Using Oil Pressure Meter Skillfully to Diagnose Faults of Hydraulic System

Hydraulic pressure gauge can be used to diagnose hydraulic system faults. For example, by detecting the pressure value of hydraulic system and observing the law of pressure change of hydraulic system, the technical status of hydraulic system and components can be understood. Then according to experience analysis and judgment, it is possible to find out the cause of the failure, and then formulate the maintenance plan.

(1) Mechanical Hydraulic Meter Mechanical hydraulic pressure gauge is the simplest tool to detect the pressure of hydraulic system. It has a curved hollow spring tube, pull rod, rack, gear, pointer and buffer mechanism. When testing the pressure of the hydraulic system, the pressure oil enters the hollow spring tube, which deforms the spring tube. The gear rotates through the pull rod and rack, and the gear drives the pointer to rotate. Thus, the oil pressure is converted into the pointer rotation, and the pressure value of the detected part of the hydraulic system is displayed. If the oil pressure at the detected position is pulsating, the indicator of the oil pressure gauge will fluctuate with the pulsation.

Mechanical hydraulic pressure gauge is divided into anti-vibration hydraulic pressure gauge and anti-vibration hydraulic pressure gauge. The spiral spring tube of anti-vibration hydraulic pressure gauge and the case are filled with high viscous mineral silicone oil, which can play a damping role. It can reduce the vibration and anti-vibration of the pointer, so the dynamic response of the anti-vibration hydraulic pressure gauge is poor. The anti-vibration hydraulic pressure gauge is more suitable for dynamic detection of the pressure of hydraulic system.

When testing oil pressure by mechanical pressure gauge, it should be in a vertical state, and the line of sight is vertical to the dial, so that the accurate pressure value can be seen.

(2) Digital Display Hydraulic Meter Digital hydraulic pressure gauge, with built-in pressure sensor, is a hydraulic pressure gauge which integrates pressure detection and display. It has good pressure impact resistance and high display accuracy. The maximum value detected can stay on the display disk, and has a key clearing function.

In the process of detecting the pressure rise of hydraulic system, the digital display of the hydraulic pressure gauge changes continuously in an instant. Maintenance personnel can not observe the change process of pressure from low to high, but can only see the maximum pressure. If the pressure of the hydraulic system under test has pulsation, the digital display value will change continuously in an instant, and it is difficult to observe the amplitude of the fluctuation.

(3) Multipurpose Hydraulic Meter The universal hydraulic pressure gauge is composed of pressure sensor, flow sensor, temperature sensor, computer and cable, and it is the best tool for detecting hydraulic system. The multipurpose hydraulic pressure gauge can display the pressure change curve of the hydraulic system through the computer screen, and record the corresponding relationship curve of pressure, flow rate and temperature. The drawings are a set of universal hydraulic pressure gauges. The display screen of hand-held universal hydraulic pressure gauges in the drawings shows and records the pressure change curve of a hydraulic pump.

In selecting mechanical hydraulic pressure gauge to test hydraulic system, technical requirements such as accuracy grade, selection points and testing environment need to be considered, while digital display hydraulic pressure gauge and universal hydraulic pressure gauge need not consider the above technical requirements.

(1) Accuracy level Experience shows that the hydraulic gauges made in Germany are the most accurate, reliable and durable. The unit of measurement of German oil pressure gauge is bar. The unit of measurement of oil pressure gauge produced according to national standard in our country is MPa. 1 bar is equal to 0.1 MPa. It should be converted when used.

German standard stipulates that the accuracy of oil pressure gauge can be divided into A (+0.5%), B (+1.5%) and C (+2.5%). The above accuracy levels are full range error values. The oil pressure gauge with a diameter of 60 mm is commonly used, and its accuracy level is C. For example, the pressure value detected by a C-level precision oil pressure gauge with a range of 60 MPa is 35 MPa, and calculated with C-level accuracy, the error of the pressure value is 0.875 MPa. It can be seen that the actual error of the oil pressure gauge is not only related to the accuracy level, but also to the range of the oil pressure gauge and the measured pressure value.

(2) Main points of selection In order to ensure the detection accuracy, when using more than two hydraulic pressure gauges to detect the pressure value in the same hydraulic system, the same manufacturer, the same brand, the same precision grade, the same range and the same time out-of-factory oil pressure gauges should be selected, and the silicone oil filling degree in the shell of the anti-vibration oil pressure gauge should be the same.

When choosing an oil pressure gauge, its measuring range should be within the range of the tested pressure. The smaller the range of the Hydraulic Gauge is, the higher the accuracy and the smaller the error are. Therefore, the selection of oil pressure gauges with a range greater than 25% of the measured value is conducive to reducing the range error.

(3) Detection environment Vibration-resistant oil pressure gauge has certain requirements on the use temperature. When the temperature reaches zero, it is not suitable to use. When testing oil pressure in special environments such as low temperature, high temperature, long distance from the testing end to the oil pressure gauge or violent vibration, the detection accuracy of the vibration-resistant oil pressure gauge will be affected.

Preparations before pressure measurement

No matter which kind of hydraulic pressure gauge is chosen to test the hydraulic system, the following four preparations should be made before testing:

Firstly, it is to understand the working condition, characteristics and load characteristics of the tested hydraulic system.

Secondly, it is necessary to check the hydraulic system diagram of the tested machinery, to determine the detection point by checking the operation data of the executing elements under normal conditions.

Thirdly, according to the test data of the hydraulic system to be tested, prepare the hydraulic pressure gauge, the pressure measuring joint connected with the test point, the three-way connection in series, and the recording paper, pen, stopwatch and so on. If necessary, prepare the video equipment for playback of the test process.

Fourth, prepare for safety. Oil pressure gauge should have protective device.

When measuring the pressure of the hydraulic system in the rising stage, the rising process of the system pressure will be observed from low to high. This is because there is a certain volume inside the actuator of the hydraulic system, and the rising time of the pressure will be different when the flow and load of the hydraulic system are different.

In the pressure maintenance stage, the hydraulic pressure gauge keeps stable after rising from zero to the highest pressure of the system in the predetermined time, which indicates that the hydraulic system works steadily and reliably. If the pointer flutter and jitter, it indicates that the hydraulic system is unstable; if the jitter amplitude is too large, it indicates that the hydraulic system has pulsation phenomenon. The pointer jitter of the hydraulic pressure gauge may be the fault of the hydraulic pump, the suction of the oil intake pipe, and the leakage of the hydraulic system.

When the hydraulic system reaches the maximum load in the stage of load overflow, the indicator of the hydraulic pressure gauge should indicate the overflow pressure instantaneously. If it does not reach the overflow pressure, the indicator stops, or first rises from low pressure to medium pressure, then suddenly jumps to the overflow pressure after stopping, indicating that the overflow valve and pressure limiting valve are unstable or malfunctioning.

(2) Universal Hydraulic Pressure Meter

Pressure, temperature and flow data of hydraulic system can be detected by universal hydraulic pressure gauge. Pressure sensor or temperature sensor of corresponding range should be installed at preset pressure measuring point of hydraulic system before measurement. Flow meter should be put into pipeline when detecting flow. These sensors are connected with the universal hydraulic pressure gauge by cable, and the signal value detected by the sensor is transmitted to the universal hydraulic pressure gauge computer with the functions of storage, display and microprocessing. The detection curve can be viewed and analyzed repeatedly, and the data can be stored. The inspector can judge the fault logic by combining mechanical or electronic hydraulic pressure gauge, and preliminarily determine the location and cause of the fault of the hydraulic system.