The single jet water meter is a mechanical volumetric measurement instrument widely used in residential buildings and small commercial premises. Its core design concept is to utilize the principles of fluid dynamics to convert the kinetic energy of the flowing water into mechanical energy for measurement. The working principle can be broken down into the following key steps:
1. Flow diversion and jet formation
After water enters the water meter housing from the inlet pipe, it does not directly impact the impeller. First, the water passes through a carefully designed diversion chamber or smoothener. This structure is crucial as it is responsible for sorting and stabilizing the incoming water flow, eliminating possible turbulence and vortices caused by pipe bends or valve opening and closing, ensuring the water flow is as smooth and uniform as possible. Subsequently, the adjusted water flow is gathered and directed towards a fixed single-hole nozzle, thereby forming a concentrated, high-speed, and directionally stable water jet.
2. Core drive: Impeller system
This directed jet precisely impacts the blades of the impeller (rotor). The impeller is typically made of lightweight, corrosion-resistant engineering plastics (such as polyoxymethylene), and its axis is mounted on a very hard gemstone bearing or ceramic bearing to minimize frictional resistance. The force exerted by the water jet on the curved surface of the blades generates a rotational torque, driving the impeller to start rotating. The rotational speed (n) of the impeller is in a linear proportional relationship with the instantaneous flow rate (Q) passing through the water meter within a certain range, that is, the greater the flow rate, the faster the jet speed, and the higher the rotational speed of the impeller. This is the fundamental physical relationship for the water meter to achieve measurement functionality.
3. Motion conversion and seal transmission
The rotational motion of the impeller needs to be transmitted to the upper counting mechanism, while ensuring that the measurement chamber and the reading chamber are completely hydrostatically isolated to prevent water from entering the display part. This critical task is accomplished by a magnetic coupling transmission system. Below the impeller main shaft, there is a permanent magnet, and on the other end of the transmission shaft of the counting mechanism, there is also a magnet. These two are formed into magnetic coupling through a non-magnetic isolation layer (usually a copper cover or plastic cover) on the shell. As the impeller rotates, it “non-contactingly” drives the magnet of the counting mechanism to rotate synchronously, achieving sealed transmission of motion, eliminating the risk of leakage.
4. Cumulative measurement and display
The counting mechanism receives the rotational motion and converts the high rotational speed of the impeller through a precise gear reduction system into low-speed rotation of the pointer or digital wheel. The transmission ratio of the gear system is calculated precisely to ensure that a specific number of rotations of the impeller exactly corresponds to one unit volume of water (such as 1 liter or 0.01 cubic meters). Finally, the cumulative water volume is clearly displayed on the pointer counter or pointer-type dial, making it easy to read directly.
Performance characteristics and application scope
The single jet water meter has a relatively simple structure and is cost-effective. Its measurement accuracy is best in the medium-flow range (typically the nominal flow range of Q2 to Q4). However, since the water only impacts the impeller from one direction, the starting torque is relatively large at very low flow rates, and the sensitivity is slightly inferior to multi-shot water meters; at extremely high flow rates, the load on the impeller shaft system increases, which may affect accuracy and lifespan. Therefore, it is most suitable for daily water usage metering scenarios where the water flow is relatively stable and has little fluctuation. Its reliable structure and the advantage of not requiring an external power source make it one of the mainstream choices for urban and rural water supply metering at the household level.