14、 Whether there is residual pressure (gas) in the cylinder, and whether the residual gas is consistent with the gas to be filled.

 

The residual pressure (gas) and gas quality in the bottle should be checked when the bottle temperature is close to the ambient temperature. Because the bottle temperature is too low, especially in winter, it is difficult to measure the pressure and sample for analysis. If the residual pressure in the cylinder is lower than the specified value, the cylinder may be wrongly judged as empty because the pressure cannot be measured.

When the temperature difference in the room is greater than 30 ℃, in order to facilitate the inspection of residual pressure and sampling analysis, the cylinder shall be moved to the room for standing for 4 hours (dissolved acetylene cylinder for 8 hours) before pressure and sampling analysis.

Check the residual pressure. In general, the following items can be judged:

（1） A certain pressure in the bottle indicates that the bottle valve has been closed before the gas in the bottle is used up, and the bottle is not used for other purposes.

（2） There is residual pressure in the bottle, and foreign matters are not easy to enter the bottle.

（3） There is considerable residual pressure in the bottle, so it is unnecessary to replace or vacuum the bottle before filling.

（4） For dissolved acetylene cylinders, the reset solubility of acetylene under different residual pressures and ambient temperatures can also be checked according to the residual pressure and the ambient temperature at which the residual pressure is measured.

Check the residual pressure. For experienced inspectors, the residual pressure in the bottle is usually determined by the speed and sound of the air flow after the bottle valve is opened. This practice is conducive to improving the inspection speed. Beginners should learn from this inspection experience.

If there are special requirements for residual pressure inspection, special pressure gauge must be used for measurement. For example, for dissolved acetylene cylinders, the residual pressure in the cylinder must be measured with a pressure gauge, and when it is specified that the residual pressure is less than a certain requirement, the purity of the residual gas in the cylinder must be analyzed. When the purity is lower than 98%, the cylinder needs to be vacuumed and replaced.

Before the residual pressure is measured and the pressure gauge is connected, the bottle valve shall be slightly opened to purge for 1-2 times, and the impurities falling into the valve shall be blown out.

When checking the residual pressure, if it is found that the pressure in the permanent gas cylinder is 1/2 higher than the inflation pressure, or the volume of liquefied gas and dissolved acetylene cylinders is 1/2 higher than the filling volume, they should be marked and returned to the user.

The terms "residual pressure" and "residual gas" have no meaning of how much pressure and how much gas remains. One bottle is filled with 150kgf/cm ² (14.7MPa) pressure, 6m ³ Oxygen cylinder, use 145kgf/cm ² (14.2MPa) pressure, 5.8m ³ Oxygen, 5kgf/cm left in the bottle ² (0.49MPa) pressure, 0.2m ³ Oxygen is called residual pressure and residual gas; 25kgf/cm is used ² (2.45MPa) pressure, 1m ³ Oxygen, 125kgf/cm left in the bottle ² (12.25MPa)、5m ³ Oxygen is also called residual pressure and residual gas. Therefore, it cannot be understood as "no more pressure, no more than one or two pressures" and "no more gas, no more than 100 liters" without paying attention to safety protection. Any "full bottle" sent by the user by mistake when checking "empty bottle"

When opening the bottle valve to check the residual pressure and gas quality, the person shall stand at the side of the side nozzle of the bottle valve, and shall not stand at the opposite or back of the side nozzle. The face shall also not face the top of the bottle valve, in order to prevent injuries caused by the airflow from the side nozzle and the particles and sundries carried by it, or by the gas cylinder pushed by the reverse force of the airflow, or by the handle, shaft valve and hexagonal sealing cap that are tripped and flying.

In recent years, gas cylinders in some cities have been replaced by fixed caps, and the valve handles have been correspondingly changed from no makeup to hexagonal. Due to certain structural defects of the hexagonal cap, when the cylinder valve is opened and the hexagonal handle is rotated, the cylinder valve sealing cap often rotates with the hexagonal handle at the same time. After tripping, the coaxial valve and the hexagonal handle are hit by the gas in the cylinder, which is very easy to hurt people or cause other accidents.

