Observe the state of the hydraulic device by side test

It is the most frequently used method to analyze the status of hydraulic equipment by means of sensory observation or simple testing method. The method of judging the condition of hydraulic devices is introduced with examples.

1. use the senses to determine the condition of the hydraulic gear directly

This method is the most simple, but relatively crude, suitable for preliminary evaluation of the problem, it relies on fault analysis personnel, rich field experience and keen observation.

The sense of the state of the hydraulic device can be determined directly from the following aspects.

1) vision. To observe the status of all kinds of instrument instructions, the execution speed and speed components, actuator motion coherence and coordination, all kinds of operation control device installation and connection of all the work indicator and the fault indicator, connection status of control wires, attracting all kinds of electrical, hydraulic oil, oil vapor bubble, color and turbidity degree etc..

2) hearing. To determine if the hydraulic pump power output, whether there is cavitation, hydraulic pump and motor bearings are damaged, the pump or motor is dry friction, whether there is leakage within the system, the electromagnet is attracted or so loose, machine installation is reliable, the existence of hydraulic shock and gun phenomenon, in addition, can also monitor alarm.

3) tactile sensation. The utility model is used for investigating the temperature rise of a hydraulic element surface, and by touching the outer wall of a hydraulic element or a hydraulic pipeline, the utility model can also judge whether there is oil flow and whether the flowing oil has higher pressure.

4) smell. It is mainly used to judge whether the motor, electric appliance coil and electromagnet are burned out, whether the hydraulic oil is bad or not.

2. test and determine the status of the hydraulic gear with a pressure gauge

Pressure is the most important parameter of hydraulic device. It is very sensitive to the variation of hydraulic equipment, and it is the most common fault detection method to judge the state of the system by measuring the pressure of the relevant parts of the system. In this way, the range and accuracy of the pressure gauge should be selected correctly, and the measuring point that can accurately reflect the status of the component is selected. First in the equipment under normal condition, the measured normal pressure value, and on this basis, according to the working principle of the hydraulic system, after that the related component wear, relevant points of pressure value of what changes will occur, thus determine the damage element. As an example, the method of measuring hydraulic device with pressure gauge and judging its failure state is briefly introduced.

Hydraulic circuit as shown in Figure 5-1, the diameter of 63.5mm, the pressure of 13MPa, the use of proportional directional control valve swing cylinder two kinds of speed (first, fast, slow). It can be seen from the figure, 1 times over the 4 element element circuit pressure maintained at 13Mpa, in order to avoid the hydraulic shock, element 6 guarantee swing cylinder at any position to stop, 2 components superimposed on the element 3 to 3 components provide the working pressure of 5Mpa, the oil valve element 8 Taiwan and pumping element 9 to separate loop storage hydraulic energy and nitrogen pressure is 8Mpa.

The pressure gauge with range 0~15MPa and scale O.1MPa is used to measure the pressure of A-I at 9 pressure points when the loop is not working. The nitrogen charging pressure and J value of accumulator are measured by means of nitrogen charging tool. The results are shown in table 5-1.

These data are saved as the original data of the hydraulic circuit, and the performance of the hydraulic components in the loop can be determined after checking and comparing monthly.

1 filter. You can see from the table, G and H point pressure is 0.1Mpa, this is the pipe pressure loss, filter and valve, when the pressure dropped to 12.75Mpa H or below, the filter is dirty should be replaced.

2) balance valve. When the pressure of the F, E and I points is the middle of the table, the sealing performance of the balancing valve is good, and the control part of the pressure compensator is internally discharged.

3) pressure compensator. When the pressure difference between the A point and the I point is less than 1.7Mpa in the meter, the control part of the pressure compensator is discharged.

4) proportional directional valve. C and D respectively in the two end connecting pipe proportional valve main valve on the valve core pilot proportional solenoid pilot valve zero characteristic is good, good heart opening is C, D is zero, otherwise drift or heart valve opening degree difference, should consider replacing the pilot part or zero.

5) accumulator. After the pressure oil of the accumulator is unloaded, the nitrogen charging pressure is measured at 10min below the 8MPa, and the pressure is zero if the accumulator bladder is damaged or the pressure head (nitrogen inlet) is leaking.

6) stop valve. The valve is in the closed position, and put the oil in the G-spot, using pressure gauge pressure, 10min pressure is rising. See, if the valve inner leakage.

3. test and determine the status of hydraulic devices with a flow meter

The flow rate is also an important parameter of the hydraulic device. The flow meter can accurately measure the internal leakage and volume efficiency of the hydraulic components, and the flow meter can also conveniently detect the blockage of the hydraulic circuit. In the production field, the ordinary LC elliptic gear flowmeter can be used to obtain sufficient accuracy. Therefore, an example of judging the damage of hydraulic components with a flow meter is presented.

The hydraulic circuit is shown in figure 5-2. Firstly, the flow and leakage of the components are measured in the normal state, which is the standard for judging the future failure.

