Failure Causes and Test Methods of Agricultural Machinery Pressure Valves

In the hydraulic system of agricultural machinery, the pressure valve is a kind of component with more applications. The sudden failure of the pressure valve will directly affect the normal operation of the machinery and equipment. This article divides the cause of the failure of the pressure valve and gives an example to introduce the test method of the pressure valve. 1. Common causes of failure (1) Hydraulic spool and valve body constantly wear and tear in use, making the parts size, shape and surface quality changes. (2) Balance spring, valve core and valve seat in the hydraulic valve work under variable load for a long time, resulting in fatigue and cracks, causing the spring, broken valve seat sealing surface flaking and damage. (3) The remaining residual stress in the process of hydraulic valve parts processing and the external load stress in the process of using, exceeding the yield strength of the part material, the parts are deformed. (4) hydraulic oil mixed with excessive water or acidic substances, the use of a long time, the corrosion of parts in the hydraulic valve, so that it should lose the accuracy. (5) unbalanced radial force between the valve core and the valve sleeve, and finally the valve core is pressed against the inner wall of the valve sleeve to be jammed. (6) When the hydraulic valve is manufactured or repaired, the specified technical requirements are not met; or the parts are not kept in good condition, rust occurs, dirt is mixed in, and the like. 2. Examples of test methods Pressure relief valve, relief valve and sequence valve, etc., this article to illustrate the pressure relief valve test items and test methods. Pressure valve test can be carried out on a dedicated test bench, but also in a comprehensive test bench. (1) pressure regulating range and pressure stability test. Adjust the test valve adjustment hand wheel, from full open to fully closed, and then to fully open, from the pressure gauge to see the pressure rise and fall as well as the pressure regulating range. Pressure gauge pointer should be steady rise and fall, pressure regulating range should meet the provisions of the pressure regulating range, the maximum pressure, the pressure pulsation value shall not exceed the specified value. (2) the amount of leakage test. Adjust the hand wheel is adjusted by the valve to the fully closed position, adjust the overflow relief valve to be the highest pressure of the valve under test, and then adjust the test valve adjustment hand wheel, so that the test valve overflow leakage measurement. (3) Unloading pressure test. The remote control port of the relief valve connected to the tank so that the test valve through the test flow, measuring the pressure relief valve inlet and outlet pressure, the difference is the test valve unloading pressure. (4) pressure loss test. Adjust the test valve adjustment hand wheel to completely loosen, and make the test valve through the test flow, pressure gauges measure the inlet and outlet port pressure relief valve, the difference is the pressure loss of the valve under test. (5) opening and closing characteristics of the test. Close the overflow relief valve, adjust the tested valve to the maximum pressure, adjust the overflow relief valve to depressurize the system gradually, and measure the overflow volume of the tested valve when it drops to the closed pressure of the tested valve. Adjust the overflow relief valve, the test valve does not overflow began to make the system gradually boost pressure, when it rose to the test valve opening pressure, measured by the valve overflow.

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Dry weather is the "culprit" of cold

"The child has been suffering from a cold for more than two weeks. He has a fever and a runny nose. At first, I thought he had a common cold, so I went to the nearby clinic to buy medicine, but it didn't work. Now the child not only coughs, but also has blisters on his mouth and nosebleeds at night. This year has passed without much comfort..." at a maternal and child health care hospital in Chaoyang District, Beijing, The child's parents, Ms. Zhao, said in distress.

According to the pediatrician of the hospital, there is a high incidence of respiratory diseases in children this winter. The main reason is that the weather is dry this year, there is no snow, and there are many bacteria and dust in the air. From the reception situation, the patients are basically mycoplasma infection or chlamydia infection, including many cross infections.

Zhang Xingchao, deputy director of internal medicine of Beijing hospital, introduced that due to the low air humidity, the influenza virus propagates faster in a dry environment and survives on floating dust, which will accelerate the spread of cold. However, due to the failure of "wet deposition", it will also cause serious urban air pollution and easily lead to respiratory diseases such as asthma and pneumonia.

The medical staff of the cardiovascular department of Beijing Municipal People's hospital told reporters that since the beginning of winter, there has been a long drought without rain (snow), the weather is warm and dry, and people's life is irregular during the Spring Festival, resulting in changes in human physiological functions, slow blood flow speed and increased blood viscosity. Middle-aged and elderly patients with hypertension and hyperlipidemia are prone to cerebrovascular spasm, coronary heart disease and other diseases. These diseases have strong concealment, sometimes come quickly and seriously, and are easy to lead to sudden death. Before and after the Spring Festival, the number of middle-aged and elderly patients with cardiovascular disease increased abnormally, especially the elderly over 65 years old.

Wang, director of cardiovascular department of Beijing Municipal People's Hospital, reminded that in the current extremely warm and dry weather environment, the effective way to prevent cardiovascular disease is to drink more water, eat less meat, exercise more and keep warm. Especially the middle-aged and elderly people with "three high" should pay special attention

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