3 Best Questions About Decompression Hydraulic Circuit
Estimated reading time: 8 minutes
Hydraulic Circuit using a pressure-reducing valve Figure 15 allows a cylinder or stroke in the circuit to operate at a low relief valve set pressure. A pressure-reducing valve with a check valve is designed so that when the piston returns, the oil flow passes through the check valve without passing through the pressure-reducing element. Hydraulic Circuit
1. The design of pressure reducing circuit to pay attention to the problem
- Leakage problem of pilot operated pressure reducing Hydraulic Circuit
Be aware of the pilot-operated pressure reducing valve leakage than other control valves. The leakage of this valve can be as much as 1L / min or more. As long as the valve is in working condition, the leakage is always present. In the choice of hydraulic pump capacity, take this into full consideration. It should note that the minimum adjustment pressure of the pressure-reducing valve should ensure that the difference between the primary and the secondary is 0.31MPa. Hydraulic Circuit
- Secondary pressure instability problem
The damping hole of the main spool of the pressure reducing valve is blocked so that the oil exported from the pressure reducing valve cannot flow smoothly into the capacitive cavity between the main valve and the pilot valve. And the pilot valve also reduces the control role of the secondary pressure exported from the pressure reducing valve, resulting in unstable secondary pressure. Hydraulic Circuit
2. Decompression Hydraulic Circuit component setting problem
As shown in Figure 16, the pressure in the branch circuit cylinder 2 after the pressure-reducing valve 3 is lower than the fluid pressure in the master cylinder 1 branch circuit, which is called a pressure reducing circuit. The problems of this circuit are as follows. Hydraulic Circuit
- When cylinder 2 is stopped for a long time, the secondary pressure after pressure reducing valve 3 gradually increases. This is because when cylinder 2 is stopped for a long time, a small amount of oil is discharged through the pilot valve through the spool gap to keep the valve in working condition. Due to the leakage in the valve, the flow through the pilot valve increases, and the secondary pressure (outlet pressure) of the pressure-reducing valve increases. To prevent this failure, you can add the oil circuit shown in the dashed line in the pressure reducing circuit, and install a safety valve at b to ensure that the pressure reducing valve outlet pressure does not exceed its adjustment Hydraulic Circuit.
- The speed adjustment of the hydraulic cylinder in the pressure reducing circuit is not working or the speed is not stable. As shown in Figure 16, this problem occurs when the leakage of pressure-reducing valve 3 (the fluid flowing back to the tank from the pressure-reducing valve drain port) is large. The solution is to change the throttle valve from the position in the figure to connected in series at an after the pressure reducing valve, to avoid the effect of pressure reducing valve leakage on the speed of cylinder 2. Hydraulic Circuit
3. Unstable working pressure of pressure reducing circuit
In the system shown in Figure 17, the hydraulic pump is quantitative, and the hydraulic cylinders 7 and 8 in the main oil circuit are controlled by two-position four-way electro-hydraulic reversing valves 5 and 6 respectively to control the direction of motion, and the control fluid of the electro-hydraulic reversing valves comes from main oil Hydraulic Circuit.
The pressure reducing circuit is connected in parallel with the main oil circuit and is depressurized by pressure reducing valve 3. The two-position four-way solenoid valve controls the movement direction of the hydraulic cylinder 9.
