News
Test Method for Leakage of Hydraulic Valves
With the improvement of industrialization and automation level, hydraulic technology has developed into a complete automation technology including transmission, control, and detection. Although China's hydraulic industry started relatively late, driven by rapid economic growth and the demand for equipment manufacturing industry transformation and upgrading, the research and production of hydraulic components in China has also achieved rapid development.
1、 The drawbacks of current hydraulic valve testing
In order to save energy more, designers consider selecting low or no leakage hydraulic control valves when designing hydraulic systems, which puts higher requirements on the performance of hydraulic valves. Especially under the working conditions of maintaining load and pressure, the requirements for valve leakage will be higher, usually requiring a leakage rate of no more than 3 drops/minute. When such a requirement exists, design engineers usually choose lift type hydraulic valves, such as cone valve relief valves, cone valve solenoid valves, and so on.
The method for detecting leakage is currently not uniform for many factories, as shown in Figure 1. Although it is recommended in the GB/T 8105-87 Pressure Control Valve Test Methods and JB/T 10374-2013 Hydraulic Relief Valve standards to measure leakage by using a measuring cup or a small flow meter, the measuring cup needs to wait for one minute for the residual oil in the pipeline to be drained before measuring within one minute, Relatively low efficiency; When measuring with a small range flowmeter, on the one hand, the price of a small range high-precision cylindrical gear flowmeter is very high. Due to the fact that most flowmeters are volumetric, there is a certain volumetric efficiency, with a general accuracy of ± 0.5% F.S. For flowmeters with a range of 0-5L, the error is around 0.05 mL, so the accuracy is not even as intuitive and accurate as visually observed; On the other hand, due to the need to detect the characteristics at rated flow rate when testing the valve, and the limited range of the flow meter, it is necessary to switch between high and low flow rates, requiring a more complex control system.
2、 Research on Testing Methods for Leakage of Hydraulic Valves
（1） Electromagnetic valve testing
Similarly, electromagnetic valve products also need to test the pressure loss and leakage of the valve. The pressure loss needs to be tested at the rated flow rate, while the leakage amount needs to be tested at a particularly low flow rate. This also requires such devices, such as using a large flow meter for pressure loss detection, and using the following devices to detect leakage. This device is the same as before, but with two additional stop valves added. The main reason is that during the detection of the solenoid valve, the electromagnet needs to be powered on and off. When powered on or off, the valve will act. When operated at a certain speed, there will be a significant pressure impact. At this time, the impact will cause the one-way valve to discharge a portion of the oil to the tank, and there will be a certain amount of air in the pipeline between the tested valve and the one-way valve. At this time, it takes a long time to see the leakage amount, because the leakage must drain all the air and fill the pipe before it can drip from the burette.
（2） Improve the sealing effect of components
To improve the sealing effect of components, the first step is to ensure that the purchased sealing components themselves meet the requirements in terms of sealing quality, to avoid sealing damage during the assembly process of components. Before entering the site for installation of components, staff need to strictly follow the quality inspection regulations to conduct spot checks on the sealing performance of each component, ensuring that each assembled component meets the sealing requirements of the environment. Finally, during the assembly process of components, it is necessary to strictly follow the assembly regulations and follow the corresponding procedures, and conduct a trial run before operation to ensure that the hydraulic system components of the rolling equipment do not experience sealing failure during use.
（3） Diagnosis and detection of external leakage
As an important liquid used in hydraulic systems, the proportion of water in the emulsion reaches 95%, which makes the viscosity coefficient of the emulsion itself relatively small. At the same time, due to the large internal and external pressure differences in the hydraulic system, it can trigger fluid movement in the jet state. For the jet, the liquid pressure in the leakage direction is significantly higher than the atmospheric pressure in the nearby area. The expanding jet itself is not complete, and the surrounding gas will undergo periodic expansion and compression.
Under the above conditions, spherical structures extending to the vicinity at equal intervals on the jet boundary layer will appear. Such evenly spaced noise sources can stack radiation nearby, while the noise source is within the supersonic range of the jet. In view of this, it is clear that high-pressure liquid passing through the leakage location can emit ultrasonic waves. Therefore, based on the detection of ultrasonic sensors, the location of hydraulic support leakage can be explored.
When testing for leakage, the pressure valve needs to be in a fully closed state, that is, the system pressure of the test bench is gradually decreasing. After the valve is closed, the pressure continues to decrease by about 10%, and the leakage amount is observed. As the system pressure gradually decreases, the flow rate through the tested valve also gradually decreases. When the pressure valve is fully closed, the back pressure valve will seal the liquid in the pipeline. At this time, the volume of liquid dripping from the drip nozzle will be completely equal to the leakage volume of the liquid in the closed state of the valve. Generally, record the number of drops within 30 seconds and multiply by 2 to obtain the leakage rate of the valve within one minute.
