예상 읽기 시간: 22 분

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

압력 제어 루프 설계

압력 제어 회로는 압력 제어 밸브를 사용하여 시스템의 전체 또는 부분 압력을 제어하는 회로입니다. 압력 밸브에 의해 제어되는 압력 회로는 힘 및 토크 측면에서 액추에이터의 요구 사항을 충족시키기 위해 전압 안정화, 감압, 부스팅 및 다단계 압력 조절의 제어를 실현하는 데 사용할 수 있습니다. 표준 부품의 압력 밸브에는 오버플로 밸브, 감압 밸브, 시퀀스 밸브, 일방향 감압 밸브 및 일방향 밸브와 병렬로 결합된 일방향 시퀀스 밸브가 있습니다.

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. 규제 방법 선택

• 압력 제한 회로

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

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

• 2차 압력 조절 회로

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

• 복합 펌프용 압력 조절 회로

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. 압력 매개변수 조정

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

• 압력 매개변수 조정 실패의 예

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

. 문제: 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

. 분석: 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

. 솔루션: 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

• 압력 매개변수 조정 실패 문제
• 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. 2차 조정 회로의 문제

• 압력 충격 문제

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

제외 방법: 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

그림 9에 표시된 2차 조절 회로에서 원격 제어 파이프라인이 길고 시스템이 언로딩 상태(밸브 3이 중간 위치에 있음)에서 부스팅 상태(밸브 3이 왼쪽 또는 오른쪽 위치에 있음)로 변경될 때 ), 원격 제어 파이프가 오일 풀에 연결되어 있고 압력 오일이 원격 제어 파이프라인을 먼저 채워야 부스팅되기 때문에 부스팅 시간이 길다.

질문 참고: 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. 압력 밸브 간의 간섭

• 이중 펌프 유압 시스템

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

. 문제: 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

이 테스트는 릴리프 밸브가 하나만 작동할 때 조절 압력이 안정적이고 명백한 진동과 소음이 없음을 보여줍니다. 두 개의 릴리프 밸브가 동시에 작동하면 위에서 언급한 오류가 발생합니다.

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

. 해결책: 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

• 리프트 테이블 유압 시스템

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

문제: 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

그림 12(a)에서 펌프 1과 2는 동일한 사양의 정량 펌프이고 시스템에 작동유를 공급하는 동안 Y형의 3방향 4방향 역전 밸브 7 중립 기능, 릴리프 밸브 3 및 4는 동일한 사양이며, 고정 압력 릴리프를 위해 펌프 1 및 펌프 2 오일 로드의 출력 포트에 각각 설치됩니다. 릴리프 밸브 압력은 14MPa로 설정되어 작동 시작 시 시스템 사이렌과 같은 휘파람 소리가 납니다.

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

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

제외 방법: 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

. 두 릴리프 밸브의 설정 압력을 약 1MPa 정도 엇갈리게 하면 공진을 피할 수 있습니다. 이때 유압 실린더의 작동 압력이 13MPa와 14MPa 사이이면 릴리프 밸브의 설정 값이 각각 증가하여 최소 설정 압력이 유압 실린더의 작동 요구 사항을 충족하고 압력 차이 값이 여전히 1MPa를 유지해야 합니다.

. 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

원격 레귤레이터의 조정 압력 범위가 릴리프 밸브의 파일럿 밸브 조정 압력보다 낮아야 효과적으로 작동하기 때문에 원격 레귤레이터가 작동하지 않습니다.

5. 릴리프 밸브 제어 오일 회로의 누출 문제

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

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

이것은 두 가지 상황이 될 것입니다. 체크 밸브 6이 닫히지 않음; NS. 파이프 압력 오일에서 펌프 2는 유압 모터와 같은 펌프 2를 마이크로 모션으로 만들거나 펌프 2의 틈을 통해 탱크로 흐릅니다. 따라서 릴리프 밸브(3)의 원격 제어 포트에서 작동유가 탱크로 누출되어 위에서 언급한 압력 장애가 발생합니다.

제어 오일 라인에 스로틀 장치가 설정되어 있기 때문에 릴리프 밸브 3의 원격 제어 오일 라인에 있는 오일은 스로틀 저항의 특정 조건에서 탱크로 다시 흐르므로 압력이 완전히 없는 것은 아닙니다. 이러한 이유로 릴리프 밸브(3)는 필요한 압력보다 낮은 압력에서 오버플로합니다.

그림 13(b)는 체크 밸브 11 및 12가 있는 개선된 회로를 보여주고 있으며, 펌프 2로 가는 출구 파이프가 차단되어 위의 결함을 제거합니다.

6. 유압 펌프 출구 폐쇄 문제

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.

솔루션 중 하나가 그림 14(b)에 나와 있습니다. 이 예는 매우 짧은 출력 폐쇄라도 유압 시스템에 큰 압력 충격을 유발할 수 있으며 시스템에 호스가 없으면 시간이 지남에 따라 필연적으로 유압 펌프 손상을 초래할 수 있습니다.

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