The device and principle of operation of gas transmission systems.
Combustible gases in question, almost all are chemical compounds of hydrocarbons. The most common natural gases are propane and methane.
We have one goal with you: to understand how the systems and mechanisms for the preloading, stopping and twisting of gas meters for household class work. Therefore, only the low pressure natural gas transmission system will be considered (to be reduced, we will call it as LNG).
To regulate the flow of natural gas through LNG, cork taps are mainly used. Such taps are very reliable, because during operation, all parts are constantly rubbed together, ensuring constant reliable tightness of the device, in general.
These taps consist of a casing inside which a special cone-shaped nest is made, as well as openings for the entrance and exit of natural gas. A cone-shaped flap is installed in the cone-shaped socket. The valve has a special through hole, through which natural gas will pass. The cone-shaped flap tightly pressed against the walls of the cone-shaped nest with a special spring. The spring pressure on the damper is regulated by a special bolt-stopper. Spring and bolt - plug is also installed in the inside of the body of the gas valve. The valve is actuated using special handles, which are either made together with a cone-shaped valve, or attached to it during the assembly of the gas valve.
Works like a crane as follows. When the through hole in the cone-shaped damper coincides with the holes in the gas valve body for the entrance and exit of natural gas, there is no obstacle to the passage of natural gas through the gas valve. In this case, the gas valve is open. If the through hole in the cone-shaped flap does not coincide with the holes in the housing for the entrance and exit of natural gas, then the gas valve is closed. And if the through hole partially does not coincide with the holes in the gas valve body for the entrance and exit of natural gas, then the valve is partially open, and natural gas will pass through it partially. The direction of the holes relative to each other is regulated by turning the cone-shaped flap in the cone-shaped socket.
To account for the use of natural gas by consumers, gas meters of four types are mainly used.
1. Membrane (diaphragm) gas meters. This type of gas meters are used to calculate the use of natural gas of small volume, not more than 12 cubic meters per hour. They are mainly used for counting natural gas of individuals in private sectors, as well as in enterprises and organizations where the use of natural gas is not an industrial necessity. The main advantage of membrane meters is the ease of manufacture, low cost, relatively accurate counting, even pre-use, of natural gas. The main disadvantage is that such meters practically do not transfer overloads, both temporary and permanent.
The counting mechanism in such meters is mounted on the outside of the gas meter and is a peripheral device. It is given from the measuring mechanism mainly with the help of the shaft. The shaft is the only technical device that works both inside and outside the gas meter. The seal between the shaft and the housing is made with special rubber-like glands.
Works membrane meter as follows. The valve mechanism is designed so that, before any position, one of the fur-like chambers must be filled with natural gas, while the other is emptied. Before this, the filled fur-shaped chamber under the pressure of natural gas expands, setting in motion the crank and the lever attached to it. Through the lever is provided in a special way spool valve mechanism. Also, through another lever, movement is transmitted to the connecting rod of the opposite fur-shaped chamber, causing it to shrink, which leads to the displacement of natural gas that was previously filled. When the expandable fur-shaped chamber is filled to the permissible limit, the slide valve mechanism switches. In this case, the fur-like chamber, which was filled, will begin to empty, and the one that was emptied will be filled. This process will be repeated until new portions of natural gas are supplied to the gas meter under pressure.
Counting in a membrane gas meter is as follows. All fur-shaped chambers in the gas meter have the same volume. The counting mechanism is set up, so that it calculates how many times natural gas has come out of each chamber for a certain unit of time. The counting mechanism translates such calculations into a clear digital equivalent, and it is displayed on a special panel on the counting mechanism.
2. Rotary gas meter. This type of meter is one of the first to be used to calculate the consumption of natural gas by gas consumption devices. The main advantages of rotary gas meters are relatively high transmittance, relatively small size and weight, “tolerance” for overload, and similar meters are quite durable. The disadvantage of such meters is that their manufacture requires particularly careful adjustment of all parts. Relatively expensive materials are also used. All this leads to a comparatively high cost of rotational counters.
Rotary meters are mainly used in enterprises and organizations where the consumption of natural gas does not exceed 200 cubic meters per hour (boilers, bakeries, etc.). Sometimes they are used in the private sector for individuals.
A rotary gas meter consists of a body in which two eight-shaft are installed on a shaft in a special cavity. The shafts of pre-work are synchronized with the help of gear transmission. A counting drive shaft is connected to one of the eight-sized ox. The counting mechanism, as in the membrane counter, is a peripheral device. Therefore, the shaft drive works, as in the inside of the gas meter, and from the outside. The seal between the shaft and the housing is made with special rubber-like glands.
Works rotary counter as follows. The shafts in the cavity of the gas meter housing form the pre-work pockets. Before this, one of the pockets is necessarily located above the natural gas inlet in the gas meter housing. Pre-flow of natural gas into the pocket creates a certain pressure, which turns the eight-shaft. The eight-shaped shaft, with a pocket, turning to the output of natural gas, in the gas meter housing, releases natural gas. Natural gas from the pocket goes into the gas meter outlet. Meanwhile, over the inlet of natural gas, a gas meter, a new pocket is formed, which is also filled with natural gas to form pressure, which turns an eight-shaped shaft. For a complete revolution of all two eight-shaft rolls, four pockets are formed, which have the same volume of filling with natural gas.
The counting mechanism calculates how many full turns made over a certain period of time. Turns are multiplied four times, and multiplied by the volume of one pocket. The readings are converted to a digital equivalent and displayed on a special panel on the counting mechanism.
3. Turbine gas meter. Such meters are used in mainly enterprises and organizations where the consumption of natural gas is very high. Also, such meters operate on high-pressure pipelines. Such pressure of natural gas in the pipeline in the private sectors do not apply.
Turbine gas meters are very complex in design. The main details of such gas meters is the housing, inside which a turbine wheel is mounted on bearings.
Works turbine counter as follows. Passing natural gas rotates the turbine. From the turbine, the rotation is transmitted to the ferrite magnet drive shaft. Rotating, the ferrite magnet for one revolution turns on once a special switch (reed switch). An electric current is passed through the reed switch. Pre activation of the reed switch an electrical impulse is formed, which is fed to an electronic counting mechanism.
The counting mechanism on modern turbine meters is a mini computer system. Such a system not only counts the pulses and translates their digital equivalent, but also monitors the correct operation of the gas meter, and also signals an unauthorized intervention in the operation of the unit. The most up-to-date counting mechanisms of turbine gas meters are equipped with modems, through which all readings are transmitted directly to the gas servers to the inspection services.
4. Vortex flow meter. Almost the most complex device of the mechanisms of metering natural gas. Describing a vortex flow meter device does not make sense, since it is practically used in very large enterprises and organizations with a huge amount of natural gas consumption. They work on the basis of the dependence on the flow rate of the pressure oscillations that occur in the flow in the process of vortex formation or oscillation of the jet, or after an obstacle of a certain shape, installed in the pipeline, or a special twisting of the flow.
Counting mechanisms in such devices as well as on turbine meters are mini computer systems, some of which are equipped with modems.
There are also liquid gas meters. One of the most accurate gas meters. But because of the complexity of the design, and the complexity of their maintenance, such meters will mostly be exchanged in lab conditions. They work on the principle of the rate of ejection of certain gas substances, in certain portions, from a certain liquid substance (mainly from distilled water). The portions of ejection of the gaseous substance from the liquid are set by a lapata-shaped shaft of a special shape.