • Large pressure oscillation. The main reasons are air mixed in the oil; poor contact between the spool and the valve seat; the diameter of the damping hole is too large and the damping effect is weak; resonance is generated; the spool moves inflexibly in the valve body. Hydraulic Press Circuit

For the above problems, the circuit design, component selection, component parameters, and system adjustment, piping installation, hydraulic oil use, etc. Can be targeted to improve the processing. Hydraulic Press Circuit

3. Проблемы во вторичном контуре регулирования.

  • Проблема скачка давления

In the secondary regulating circuit shown in Figure 8 (a), when 1DT is not energized, the system pressure is regulated by relief valve 2; when 1DT is energized, the system pressure is regulated by relief valve 3, the pressure switching of this circuit is realized by valve 4, when the pressure is switched from p1 to p2 (p1>p2) because there is no pressure in the oil circuit between valve 4 and valve 3 before switching, so when valve 4 is switched (1DT is energized), the instantaneous pressure at the remote port of relief valve 2 drops from p1 to almost zero and then rises to p2, the system naturally produces a large pressure shock. Hydraulic Press Circuit

8. Secondary regulator circuit (I)1. Hydraulic Pumps2,3-Relief valve4. Two-position two-way solenoid valve
8. Вторичный контур регулятора (I)
1. Гидравлические насосы
2,3-предохранительный клапан
4. Двухпозиционный двухходовой электромагнитный клапан.

Метод исключения: As shown in Figure 8 (b), valve 4 is connected to the outlet of valve 3, i.e., the position of valve 4 is interchanged with valve 3. Since the remote control port from valve 2 to valve 4 is often filled with pressure oil, the system pressure drops from p1 to p2 when valve 4 is switched, which will not produce excessive pressure shock. Hydraulic Press Circuit

  • The problem of long boost time when regulating pressure Hydraulic Press Circuit

Во вторичном регулирующем контуре, показанном на рисунке 9, когда трубопровод дистанционного управления длинный и система переходит из состояния разгрузки (клапан 3 находится в среднем положении) в состояние наддува (клапан 3 находится в левом или правом положении. ), время наддува велико, потому что труба дистанционного управления подключена к залежи нефти, и масло под давлением должно сначала заполнить трубопровод дистанционного управления перед наддувом.

9. Secondary pressure regulating circuit (II)1 - hydraulic pump; 2 - pilot-operated relief valve; 3 - reversing valve;4 - two-position two-way solenoid valve; 5 - check valve
9. Вторичный контур регулирования давления (II)
1 - гидронасос; 2 - пилотный предохранительный клапан; 3 - реверсивный клапан;
4 - двухпозиционный двухходовой электромагнитный клапан; 5 - обратный клапан

Обратите внимание на вопрос: Try to shorten the remote control pipeline, and add a back pressure valve (or check valve) at the remote control pipeline return 5, so that there is certain pressure so that boost time can be shortened. In the remote regulating circuit, the minimum regulating value of the relief valve is increased, and at the same time, the fault of hysteresis in action is generated.

The reason for this failure is that the piping between the main relief valve and the remote pilot relief valve is too long (for example, more than 10m) and the pressure loss in the remote control pipe is too large. Therefore, the remote control pipeline should not exceed 5m in general. Hydraulic Press Circuit

4. Помехи между клапанами давления.

  • Гидравлическая система с двойным насосом

In the hydraulic system shown in Figures 10, hydraulic pumps 1 and 2 supply pressure oil to hydraulic cylinders 7 and 8, respectively, and reversing valves 5 and 6 are three-way, four-way, Y-type solenoid-operated reversing valves. Hydraulic Press Circuit

10. Double pump hydraulic system1,2-Hydraulic Pumps; 3,4-Relief valve; 5,6-Directional valve; 7,8-Hydraulic cylinder
10. Гидравлическая система с двумя насосами.
1,2-Гидравлические насосы; 3,4-предохранительный клапан; 5,6-ходовой клапан; 7,8-гидроцилиндр

. Проблема: When the hydraulic pump is started and the system begins to run, the pressure of relief valves 3 and 4 is unstable, and vibration occurs and noise is emitted. Hydraulic Press Circuit

Испытание показывает, что когда работает только один предохранительный клапан, его регулирующее давление стабильно, а явная вибрация и шум отсутствуют. Когда два предохранительных клапана работают одновременно, возникает вышеупомянутая неисправность.