The hardness of the valve shaft of the acetylene cylinder valve in use is not enough. After a period of use, the four straight edges and corners on the top of the valve shaft are twisted into spiral edges. If the spiral rib is stuck on the shaft hole of the sealing cap valve, the sealing cap will rotate with the shaft valve at the same time when the bottle valve is opened, so that the tripping will pop out. This is also the safety precautions when opening the bottle valve.

For cylinders with new cylinder valves, check whether the sealing caps are tightened before opening the cylinder valves. If it is found that the sealing cap is not tightened, it should be tightened to prevent the accident caused by gas leakage or tripping when opening the bottle valve.

A special wrench shall be used to open and close the bottle valve. It is strictly prohibited to use chisels, hammers, pipe wrenches and other tools that are vulnerable to valve damage. The opening and closing bottle valves shall be operated slowly and not too quickly to avoid excessive friction heat. Open the bottle valve with pressure gauge (or pressure reducer) more slowly to prevent excessive compression heat from forming in the connecting pipe and pressure gauge (or pressure reducer). Both friction heat and compression heat may cause combustion of combustible gas and combustion supporting gas cylinder valves or explosion of pressure (pressure reducer), and even lead to cylinder explosion accidents. If you act too quickly, even if there is no combustion or explosion, you will damage the components, threads and gaskets of the cylinder valve.

When closing the bottle valve, it is required not to act too quickly, but also not to close it too tightly, because too tight closing will also damage the valve, thread and gasket, and may cause trouble and danger for the next opening and closing of the bottle valve.

The cylinder whose valve cannot be opened shall be transferred to the periodic inspection station for treatment. It is strictly prohibited to repair the cylinder valve at the inspection site without authorization.

If you find that there is no residual pressure (gas) in the cylinder after the valve is opened, you must be careful. You cannot identify an empty cylinder as an empty cylinder. You would rather treat an empty cylinder as a full one, rather than treat a full cylinder as an empty one, to prevent an accident from being masked by the possible illusion of an empty cylinder. In case of valve damage, stuck valve element or existence of rust residue, rust mud, sand, iron filings, ice and other sundries in the bottle, the bottle valve may not vent. If the cylinder is a "full cylinder" or a cylinder with a large residual pressure that is delivered by the user by mistake, it may be injured by the high-pressure air flow and its impurities if it is slightly negligent.

For cylinders with no residual gas discharged after the cylinder valve handle is opened, different treatment methods shall be adopted according to different types of cylinder valves. For diaphragm type and ball pressure membrane type bottle valves, ear washing rubber ball shall be used to absorb the gas in the bottle. If there is still no gas discharged, turn the cylinder valve handle back to the fully closed position, and then turn it back half a circle or one circle, gently tap the valve body with a hammer, or slightly stir the valve core from the side nozzle with a metal needle to listen for gas leakage. If there is still no gas leakage, raise the handle for another half circle or one circle, and then check according to the previous method.

During the above inspection, it must be noted that the human body should stand on the side of the nozzle at the side of the bottle valve to avoid the impact of high-pressure gas

Diaphragm and ball pressure diaphragm cylinder valves and other types of cylinder valves whose valve cores do not rise must be transferred to the periodic inspection station for gas cylinders.

Check the gas quality of the remaining gas in the bottle for two purposes: first, prevent combustible gas and combustion supporting gas from mixing into explosive detonation gas in the bottle; The second is to ensure that the purity of the gas in the bottle after filling meets the standard.

The best way to check the gas quality of the remaining gas in the bottle is to use instrument measurement and chemical analysis, which can be qualitative and quantitative, and can ensure both safety and gas purity meet the standard requirements. If residual gas with harmful impurity content exceeding 1/5~1/4 (volume) of its lower explosive limit is found when using instrument measurement or chemical analysis to check the gas quality, it is strictly prohibited to inflate the bottle, and it shall be handled according to the first requirement above.

After determination or analysis, it is confirmed that the remaining gas in the cylinder is the same as the gas to be filled, and does not contain any conflicting components. Only the cylinders whose purity does not meet the requirements, and the acetylene cylinders without remaining gas, should be replaced or vacuum treated.

