How Mechanical Water Meters Work
The water meter on the water pipe has several small pointers arranged along a circular arc on the dial of the water meter. There is a small red triangle in the center. When the faucet is turned on and water is flowing, the small red triangle will rotate. As for the little hands, they hardly move at all whether the water is running or not.The words "m3" are also written on the dial, which means cubic meters. That is to say, the unit of reading of this meter is cubic meter. Because each cubic meter of water is exactly one ton, the reading is directly the ton, so the water fee can be easily calculated according to the reading (ton) of the total amount of water used.
So what is the working principle of the water meter?
In fact, it is very simple, because the shell of the water meter is fixed, its internal volume is fixed, and the water is flowing. It drives an impeller to rotate, and every time the impeller rotates, a constant volume of water flows through it. Therefore, as long as the number of rotations of the impeller is accumulated and multiplied by this constant volume, the total amount of water flowing through can be obtained.
We have already understood the principle, so let’s take a closer look at the inside of the water meter, because in order to prevent users from cheating, there is a lead seal on the cover, which is not allowed to be opened.
The internal structure of the water meter can be divided into three parts: the shell, the sleeve and the inner core from the outside to the inside. The shell is made of cast iron. After the water comes out of the water inlet, it passes through the lower annular space of the shell, which is called the "lower annular chamber". On the top of this annular space, there is an "upper annular chamber" which communicates with the water outlet. There is a filter screen with small holes at the bottom of the sleeve to filter out the sundries in the water. There are upper and lower rows of circular holes on the side of the sleeve. The holes are positioned exactly opposite to the upper and lower annular chambers of the casing. Obviously, the lower row is the water inlet hole and the upper row is the water outlet hole. Of particular note is that both rows of holes are drilled diagonally tangential to the circle, which works as shown in the animation. Note that the directions of the upper and lower rows of holes are opposite. Water flows in along the tangential direction from the lower drain hole, which is bound to form a rotating water flow, which is very important for the work of the water meter.
Let’s take a look at the inner core again. The inner core is divided into upper, middle and lower layers. What we see from the glass window is the upper layer, with only pointers and dials. In fact, the key is the lower layer. There is a plastic wheel inside, and there are many plastic blades on the edge of the wheel, as shown in the picture above (Figure 1), called "impeller".
The position of the impeller is just in the rotating flow formed by the lower hole of the casing, and the water flow impacts the blades around the wheel to generate torque and make the impeller rotate. The bigger the faucet is opened, the faster the water flow, and the faster the impeller turns.
The shaft of the impeller reaches the middle layer vertically upwards, and there is a small gear on the shaft, which is used to mesh with the "decimal number gear" to achieve the purpose of accumulating the number of revolutions. The function of the "decimal number gear" is that every time the one-digit gear turns ten times, the ten-digit gear turns one turn. In other words, the one-digit gear turns one revolution, and the ten-digit gear turns one-tenth of a revolution. The one-digit gear is the driver, which drives the ten-digit gear. In fact, two pairs of gears are used for each stage of decimal to make the direction of rotation consistent. One pair of transmission ratio is 9:30, and the other pair is 10:30. These two pairs are connected in series, and the total transmission ratio is this The product of two, which is 0.099999, can be approximated to 0.1.
According to this calculation, if you want to read seven digits (reading four digits before the decimal point is a black scale, and reading three digits after the decimal point is a red scale), you have to use 12 pairs of gears. In addition to some other uses, 18 shafts and 34 gears need to be squeezed into the small space in the middle layer, which can be regarded as a high-density installation. Unexpectedly, there are so many gears in a tap water meter!
Although we have entered the 21st century now, this kind of mechanical water meter will still serve us for a long time due to its simplicity and cheapness, its long-term use in humid environments without maintenance, and the fact that it does not need a power supply and does not affect its work during power outages. Although the water meter of electronic technology has appeared, it will take a long time to spread to our ordinary people's homes.