From the hydraulic system, it can be seen that the two relief valves are not connected other than a common return line. The fault is caused by this common return line. From the relief valve structure performance can be seen, the relief valve control oil channel for the internal drain. That is, the pressure oil before the relief valve into the valve, through the damping hole into the control volume cavity, when the pressure rises, the hydraulic pressure acting on the valve to overcome the regulating spring, open the cone valve port pressure reduction,

the oil flow through the valve body orifice into the relief valve return cavity, and the main valve port overflow oil confluence through the return line together back to the tank, so in the relief valve return, Therefore, in the oil return line of the relief valve, the flow state of the oil directly affects the adjustment pressure of the relief valve. Hydraulic Press Circuit

Pressure shock, back pressure, and other fluid fluctuations directly on the pilot valve cone valve, so the pressure in the control cavity also increased, and shock and fluctuations, resulting in unstable pressure adjustment relief valve, easy to provoke vibration and noise. Hydraulic Press Circuit

. Решение: The oil return lines of the two relief valves should be placed back to the tank separately to avoid mutual interference. If due to some factors, must be combined back to the tank, should be combined after the return pipe thicker, and the two relief valves are changed to external leakage type, that is, after the cone valve mouth of the oil and the main valve return cavity is separated, a separate connection back to the tank becomes external leakage type relief valve. Hydraulic Press Circuit

  • Гидравлическая система подъемного стола

As shown in Figure 11 circuit, each circuit acts separately, the two circuits correspond to the same specifications of hydraulic components and the same piping diameter. Hydraulic Press Circuit

11. lifting table hydraulic system1,2-hydraulic pump; 3,4-overflow valve
11. Гидравлическая система подъемного стола
1,2-гидронасос; 3,4-перепускной клапан

Проблемы: When two hydraulic pumps start working at the same time, the pressure adjusted by relief valves 3 and 4 fluctuates greatly, and vibration and noise occur. Hydraulic Press Circuit

The test shows that when a pump starts a single-cylinder operation, the relief valve adjusts pressure stable, with no obvious vibration and noise. while when two pumps start at the same time, that is, when the two relief valves work at the same time, the above-mentioned failure occurs. Hydraulic Press Circuit

You can see Figure 11, the two relief valves share a common return line and no other connections. The fault lies in this common pipe. If the total return pipe is still designed according to the diameter of the separate circuit, when the two pumps supply oil at the same time, it will certainly increase the backpressure of the return port of the relief valve. Hydraulic Press Circuit

It can be seen that when the two pumps work at the same time, the laminar flow state, the total return line along the resistance loss increased by 1 time. Turbulent flow state, increased by 3 times, that is, the relief valve return port back pressure increased by 1 or 3 times. Hydraulic Press Circuit

From the relief valve structure and working principle, they control the oil to enter the control volume cavity through the damping hole on the main spool. When the pressure rises to overcome the pressure regulating spring force of the pilot valve, the pressure oil opens the pilot valve port,

and the oil flows through the valve port to lower the pressure and then flows into the return cavity of the relief valve through the drainage channel in the valve body and the oil overflowing from the main valve port converges and flows back to the oil tank together through the return pipeline. Therefore, the flow state of the oil flow in the return line of the relief valve directly affects the adjustment pressure of the relief valve. Hydraulic Press Circuit

When the two pumps work at the same time, the two relief valves share the same return line, the interaction of the two streams of oil flow, it is easy to produce pressure fluctuations, while the relief valve returns port backpressure changes significantly, under the mutual interference of these two factors, the pressure of the oil in the control cavity of the relief valve also changes, which will inevitably lead to unstable pressure adjustment of the relief valve, and accompanied by vibration and noise. Hydraulic Press Circuit

To eliminate the above-mentioned problems, you can increase the diameter of the return pipe of the two relief valves, and replace the two relief valves with external leakage type, that is, the oil flowing through the pilot valve orifice will flow back to the tank separately from the other leakage pipe, or configure the two relief valves with their return pipes to avoid mutual interference. Hydraulic Press Circuit