The electro-hydraulic reversing valve controls the return line of the oil circuit and the external drain of the pressure reducing valve. The oil circuit merges and return to the tank, and the operating pressure of the system is regulated by the relief valve2. Hydraulic Circuit
The main oil circuit in the system works normally, but in the pressure reducing circuit, the pressure downstream of the pressure reducing valve fluctuates greatly, so that the working pressure of hydraulic cylinder 9 cannot be stabilized at the regulated pressure value of 1MPa. Hydraulic Circuit
1 fixed pump; 2 – relief valve; 3 – pressure reducing valve; 4 a two-position four-way solenoid-operated reversing valve; 5,6 – two-position four-way electro-hydraulic reversing valve;
7 to 9 – hydraulic cylinder; 10 – pressure gauge
In the pressure reducing circuit, the downstream pressure of the pressure reducing valve, the working pressure of the pressure reducing circuit, occurs in large fluctuations is a frequent failure phenomenon, the main reasons for which are the following. Hydraulic Circuit
- The prerequisite for a pressure reducing valve to be able to stabilise the pressure downstream of the valve at the regulated value is that the upstream pressure of the pressure reducing valve should be higher than the downstream pressure, otherwise the pressure downstream of the pressure reducing valve cannot be stabilised. Main hydraulic circuit working pressure change significantly. Hydraulic Circuit
It will have a larger impact if the minimum pressure value changes lower than the downstream pressure of the pressure-reducing valve, this is because when the upstream pressure of the pressure reducing valve is increase, the downstream pressure may have to be increase instantaneously, but through the regulating action of the pressure reducing valve it will quickly return to the regulating valve. Conversely, when the upstream pressure of the pressure-reducing valve reduces, the downstream pressure of the pressure-reducing valve should reduce instantaneously, and the pressure-reducing valve will quickly adjust so that the downstream pressure rises to the regulated value. Hydraulic Circuit
If the upstream pressure fluctuates and its minimum pressure is lower than the fixed value of the downstream pressure, the downstream pressure has to be reduced accordingly and cannot stabilize at the regulated pressure value.
Therefore, in the main oil circuit actuator load changes in the operating conditions, when the minimum working pressure is lower than the pressure downstream, the design of the circuit should take the necessary measures, such as add a check valve, add an accumulator between the check valve and pressure reducing valve, etc., in order to prevent the pressure upstream changes below the pressure downstream.
- The load on the actuator is unstable. In the pressure reducing circuit, the downstream pressure is only stable due to the regulating effect of the pressure reducing valve. With the actuator has sufficient load, the downstream pressure still has to follow the objective law, that is pressure should be determined by the load. No pressure can form without load, and the pressure is lower with a low load. If the pressure reducing circuit, the pressure after the pressure reducing valve is set under the load condition at a certain moment, but in the working process of the pressure reducing circuit, when the load is reduced, the downstream pressure of the pressure reducing valve should reduce until zero. When the load increases again, the downstream pressure of the pressure-reducing valve increases, and when the pressure increases with the load to the regulating pressure of the pressure-reducing valve, the pressure does not increase with the load but remains at the regulating pressure value of the pressure reducing valve.
Therefore, under variable load conditions, the downstream pressure value of the pressure reducing valve varies, and this variation can only be lower than the regulating value of the pressure reducing valve, but not higher than the regulating value.
- There is back pressure in the external drain line. The control line of the pressure-reducing valve is an external drain line. the control fluid pushes the cone valve open and then returns to the tank separately. If external drain line has back pressure is changing, it directly affects the pressure of the pressure oil pushing the cone valve, causing a change in pressure and thus a change in the downstream operating pressure of the pressure reducing valve.
The fault phenomenon in the system shown in Figure 17 is analyzed by inspection and is caused by a change in back pressure in the pressure reducing valve external drainage oil circuit.
It is easy to see that the electro-hydraulic reversing valves 5 and 6 in the system is changing in the process of reversing the flow and pressure of the return oil in the control oil circuit. The oil in the external drainage circuit of the pressure-reducing valve is also fluctuating, and the two streams of oil merge to produce unstable backpressure.
After debugging, when the electro-hydraulic reversing valves 5 and 6 act at the same time, the pressure gauge 10 reads 1.5 MPa. This is because the electro-hydraulic reversing valve is under the action of a high-pressure control fluid, the instantaneous flow is larger, and in the case of a longer drain pipe, higher backpressure is generated, the backpressure increases. So that the main valve opening of the pressure reducing valve increases, and the local pressure at the valve opening decreases, so the working pressure of the pressure reducing valve increases.
To eliminate this fault, the pressure reducing valve’s drain line and the electro-hydraulic reversing valve 5 and 6 should be connected back to the oil tank separately, so that the pressure reducing valve’s drain line can flow back to the oil tank steadily without interference and fluctuation, and the downstream pressure will be stable at the regulated pressure value.
This above analysis shows that during the design and installation of the system, while understanding the working performance of the components, we should consideration carefully whether the components will interfere with each other.
Hi, do you have a single hydraulic press,thanks?