1) field direct inspection. The hydraulic system of a Za is shown in Figure 5, the test tool for the stopwatch, drums, scales, the detection method is that the hydraulic cylinder at the bottom or top dead position, while the oil return pipe of a relief valve connected to the tank outside the cartilage rubber barrel, then the overflow valve pressure to the rated pressure, start the pump motor it can be used to measure the rated pressure of the flow of ma. The rubber pipe is connected to the reversing valve return pipe, and the inner reversing valve and the hydraulic cylinder can also be detected.

2) tester test. Figure 5-2B shows the pump barrier bypass test. Figure 3 as tester, which is composed of a flow meter, control valve, pressure gauge, temperature indicator and other components of the portable instrument, small volume, convenient installation. The tester return pipe tied to the tank, the pump and the system separates control and protection no longer subject to overflow valve, open the control valve tester, start the motor (or engine) to operate at rated speed, which will force respectively to nine and no-load pressure rated pressure can be measured by no-load flow and o the rated flow of ma.

4. determine the system status by testing the speed or rotation of the actuator

The change of movement speed or speed of actuating element is the reflection of structural state change of some components in hydraulic system. The fault status of the hydraulic system can be concretely judged by examining the changes of the speed or the rotation speed of the actuator and adding some other information. For example, the hydraulic motor speed drops, if the hydraulic motor of leaking oil pipe leakage increases, indicating symptoms caused by hydraulic motor leakage, if leakage increases the leak of the hydraulic pump, the pump is damaged and cause symptoms. Hydraulic cylinder running speed can be measured by stopwatch, in a certain length of running time to find out, hydraulic motor speed can be measured by tachometer. If there is no tachometer, when the speed is not too high (less than 100r/min). It can be marked on rotating parts and directly read the speed per minute.

Investigation of the actuator speed or speed, also in the equipment when measured speed or speed value after baseline fault judgment. The test process must pay attention to adjust the pressure, adjust the flow and system load and other factors consistent.

5. determine the component status by testing the surface temperature of the quick pressure component

1) the side test and judgement of the temperature of the hydraulic component, the overflow of the surface of the hydraulic component is determined by its internal heat generation and divergence. Hydraulic components itself overheating, causing surface temperature rise, there are two main situations, one is throttling heating, one is friction heating; the two cases are connected with the components damaged. Directly test the surface temperature of a component with a thermometer, and infer the change of its internal state. Under normal conditions, the hydraulic components are listed at temperatures below 50 degrees Celsius, and when faults occur, the temperature can rise to over 80 degrees celsius.

The surface temperature of the hydraulic component can be measured by contact thermometer or by a simple method, that is, the ordinary glass tube thermometer is wrapped with rubber and attached to the surface of the measuring point. Test and analysis of the surface temperature of hydraulic components is still to measure the standard temperature under normal conditions. The temperature and load conditions, as well as the cooling conditions, must be taken care of in the testing process. The test shall be carried out when the equipment is in normal operation and the temperature reaches equilibrium.

(2) hydraulic component infrared temperature monitoring and F-strong aircraft hydraulic temperature test example of temperature is one of the important characteristic parameters of hydraulic device status evaluation, using infrared detector temperature monitoring of hydraulic system, important information can be obtained and the change of state. The infrared detector is easy to operate and high sensitivity, which is advantageous to diagnose the hydraulic faults accurately in the field.

Such as the F-strong aircraft hydraulic system is used for the landing gear and flaps, reduced with plate and nozzle, and used to assist the manipulation of the ailerons and tail, it consists of hundreds of components and tubing, once the failure will lead to loss of control, the serious consequences of the plane crash. Typical faults are:

1) dry friction of hydraulic pump. When cavitation occurs in the hydraulic pump, dry friction occurs between the rotor and the valve plate, and the heat generation is caused by the friction heat, so that the temperature of the pump body is increased.

2) oil filter dirty. In the process of oil circulation, impurities accumulate on the filter core, so that the filter gap becomes smaller and the energy loss increases, which causes the temperature rise of the oil filter housing.

3) leakage within components. When the internal clearance of the component increases or the seal is damaged, the inner leakage causes throttling heat, which leads to the rise of the element shell temperature.

4) the components are blocked internally. If the throttling hole in the throttling device is blocked by impurities, the throttling device does not work, the flow rate is reduced to zero, and the temperature of the element shell is lowered.

The infrared detector can monitor the faults of the hydraulic system. The infrared detector of an aircraft hydraulic system is shown in figure 5-3.

The basic method of infrared detector monitoring Yi machine hydraulic system is related to the temperature measuring point; measure the normal state and all kinds of typical fault value as the standard value. Then the temperature test results are compared with the values in the standard state to determine their status. For example, for systems shown in Figure 5-4, a set of data can be measured in normal circumstances, then a fault (throttling off the throttle, blocking analog), and a set of data are measured, as shown in table 5-2.

As can be seen from the table, when the restrictor is blocked, the temperature of the safety valve is greatly increased, while the temperature of the restrictor is greatly decreased. The reason is that the throttling device has no liquid flow, and can not play throttling action, and has no throttling heat, so the temperature drops. As the restrictor is blocked, the relief valve is switched on, where the energy loss is converted to heat, causing the element temperature to rise.