  • Multiple relief valve resonance problems Hydraulic Press Circuit

На рисунке 12 (a) насос 1 и 2 представляют собой количественные насосы одной и той же спецификации, при подаче гидравлического масла в систему, трехходовой четырехходовой реверсивный клапан 7 с нейтральными функциями для типа Y, предохранительный клапан 3 и 4 имеют одинаковые характеристики, соответственно, установленные в выходном отверстии насоса 1 и насоса 2 масляного тракта, для фиксированного сброса давления с. Давление предохранительного клапана установлено на 14 МПа, при запуске системы издается свистящий звук, похожий на сиреневый.

After debugging found that the noise from the relief valve, and found that when only one side of the pump and relief valve work, the noise disappears, both sides of the pump work at the same time, a whistling sound. It can be seen that the reason for the noise is the resonance of the two relief valves under the action of the fluid. Hydraulic Press Circuit

According to the operating principle of the relief valve, the relief valve is working under the interaction of liquid pressure and spring force, so it is very easy to Stimulates vibration and makes noise. Once the pressure oil at the inlet and outlet of the relief valve and the control port fluctuates, that is, the hydraulic shock, the main spool,

cone valve and its interaction with the spring in the relief valve should vibrate, and the degree of vibration and its state changes with the fluid pressure shock and fluctuation conditions. Therefore, the more stable the oil flow associated with the relief valve, the more stable the relief valve can work, and vice versa, it cannot work stably. Hydraulic Press Circuit

12. system with resonance of relief valve1.2 constant pump; 3.4 - relief valve; 5,6,9,10 - check valve; 7 - three-way four-way reversing valve; 8 - hydraulic cylinder; 11 - remote regulator
(а) система предварительного улучшения (б) улучшенная система
12. Система с резонансным предохранительным клапаном
1,2 постоянный насос; 3.4 - предохранительный клапан; 5,6,9,10 - обратный клапан; 7 - трехходовой четырехходовой реверсивный клапан; 8 - гидроцилиндр; 11 - выносной регулятор

In the above system, the pressure oil output from the double pump merges after the check valve, fluid shock and fluctuations occur, causing the check valve to oscillate, which leads to unstable pressure oil at the outlet of the hydraulic pump. And because the pump output pressure oil is originally pulsating, so the pump output pressure oil will fluctuate strongly, and provoke the relief valve vibration. And because the inherent frequency of the two relief valves is the same, it causes the relief valve resonance and emits abnormal noise. Hydraulic Press Circuit

Метод исключения: The exclusion method will relieve valve 3 and 4 with a large capacity relief valve instead, placed in the double pump merge, so that although the relief valve will also vibrate, but not too strong because of the exclusion of the resonance conditions. Hydraulic Press Circuit

. Смещение установочного давления двух предохранительных клапанов примерно на 1 МПа также может избежать резонанса. В это время, если рабочее давление гидроцилиндра составляет от 13 МПа до 14 МПа, значение настройки предохранительного клапана соответственно увеличится, так что минимальное давление настройки соответствует рабочим требованиям гидроцилиндра, а значение перепада давления По-прежнему следует поддерживать 1 МПа.

. Change the above circuit to the form of Figure 12 (b), that is, the remote control ports of the two relief valves are connected to a remote regulator 11, the adjustment pressure of the system is determined by the regulator and has no direct relationship with the pilot valve of the relief valve, but to ensure that the set pressure value of the pilot valve regulator spring must be higher than the maximum adjustment pressure of the regulator. Hydraulic Press Circuit

Поскольку диапазон регулирования давления дистанционного регулятора должен быть ниже, чем давление регулирования управляющего клапана предохранительного клапана для эффективной работы, в противном случае дистанционный регулятор не будет работать.

