How to eliminate the defects of pressure control of hydraulic equipment

Update:17 Nov 2021

1. Measures to eliminate hydraulic shock of unloading a […]

1. Measures to eliminate hydraulic shock of unloading and reversing

The high-pressure and large-flow hydraulic circuit will have pressure shocks during unloading or reversing, and cause severe vibration. The basic methods to eliminate such problems are as follows.

(1) Pre-release the pressure in the circuit. When people release the pressure energy enclosed in the hydraulic cylinder in a proper way, and then manipulate the main hydraulic system, the pressure shock can be eliminated.

There is a two-position two-way solenoid valve in the upper cavity oil circuit of the hydraulic cylinder for pressure relief. When the work is completed and before the main reversing valve changes direction, the pressure relief valve is energized and connected with the help of a time relay for about 3 to 5 seconds. When the loop pressure drops to 0 or close to 0, the main reversing valve is switched on again. There will be no pressure shock. Note that the piping of the pressure relief valve must be small enough (within 6mm diameter), otherwise a new pressure shock will occur. The pressure relief circuit composed of the reversing valve and the throttle valve, that is, when the electro-hydraulic reversing valve 1 returns to the neutral position, the pressure in the upper chamber of the cylinder 2 is slowly released through the throttle valve 3 and the one-way valve 4, so the hydraulic cylinder moves upward No special pressure relief is required.

(2) Extend the time of pressure relief. Hydraulic control check valves are generally used for pressure maintenance and relief of large presses. During the pressure holding process of the hydraulic system, the energy stored in the compression of the oil, the expansion of the pipeline and the elastic deformation of the machine will be released suddenly when the pressure is relieved; the pressure in the upper cavity may not be completely released when the hydraulic cylinder returns to the end of the pressure holding process The pressure in the cavity has increased, causing the unloading valve and the main valve core of the hydraulic control check valve to open at the same time, causing the upper cavity of the hydraulic cylinder to suddenly discharge oil; the combination of the two increases the shock vibration and noise of the hydraulic system.

A one-way throttle valve is installed on the hydraulic control oil circuit of the hydraulic control check valve to control the flow through the hydraulic control port, thereby reducing the movement speed of the control piston, extending the pressure relief time, and eliminating pressure shocks.

Circuit to prevent hydraulic shock when the pump is unloaded. The outlet of the overflow valve 1 is provided with an anti-shock valve 2 to prevent shock when unloading. The anti-shock valve 2 is composed of a pressure reducing valve a and a throttle valve b. When the outlet of the electromagnetic reversing valve 3 is connected to the oil tank, it controls the outlet to discharge a certain flow, so that the overflow valve is slowly opened to relieve the pressure, avoiding the sharp drop in pressure. The impact.

For the proportional relief valve, the pressure relief time can be changed by adjusting the corresponding potentiometer on the amplifier circuit board.

2. Measures to prevent abnormal high pressure

The hydraulic system will generate abnormally high pressure due to the start-stop hydraulic shock, external force or component failure. The basic measure to prevent abnormal high pressure is to set an overflow valve in the circuit and slow down the hydraulic shock.

(1) Install a relief valve in the hydraulic circuit to prevent abnormal external force and high pressure circuits. When the cylinder 1 is stopped, the pressure in the cylinder rises due to the effect of inertia, and an overflow valve is provided to prevent abnormal high pressure.

Prevent circuits that cause abnormal high voltage due to non-operation of components. When the cylinder 2 is lowered, if the balance valve 1 fails and does not operate, abnormal high pressure is generated on the piston rod side. The relief valve 3 can be set to prevent this.

Prevent abnormally high-pressure circuits when stopped. When the hydraulic motor 2 drives a large inertia load and the reversing valve 1 returns to the neutral position, a large hydraulic shock is generated. The brake valve 3 is set to drain the compressed high-pressure oil, and at the same time, it can be removed from the oil tank through the one-way valve Inhale oil to fill the vacuum in the other side of the oil pipe to prevent cavitation.

(2) Mitigating hydraulic shock A circuit that uses a flow valve to slow down hydraulic shock. When starting, the electro-hydraulic reversing valve 1 and the electromagnetic reversing valve 2 change directions at the same time, the opening of the flow valve 3 is slowly opened, and the motor 5 moves slowly. When stopping, the opening of the flow valve 3 controlled by the electromagnetic reversing valve 2 is slowly closed to slow down the motor speed. At this time, the electro-hydraulic reversing valve 1 is in the middle position and the motor is completely stopped. The acceleration and deceleration time are adjusted by the throttling device.

Mitigation of hydraulic shocks can also be achieved by setting buffer measures at the end of the hydraulic cylinder and stroke throttling control.

3. Measures to prevent pressure interference

The hydraulic system of modular machine tools and metallurgical machinery generally has multiple cylinders working at the same time. The load of each cylinder is different, and the required working pressure is also different. If the same oil source is used, it will inevitably cause mutual pressure interference. Bringing an oil source will make the hydraulic system too complicated. The basic idea to solve this kind of problem is to isolate hydraulic circuits with different working pressures in an appropriate way.

(1) The one-way valve is used to isolate the hydraulic circuit. The one-way valve can maintain a higher pressure in the hydraulic circuit without being interfered by other factors. The loop pressure is prone to instantaneous sliding failure, mainly because the inlet pressure of valve 1 is disturbed by system pressure fluctuations. Setting a one-way valve 1 at the outlet of valve 2 can eliminate the fault.

(2) Use one-way valve and accumulator to isolate hydraulic circuits. Some hydraulic circuits require stable pressure. Setting one-way valve and accumulator in the circuit can isolate the main oil circuit and compensate for the pressure drop caused by internal leakage. , So that the loop pressure is always stable.