At present, some bottled gas filling stations still use simple chemical reaction and flame characteristics to identify the remaining gas in the bottle. These two methods can only be used to determine the general nature of the residual gas. The methods are as follows:

（1）Gas cylinders for identification of chlorine, hydrogen chloride, phosphorus oxychloride, dichlorodimethylsilane and other gases shall be close to the nozzle at the valve side of the cylinder with a cloth or cotton ball soaked in ammonia. If white fog occurs, it is deemed as qualified. For gas cylinders for hydrogen arsenide, ammonia, phosphine and other gases, mercuric chloride test paper, red litmus paper, silver chloride and potassium iodide test paper soaked in water shall be used respectively, and close to the nozzle at the valve side of the cylinder. If the test paper changes color, it is deemed as qualified.

This kind of inspection needs an experienced person, otherwise it will also lead to wrong identification. For example, when identifying chlorine cylinders, if antimony trichloride, antimony pentachloride, chloroform, hydrofluoric acid, etc. are poured into the bottles, white fog will also be generated by using cloth or cotton balls soaked in ammonia.

（2） The remaining gas quality is identified by flame characteristics, which is only applicable to oxygen, hydrogen, nitrogen, air and argon, helium, krypton, xenon lamp rare gas and other gas cylinders that do not produce toxic gas when contacting open flames.

This method is to use ear washing rubber ball to take gas sample from the nozzle on the side of the bottle valve, and then blow it to the burning stick incense or coil incense to identify the nature of the remaining gas in the bottle with the flame characteristics. After the stick incense or coil incense touches the gas blown out by the ear washing rubber ball, it burns violently and presents a bright phenomenon, indicating that the remaining gas in the bottle is oxygen; The flame is red and emits a slight popping sound, indicating that the remaining gas in the bottle is combustible gas; The open fire of stick incense or incense sticks extinguishes when encountering gas, indicating that the remaining gas in the bottle is non combustible or non combustion supporting gas; The gas and fire meet and make a detonation sound, or the ear washing rubber ball pops out of the hand and bursts, indicating that the remaining gas in the bottle has formed explosive mixed gas.

Using this method to identify the gas quality of the remaining gas in the bottle will also lead to identification errors. For example, it is difficult to identify if the "oxygen cylinder" is filled with other combustion supporting gases instead of oxygen, or if the "hydrogen cylinder" is filled with other combustible gases instead of hydrogen, it is difficult to identify. Even if explosive gases are found through flame inspection, it is unknown what the other gas that forms explosive gases is, unless instrument or chemical analysis is used again. In China, the method of quickly detecting gas tube to determine the nature and quantity of gas can be adopted.

Using flame to identify the residual gas in the bottle has the following dangers:

（1） For the filling station of combustion supporting gas and combustible gas, the inspector often conducts flame inspection on site, which is very dangerous to the operator and the workshop. In case that the air in the working environment forms an explosive mixture with some gas, the space combustion explosion will occur in case of open fire.

（2） If there is a mistake in incense management, the naughty person may directly touch the nozzle on the side of the bottle valve with the lighted stick incense or the coil incense to play with fire. In case of combustible gas or explosive gas formed in the cylinder, it will burn, explode or even explode in case of open flame gas cylinder.

（3） Inspectors forget to wear gloves or hold the ear washing rubber ball improperly, which may cause pain or injury in case of explosive gas.

（4） Improper operation of ear washing rubber ball may identify combustible gas or explosive gas as non combustible gas or non explosive gas.

When checking the gas quality of the remaining gas in the bottle, it is found that the remaining gas in the bottle is explosive gas. The gas in the bottle must be carefully discharged and replaced with nitrogen or other industrial inert gas that does not conflict with the gas in the bottle. Then handle according to the requirements of the first and third items above, otherwise it is strictly prohibited to inflate.

The cylinder with residual pressure (gas) confirmed in the cylinder shall be handled according to the requirements of the third item above to prevent the cylinder from being used for other purposes.

It must be pointed out here that when preparing to check the residual pressure (gas), it is strictly forbidden to check the residual pressure in the bottle or take samples for analysis if a special type of bottle valve is found before its structure and opening/closing method are clarified.