Un proyecto precedente: teleducaciön en las aulas

Some of the gases used in the laboratory are held in cylinders (steel cylindrical vessels with a spherical bottom and a narrowed upper part, in which the locking valve is screwed in. To prevent the valve damage, on the upper part of the cylinder is put an iron cap. The lower part of the cylinder has a welded stand ("shoe"), which allows the cylinder to be kept upright (Fig. 1.26).

1. Protective cap, 2. Cylinder valve, 3. Underlay rings, 4. Passport data Figure 1.26 – Cylinder construction

Cylinders intended for gases storing (Сl2, NH3, SO2 etc.), which are

liquefy under the pressure. They have an internal tube, which goes from the shut-off valve to the bottom of the cylinder. It is recommended to use such cylinders inverted, in order to the end of the tube is out of the liquid. In this case, the possible release of liquid gas from the valve is eliminated. Locking valves are made of bronze or steel. Their case is screwed into the upper part of the cylinder.

For prevention the false filling of cylinders by other gases, provided the distinctive coloring and marking of cylinders (Table 1.5).

In cylinders that contain liquefied gas, regardless of the amount of fluid in the cylinder, the pressure gage shows the vapor pressure. Cylinders with acetylene are filled with porous mass (pumice, coal), impregnated with

acetylene solution in acetone. For cylinders with oxygen used reducer, which do not contain layer of organic material. Lubricate parts of an oxygen reducer with any oil, as well as to put on the output nozzle rubber and other hoses from organic materials, except fluoroplasts, is strictly prohibited. In an oxygen stream, it may become inflamed, causing a cylinder explosion.

Table 1.5 – Recognition of industrial cylinders with compressed gases [2]

Gas Dyeing of cylinder Colors of the

inscription Pressure, atm

Possible impurities N2 NH3 H2C2 H2 SO2 CO2 O2 CH4 Cl2 Black Dark yellow White Dark green Black Black Light blue Red Green Yellow Black Red Red White Yellow Black White Blue 150 30 (liquid) 15…20(in acetone) 150 6 (liquid) 125 (liquid) 150 150 30 (liquid) O2, Ar, Ne, He H2O, CO2, H2, N2 H2O, O2, N2, (CH3)2CO N2, O2, CO, CO2, CH4, H2S H2O, O2, N2, CO2 O2, N2, H2O, CO, SO2, H2S H2, N2, Ar, CO2, H2O N2, CO2, H2O O2, N2, HCl, CCl2O, CO2 Valves, reducer and pressure gages for cylinders with acetylene and ammonia are made only with steel. All locking devices containing copper (bronze, brass) should not be used at work with ammonia and acetylene because of their interaction with copper.

The cylinders are kept upright in special racks or attached to the wall or laboratory table with iron clips. The cylinders should be located far away from heating batteries, any heating devices and electric shields. They should also be protected from direct sunlight.

The cylinders are intended for storage, transportation and usage of compressed (nitrogen, air, oxygen, hydrogen sulfide), liquefied (ammonia, sulfur oxide (IV), butane) or dissolved (acetylene) gases at a pressure higher than 0,07 MPa.

– necessary mechanical strength of cylinders and proper control of their condition;

– preventing false filling of cylinders by other gases (for example, cylinders for noncombustible gases – combustible, gas cylinders – oxygen);

– compliance with the rules of filling, transportation, storage and use of cylinders;

– preventing the false filling of cylinders by other gases (for example, cylinders for noncombustible gases – by combustible, cylinders for combustible gases – by oxygen).

The required mechanical strength of the cylinders is ensured by their high-quality fabrication and periodic inspection. Cylinders for compressed, liquefied and dissolved gases are welded (working pressure in a cylinder up to 3 MPa) or seamless.

During operation, cylinders are tested, which include: an overview of the internal (if possible) and external surfaces of cylinders; weight and strength check; hydraulic test. The inspection of cylinders is carried out in order to detect corrosion, cracks, dents and other damages on their walls to determine the suitability of cylinders for further operation. If the results of the survey are unsatisfactory (cracks, dents, depths of more than 10% of the nominal wall thickness are found), then the cylinders are discarded.

The value of the test pressure and the time of the endurance of the cylinders under such pressure shall be determined by the relevant standards (for standard cylinders) and the technical conditions (for non-standard ones), with the test pressure being not less than one and a half of the working pressure.

Exceptions to the general rules of attestation apply to cylinders with acetylene – a flammable gas widely used in the industry for welding and cutting metal constructions. Due to the high explosive hazard of acetylene, it is

stored in dissolved form in cylinders filled with porous mass impregnated with acetone. With periodic verification, the porous mass is not removed, and instead of the hydraulic test, the test with nitrogen is carried out. In this case, the cylinder is lowered to water at a depth of at least 1 m. The state of porous mass in cylinders for acetylene should be checked at least one times every 24 months.

The certification of cylinders is carried out by enterprises, filling- stations and test points, which, in accordance with the established procedure, have received permission for this in the special bodies licensed for verification and certification of cylinders.). After verification, the stamp is placed on the upper spherical part of the cylinder and the date of the next certification is indicated.

In addition, the side valves of gas cylinders filled with combustible gases have a left-hand thread, and cylinders filled with oxygen and other non- combustible gases are right-hand.

The operation, transportation and storage of cylinders at the enterprise must be carried out in accordance with the requirements of the instruction approved in accordance with the established procedure. Workers that serving cylinders must be trained and instructed in accordance with current regulatory documentation. The residual gas pressure in the cylinder must be at least 0,05 MPa.

The main device that provides safety during operation of cylinders is a reducer that reduces the pressure of compressed gas to the working. By design, the reducers can be different (one and two-chamber, direct and indirect), but in all reducer, the low-pressure chamber should have a pressure gage and a spring safety valve, adjusted to the appropriate permissible pressure.

Gas cylinders are stored in special rooms (warehouses) or under eaves that protect them from atmospheric precipitation and sunlight. It is prohibited

to keep cylinders with oxygen and flammable gas in one room. Cylinders with poisonous gases are stored in special enclosed spaces. Storage for cylinders with explosive and fire gases must be in the lightning protection zone.

Filled cylinders are kept upright in specially equipped nests, cages or fenced barriers to prevent them from falling. Gas cylinders must be at least 1m away from radiators and other heating appliances and not less than 5m from the sources of open flame. Oxygen cylinders need to be protected from contamination by any lubricant or fat, as they can form an explosive mixture with pure oxygen.

1.4.4 EXAMPLES OF SOME SUBSTANCES CLASSIFICATION IN APPLIED