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 widely spread natural gas is propane and methane.
We have the same goal: to understand how systems and mechanisms work on the braking, stopping and twisting of household gas meters. Therefore, only the low-pressure natural gas transmission system will be considered (for brevity, we will refer to it as LNG).
To control the flow of natural gas through LNG, cork valves are mainly used. Such cranes are very reliable, because during operation, all parts are constantly rubbed together, ensuring a permanent reliable leakproofness of the device, in general.
There are similar cranes from the shell, inside which is made a special cone-shaped nest, as well as openings for the entry and exit of natural gas. A cone-shaped flap is installed in the conical socket. A special through hole is made in the shutter, through which natural gas will pass. The cone-shaped shutter is tightly pressed against the walls of the cone-shaped seat by means of a special spring. The spring pressure on the damper is adjusted by means of a special bolt-plug. Spring and bolt - plug is also installed in the interior of the gas cock. The flap is actuated by means of special handles that are either integrated with the cone-shaped flap or attached to it during the assembly of the gas cock.
A similar crane works as follows. When the through hole in the cone-shaped flap coincides with the holes in the body of the gas cock for the entry and exit of natural gas, there are no obstacles for the passage of natural gas through the gas cock. In this case, the gas cock is open. If the through hole in the cone-shaped flap does not coincide with the holes in the body for the entry and exit of natural gas, the gas cock is closed. And if the through hole partially does not coincide with the holes in the body of the gas tap for the entry and exit of natural gas, then the tap is partly open, and the natural gas through it will pass partially. The direction of the holes relative to each other is adjusted by turning the cone-shaped shutter in the cone-shaped seat.
To account for the use of natural gas consumers mainly use gas meters of four types.
1. Membrane (diaphragmatic) gas meters. Such a type of gas meters are used to calculate the use of natural gas of small volume, no more than 12 cubic meters per hour. They are used mainly for the calculation of 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 counters is simplicity in manufacturing, low cost, relatively accurate calculation, even the lowest use, of natural gas. The main drawback is that such meters practically do not tolerate overloads, both temporary and permanent.
The counting mechanism in such counters is fixed from the outside of the gas meter and is a peripheral device. It is derived from the measuring mechanism mainly by means of 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 body is made by means of special rubber-like seals.
The membrane counter operates as follows. The valve mechanism is arranged so that, before any of its positions, one of the bellows chambers should be filled with natural gas, and the other emptied. In this case, the filled mech chamber under the pressure of natural gas expands, bringing into motion the crank and lever attached to it. Through the lever is a special way spool valve mechanism. Also, through the other lever, movement is transmitted to the connecting rod of the opposite bellows chamber causing it to contract, which leads to the displacement of the natural gas that was previously filled. When the expandable bellows chamber is filled to the allowable limit, the spool valve mechanism will switch. In this case, the fur-like chamber that was filled will begin to empty out, and the one that is emptied will be filled. Such a process will be repeated as long as new portions of natural gas enter the gas meter under pressure.
Counting in the membrane gas meter is as follows. All the bellows in the gas meter have the same volume. The counting mechanism is set up, so that it calculates how many times natural gas has been emitted from each chamber for a certain time unit. Counting mechanism such a calculation translates into an understandable digital equivalent, and it is output to a special panel on the counting mechanism.
2. Rotary gas meter. This type of meter is one of the first that has been used to calculate the consumption of natural gas by gas consumption devices. The main advantage of rotary gas meters is relatively high transmittance, relatively small size and weight, "tolerance" to overload, and similar counters are quite durable. The disadvantage of such counters is that their manufacture requires a particularly careful adjustment of all the details. Also relatively expensive materials are used. All this leads to a comparatively high cost of rotary counters.
Rotary counters are mainly used in enterprises and organizations where natural gas consumption does not exceed 200 cubic meters per hour (boilers, bakeries, etc.). Sometimes they are used in private sectors for individual individuals.
The 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 in advance with the gear drive. To one of the eight-shaped oxen is connected the drive shaft of the counting mechanism. The counting mechanism, like a membrane counter, is a peripheral device. Therefore, the shaft drive works, as well as in the nutria of the gas meter, and with the outside. The seal between the shaft and the body is made by means of special rubber-like seals.
The rotary counter operates as follows. The shafts in the cavity of the body of the gas meter form before the work of the pocket. First of all, one of the pockets is located above the natural gas inlet in the body of the gas meter. Pre-arrival of natural gas in the pocket creates a certain pressure, which turns the eight-shafts. The eight-shaped shaft, with a pocket, turning to the exit of natural gas, in the body of the gas meter, produces natural gas. Natural gas from the pocket goes into the gas meter outlet. Meanwhile, above the entrance of natural gas, a gas meter, a new pocket is formed, which is also filled with natural gas, forming a pressure that turns the eight-shaped shaft. For the complete 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 have been made over a certain period of time. Turns are multiplied four times, and multiplied by the volume of one pocket. Indications are translated into a digital equivalent and output to a special panel on the counting mechanism.
3. Turbine gas meter. Such meters are used in the main enterprises and organizations, where natural gas consumption is very high. Also, such counters operate on high pressure lines. Such pressures of natural gas in the gas pipeline in private sectors do not apply.
Turbine gas meters by design are very complex. The main parts of such gas meters are the housing inside which the turbine wheel is mounted on the bearings.
The turbine meter operates as follows. Passing natural gas rotates the turbine. From the turbine, the rotation is transferred to the drive shaft of the ferrite magnet. Rotating, the ferrite magnet for one revolution includes a special switch (reed switch) once. An electric current is passed through the reed switch. Before turning on the reed switch, an electrical impulse is generated, which is fed to the electronic counting mechanism.
The counting mechanism on modern turbine counters 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 unauthorized intervention in the operation of the unit. The most modern counting mechanisms of turbine gas meters are equipped with modems, through which all indications to the gas servers are directly transmitted to the inspection services.
4. Vortex flowmeter. Almost the most complex device from the mechanisms of accounting for natural gas consumption. It is pointless to describe the design 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 consumption of the frequency of pressure oscillations arising in the flow in the process of vortex formation or oscillation of the jet either after an obstacle of a certain form established in the pipeline or a special twisting of the flow.
Counting mechanisms in similar devices as well as on turbine counters 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 because of the complexity of the design, and their complexity in servicing, such meters are mostly exchanged in labarator conditions. They work on the principle of the speed of expulsion of certain gas substances, in certain portions, from a certain liquid substance (mainly from distilled water). Portions of the expulsion of the gaseous substance from the liquid are given by a shovel-shaped shaft of a special shape.