In order to clarify the working principle of the regulator more clearly, it is necessary to clarify the question: What conditions should the gas safe combustion have? For solid fuels to burn safely, there are two conditions: one is the right amount of combustion gas (air or oxygen), and the other is that the burning material maintains a certain temperature (usually above the point of ignition).
When solid combustion, the heat transfer mode of the burned part to the unburned part is conduction and radiation, and the combustion direction is developed from the outside to the center. When the solid burns, thermal expansion occurs, and the volume becomes large, but the change is small, and the displacement is almost zero. When the gas is burned, the heat transfer mode of the burned portion to the unburned portion increases the convection mode in addition to conduction and radiation, and the combustion direction is developed outward from the center. When the gas burns, it undergoes intense thermal expansion, and the volume of the product is hundreds of thousands of times before the combustion, and the displacement occurs at a relatively fast rate. Therefore, only satisfying the above two conditions is that the gas cannot be safely burned.
Modern combustion theory tells us that gas safety combustion must also have a third condition, that is, to maintain a certain difference in air pressure, so that the gas outflow speed is equal to the burning speed. Only in this way, when the dynamic balance is reached within a certain range, the flame can maintain a stable state, thereby achieving safe combustion of the gas. If the air pressure is too strong, the air outlet speed will be greater than the burning speed, causing the flame to burn away from the fire hole at a certain distance. This phenomenon is called the flame separation. If the gas pressure continues to rise, the flame will burn farther away from the fire hole, the stability of the flame 2 will be further destroyed, and the flame will be erratic until it is completely extinguished. This phenomenon is called fire. When the fire is off, the gas will continue to leak, forming a large amount of toxic or explosive gas in the air, which is easy to cause an accident; if the gas pressure is too small, the burning speed will be greater than the outlet speed, causing the flame to enter the fire hole and continue to burn. This phenomenon is called tempering. When tempering, incomplete combustion of anoxic state occurs, a large amount of toxic gas is generated, and the petroleum gas is also spilled outward, which is also liable to cause an accident.
Through a large number of experiments by engineers and technicians, it not only confirmed that the gas safety combustion should maintain a certain pressure difference, but also confirmed the gas of different components, the pressure difference required for safe combustion is not the same. For example: artificial gas, 80-100mm water column; liquefied petroleum gas, 250-350mm water column. The 2940Pa mentioned above is the average of these two values.
Let's go back to the regulator principle. When we open the angle valve on the cylinder (ie, the vent switch), the high-pressure liquefied petroleum gas passes through the inlet pipe and opens the valve gasket into the lower plenum. As the gas in the lower plenum increases, the pressure in the lower plenum increases. The rubber film is raised upwards. The volume of the upper air chamber gradually becomes smaller. When the upper air chamber pressure is stronger than the atmospheric pressure, the indoor air is slowly discharged from the breathing hole, and the pressure exciter is exhaled once. In this process, the right end of the lever moves up, and the left end is pressed down, so that the intake nozzle is gradually closed, and the air supply is stopped, so that the pressure of the lower air chamber no longer rises.
When the gas furnace switch is turned on, the gas pressure is reduced due to the outward output of the gas, the rubber film is concave, the right end of the lever is moved downward, the left end is moved upward, the valve pad is opened, and the high pressure petroleum gas enters the lower air chamber. In this process, the volume of the upper air chamber gradually becomes larger. When its pressure is lower than the external atmospheric pressure, the air enters the upper air chamber from the outer breathing hole, and the inhalation process of the pressure regulator is completed.
Therefore, during the burning process of the stove, the rubber film is continuously convex and concave, and the valve pad is driven by the lever, and is also opened and closed. In the whole dynamic change, we only need to guarantee the lever in the pressure regulator, the length of the left and right arms (note the characteristics of the left short and the right length), there is a reasonable proportion, plus the rubber film and the spring to the right end of the lever Applying a suitable amount of force will allow the valve mat to open much less than the closing time and have an appropriate ratio between the two periods. This proper ratio ensures the air pressure in the lower air chamber, which is always about 2940 Pa larger than the upper air chamber. For the upper air chamber pressure, it can be approximated as the external atmospheric pressure value at that time. This will make the pressure of the gas leaving the fire hole, always greater than the atmospheric pressure value of 2940Pa, and the gas will burn under steady state. This is the first subtlety in the design of the regulator.
The second subtlety, expressed in the design of the breathing hole, is so original. First, why is the breathing hole drilled on the edge of the upper bonnet? Instead of drilling in other locations that are easy to drill? Second, the diameter of the breathing hole is 0.8 millimeters. It can only pass through the smallest number of rust needles. Why is the aperture so small?
The hole is drilled on the rim of the bonnet to hold it against the rubber membrane. If the air pressure in the lower air chamber is too large, the rubber film will bulge upwards and immediately block the breathing hole, preventing the air in the upper air chamber from being discharged outward from the breathing hole. According to the law of Boyle's law, the air that is sealed in the upper air chamber has a certain amount of air, and its pressure is constantly increasing as the volume becomes smaller. That is pV=constant. The rubber film is prevented from being damaged due to the excessively large air pressure difference between the upper and lower air pressure, and the leakage of the petroleum gas due to the damage of the diaphragm is avoided.
The diameter of the breathing hole is 0.8 millimeters, but the depth of the hole is about 1 cm. The knowledge of fluid mechanics is fully applied here. When the fluid is in motion, there will be internal friction due to the retardation. The smaller the hole area, the greater the depth, the greater the internal friction and the greater the damping effect - the flow per second becomes smaller. In this way, the upper air chamber has a long time process during exhalation and inhalation, thereby ensuring that in the dynamic change, when the LPG is increased or depressurized, it is not a rapid increase, nor is it a rapid decrease, and the flame can be made. Stable combustion reflects the process of dynamic balance adjustment.
