The device and principle of operation of gas transmission systems.
The combustible gases that will be discussed, almost all are chemical compounds of hydrocarbons. The most common natural gases are propane and methane.
You and I have one goal: to understand how the systems and mechanisms for braking, stopping and twisting household-class gas meters work. Therefore, only a low-pressure natural gas transmission system will be considered (we will call it LNG for reduction).
To regulate the supply of natural gas through LNG, plug valves are mainly used. Such cranes are very reliable, since during operation, all parts are constantly rubbed together, providing constant reliable tightness of the device, in general.
Such taps consist of a body, inside which a special cone-shaped socket is made, as well as openings for the entry and exit of natural gas. A cone-shaped damper is installed in the conical socket. A special through hole has been made in the damper, through which natural gas will pass. The cone-shaped damper is pressed tightly against the walls of the conical socket using a special spring. The spring pressure on the shutter is regulated using a special bolt - plugs. Spring and bolt - plug is also installed in the nutria of the gas valve body. The damper is actuated using special handles, which are either made together with a cone-shaped damper or attached to it during the assembly of the gas valve.
A similar crane works as follows. When the through hole in the cone-shaped damper matches the holes in the body of the gas valve for entering and exiting 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 damper does not coincide with the holes in the housing for entering and exiting natural gas, the gas valve is closed. And if the through hole partially does not coincide with the holes in the body of the gas valve for entering and exiting natural gas, then the valve is partially open, and natural gas will partially pass through it. The direction of the holes relative to each other is regulated by turning the cone-shaped flapper in the conical socket.
To account for the use of natural gas by consumers, four types of gas meters are mainly used.
1. Membrane (diaphragm) gas meters. A similar type of gas meter is used to calculate the use of natural gas of small volume, not more than 12 cubic meters per hour. They are used mainly for calculating the 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 simplicity of manufacture, low cost, relatively accurate calculation, even with minimal use, of natural gas. The main disadvantage is that such counters practically do not tolerate 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 driven from the measuring mechanism mainly using a 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 using special rubber-like seals.
The membrane counter operates as follows. The valve mechanism is designed so that before any position one of the furry chambers should be filled with natural gas, and the other emptied. In addition, the filled furry chamber expands under the pressure of natural gas, causing the crank and lever attached to it to move. A spool valve mechanism is driven in a special way through a lever. Also, movement is transmitted through another lever, to the connecting rod of the opposite furry chamber, causing it to compress, which leads to the displacement of natural gas, which was previously filled. When the expandable furry chamber is filled to an acceptable limit, the spool valve mechanism will switch. In this case, the furry chamber that is filling up will begin to empty, and the one that is empty will fill up. A similar process will be repeated until new portions of natural gas enter the gas meter under pressure.
Counting in a membrane gas meter is as follows. All furry chambers in the gas meter have the same volume. The counting mechanism is set up so that it counts how many times natural gas has been released from each chamber in a given unit of time. The counting mechanism translates such calculations into an understandable 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 meters. The main advantage of rotary gas meters is their relatively high transmittance, relatively small size and weight, “tolerance” to overload, and similar meters are quite durable. The disadvantage of such counters is that their manufacture requires particularly careful fitting of all parts. Relatively expensive materials are also used. All this leads to the comparative high cost of rotary counters.
Rotary meters are mainly used at enterprises and organizations where the consumption of natural gas does not exceed 200 cubic meters per hour (boiler rooms, bakeries, etc.). They are sometimes used in private sectors for individuals.
A rotary gas meter consists of a housing in which two eight-shaped shafts are installed in a special cavity on the shafts. The shafts are synchronized using gears. A drive shaft of the counting mechanism is connected to one of the eight-shaped oxen. The counting mechanism, like that of a membrane counter, is a peripheral device. Therefore, the drive shaft works, as in the nutria of the gas meter, and from the outside. The seal between the shaft and the housing is made using special rubber-like seals.
The rotation counter works as follows. The shafts in the cavity of the body of the gas meter form pockets before operation. Before this, one of the pockets must be located above the natural gas inlet in the gas meter housing. As natural gas enters the pocket, a certain pressure is created which rotates the eight-shaped shafts. Eight-shaped shaft, with a pocket, turning to the exit of natural gas, in the body of the gas meter, releases natural gas. Natural gas from the pocket goes into the outlet of the gas meter. Meanwhile, a new pocket forms above the inlet of natural gas, the gas meter, which is also filled with natural gas to form pressure, which rotates the octagonal shaft. For a full revolution of all two eight-shaped shafts, four pockets are formed, which have the same volume of filling with natural gas.
The counting mechanism calculates how many full revolutions are made for a certain period of time. Turnover is multiplied four times, and is multiplied by the volume of one pocket. The readings are converted into 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 work on high-pressure lines. Such pressures of natural gas in the gas pipeline are not used in private sectors.
The turbine gas meters are very complex in design. The main details of such gas meters is a housing, inside of which a turbine wheel is mounted on bearings.
The turbine meter operates as follows. Passing natural gas rotates the turbine. From the turbine, rotation is transmitted to the ferrite magnet drive shaft. While rotating, a ferrite magnet turns on a special switch (reed switch) once. An electric current is passed through the reed switch. Before switching on the reed switch, an electrical impulse is generated, which is fed to the electronic counting mechanism.
The counting mechanism on modern turbine meters is a mini computer system. Such a system not only counts 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 modern 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 flowmeter. Almost the most complex device of the mechanisms for accounting for the consumption of natural gas. It makes no sense to describe the device of a vortex flowmeter, 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 fluctuations that occur in the stream during the process of vortex formation or stream oscillation, or after an obstacle of a certain shape installed in the pipeline, or special swirling of the stream.
Counting mechanisms in such devices as well as on turbine meters are a mini computer system, some of which are equipped with modems.
There are also liquid gas meters. One of the most accurate gas meters. But due to the complexity of the design, and the complexity of their maintenance, such counters will mostly be exchanged in laboratory conditions. They work on the principle of the rate of expulsion of certain gas substances, in certain portions, from a certain liquid substance (mainly from distilled water). The portions of the expulsion of the gas substance from the liquid are defined by a specially shaped lapate shaft.