What is the principle of checking the air tightness of the device, and what is the principle of chec

The principle of air tightness test is to first let the device and the attached liquid (generally refer to water) form a closed whole, change the temperature of the whole, resulting in a change in pressure, to judge the air tightness, due to the different devices, the inspection method is also different.

This is a test method in which compressed air (or ammonia, freon, helium, halogen gas, etc.) is pressed into a container and the pressure difference between the inside and outside of the container is used to check for leaks.

The air tightness test requires the air tightness tester, which is specially used to test the tightness of cavity mechanical products. It is mainly used in the production of automobile engines, gearboxes, axles, water tanks, fuel tanks, etc., which have sealing requirements for the cavity. The air tightness detector adopts the intelligent design of embedded control, which can automatically complete the test procedure and automatically judge the inspection results.

1. Elevated temperature method.

Increasing the temperature of the gas in the gas generator system can temporarily increase its pressure, so that this integral part of the air escapes (bubbles can be observed at the liquid), and when the temperature returns to the initial temperature, this overall pressure decreases, causing a section of water column to be sucked in the air duct immersed in water.

2. Liquid level difference method.

Clamp the rubber conduit part with an air stop clip, add water to the long neck funnel, immerse the lower end in water, continue to add water to form a water column, produce a height difference, and the water column does not fall back for a period of time, indicating that the air tightness is good.

The principle of testing the air tightness of the device is usually based on the principle of thermal expansion and contraction of gas.

During the experiment, when the volume of gas is heated and expanded, if the airtightness of the device is good, the gas can only escape from the catheter and produce bubbles;

The temperature decreases, the volume of the gas decreases, and water will enter the catheter There are two general ways to check the tightness of the air:

First, when the outlet of the gas generating device is one, the principle of thermal expansion and cold contraction of the air in the device can be used;

Second, when there are two outlets of the gas generating device, we must try to block one first, and then check the quality of its air tightness.

The principle of air tightness is whether there is air leakage when the inner wall of the closed object is pressurized.

If the airtightness of the welded parts is checked, flaw detection is also possible.

It is impossible to exist in a completely closed state in reality, depending on the permissible deviation of the stomata.

Yes. If the device is airtight, hold the test tube in your hand and there are bubbles coming out from underneath, and if you release your hand, a water column will form in the catheter and will not fall, and if the device is not airtight, there will be no water column.

Answer: Analysis:

When the gas volume is heated and expanded, if the air tightness of the device is good, the gas can only escape from the conduit and produce bubbles; The temperature decreases, the volume of the gas decreases, and water enters the catheter

One. After assembling the experimental instrument, put one end of the catheter into the water and heat the test tube, if after a while, there are continuous bubbles coming out of the catheter mouth, indicating that the device is airtight. If there is no above phenomenon, the air tightness is not good, and it is necessary to carefully use the above method to test it piece by piece.

Two. Put one end of the catheter in the water and cover the tube with your hand for a while, if there are continuous bubbles coming out of the catheter orifice, the air tightness is good.

Three. Put one end of the catheter into the water, if the other end of the catheter is inserted into the assembly instrument, when the front of the connected instrument is an empty reaction bottle with a jack, first use the separating funnel to add half a bottle of water to the bottle, insert the lower end of the separating funnel below the liquid level, and then add water dropwise. If the liquid level in the bottle rises, the air tightness is not good.

Summary: The first two methods use the characteristics of thermal expansion and cold contraction, and the third method uses the pressure, and the air tightness of the general inspection device is considered from these two factors.

1. Air thermal expansion and cold contraction method.

This is a commonly used method introduced in the textbook, the operation is simple, the end of the air duct is inserted into the water tank, hold the test tube with your hand or use an alcohol lamp to heat it slightly, so that the gas in the test tube is slid and pure thermal expansion, and there will be bubbles at the end of the air duct. When the hand is released or the alcohol lamp is withdrawn, a section of water rises at the end of the air duct, which proves that the device is airtight and does not leak.

Second, the water injection method.

Suitable for inspecting a Energizer or a device similar to a Energizer. First of all, let the mill close the exhaust pipe, inject water from the top funnel mouth, and then fill water when the lower end of the funnel is closed by water, and the water surface does not fall, indicating that the device has good air tightness; If the water surface drops, it indicates that the airtightness of the device is poor.