5. Проблемы с утечкой в масляном контуре управления предохранительным клапаном

In the circuit shown in Figure 13(a), the system has two oil supply systems because the equipment requires continuous operation and does not allow downtime for repair. When one oil supply system fails, the other oil supply system can start immediately to make the equipment run normally and then repair the failed oil supply system. Hydraulic Press Circuit

The performance specifications of the components of the oil supply system to which pump 1 and pump 2 belong are identical. The primary pressure is regulated by relief valves 3 and 4, and the secondary pressure is regulated by remote regulator 9. Hydraulic Press Circuit

However, when the system belonging to pump 2 stops supplying oil and only pump 1 is running, the system pressure does not go up, even when the electro-hydraulic reversing valve is placed in the middle position, pump 1 output oil circuit still cannot rise to the required pressure value. Hydraulic Press Circuit

13. relief valve control oil circuit leakage illustration1.2 - hydraulic pump; 3.4 - relief valve; 5.6 - check valve; 7 - reversing valve; 8 - hydraulic cylinder; 9 - remote regulator10-solenoid valve; 11,12-check valve
13. Иллюстрация утечки в масляном контуре управления предохранительным клапаном.
1.2 - гидронасос; 3.4 - предохранительный клапан; 5.6 - обратный клапан; 7 - реверсивный клапан; 8 - гидроцилиндр; 9 - выносной регулятор
10-электромагнитный клапан; 11,12-обратный клапан

After debugging, it was found that the maximum pressure of pump 1 could only reach 12MPa when running, and the design requirement should reach 14MPa. when the pressure regulator knob of relief valve 3 and remote regulator 9 were tightened, the pressure still could not go up. When the oil temperature is 40℃, the pressure rises to 12MPa; when the oil temperature rises to 55℃, the pressure can only rise to 10MPa. separately tested the pump and other components, no quality problems were found. The indicators meet the performance requirements. Components no problem, combined into the system pressure does not go up, should analyze the system components combined with the mutual impact. Hydraulic Press Circuit

When pump 1 is working, pressure oil enters the lower end of the main spool from the inlet of relief valve 3. And flows into the spring chamber at the upper end of the main spool through the damping hole. Then enters the spring chamber at the upper end of the main spool of relief valve 4 through the remote control port of relief valve 3 and the external oil pipe, and flows downward through the lower chamber of the main spool through the damping hole, and flows backward from the inlet of relief valve 4 into the discharge pipe of pump 2, which is stopped.  Hydraulic Press Circuit

Это будут две ситуации: а. обратный клапан 6 не закрывается; б. насос 2 из трубы давления масла заставит насос 2 как гидравлический двигатель обратного микродвижения или через зазор насоса 2 течет в резервуар. Таким образом, через порт дистанционного управления предохранительного клапана 3 происходит утечка гидравлического масла в бак, и происходит вышеупомянутый сбой давления.

Поскольку на линии управляющего масла установлено дросселирующее устройство, масло по масляной линии дистанционного управления предохранительного клапана 3 течет обратно в резервуар при определенных условиях сопротивления дросселированию, поэтому давление не полностью отсутствует. По этой причине предохранительный клапан 3 затем переполняется при давлении ниже требуемого.

На рис. 13 (б) показана усовершенствованная схема с обратными клапанами 11 и 12, выпускной патрубок в насос 2 отрезан, что устраняет указанную выше неисправность.

6. Проблема с закрытием выпускного отверстия гидронасоса

Figure 14(a) shows a pressure regulating circuit, which can switch the system pressure between the two pressures regulated by relief valve 1 and relief valve 2. When reversing valve 3 is in the left position, the system pressure is regulated by relief valve 1, and in the right position by relief valve 2, the system unload in the middle position.

System use for some time after the hose burst accident. After analysis: The unreasonable design of the system cause the accident. Reversing valve 3 in the process of doing pressure switching must go through a short process of valve mouth completely closed, in this process, because the pump output oil has no way to go, so that the system pressure suddenly rises, repeated pressure shock to make the hydraulic hose fatigue burst.

14. hydraulic systems using hoses1.2 - relief valve; 3 - directional valve
(а) неправильно (б) правильно
14. Гидравлические системы с использованием шлангов.
1.2 - предохранительный клапан; 3 - ходовой клапан

Одно из решений показано на рисунке 14 (б). Этот пример иллюстрирует: даже очень короткое закрытие выхода может вызвать сильный скачок давления в гидравлической системе, а если в системе нет шланга, это со временем неизбежно приведет к повреждению гидравлического насоса.

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  1. Аватар Simon Simon:

    Хорошая бумага!
    Можете ли вы прислать мне каталог вашего оборудования?

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