"Zhuanzhuan" Smart Lecture: Assessment of Causes and Solutions for Self-rotation of Domestic Water Meters
The self-rotation of vane wheel water meters is a common challenge faced by the global water supply industry. Water meter self-rotation refers to the phenomenon where the meter accumulates readings even when no water is being actively used, due to the reciprocating flow of water within the pipelines, provided that minor leaks from household water fixtures (such as flushing toilets, taps, etc.) have been ruled out.
The cause of water meter self-rotation is the potential presence of unsteady flow within the water supply pipes, which refers to water flow with constantly changing direction, velocity, and pressure. This type of flow is a transient flow that can generate minor water hammer effects. Some transient flows repeat at fixed intervals, forming pulsating flow. The water flows that cause self-rotation in vane wheel water meters are precisely these transient or pulsating flows. The internal metering mechanism of vane wheel water meters is susceptible to interference from such flows because during forward inflow, water enters from the bottom and exits from the top, driving the gears to rotate forward, whereas during reverse inflow, water enters from the top and exits from the bottom, driving the gears to rotate in reverse. The resistance encountered during these two-phase inflows is different. Although the inflow volume from both directions might be equal, the net movement of the pointer is not, often resulting in more forward movement than reverse, which can accumulate a certain reading over time. The self-rotation phenomenon is more likely to occur in high-rise buildings and where multiple user meters are installed closely together.
Methods and Evaluation for Solving Water Meter Self-rotation:
Eliminate the Source of Pulsation: This includes maintaining stable water pressure upstream of the meter, reducing severe pressure fluctuations and water source turbulence caused by facilities like pumps, ensuring components that may cause flow disturbance are installed as far away from the meter as possible, properly installing pipeline air release valves, and inspecting and addressing pipe sections prone to forming air pockets. However, due to variations in building locations and water usage patterns, the inherent introduction of air during the water production process, pressure fluctuations in the supply network, and the presence of air pockets in some pipes are currently unavoidable phenomena. Additionally, less-than-ideal pipeline layouts and mutual interference between multiple user meters connected in parallel also contribute to pressure pulsations, making it difficult to eliminate them entirely. The approach is often limited to localized modifications when problems are identified.
Install Check Valves with Damping Springs: This method uses damping to reduce pulsation pressure and amplitude, stabilizing the flow. However, it leads to increased pressure loss and is not suitable for widespread use. The cost of installing a good quality steel check valve is estimated to increase the cost by over 50% compared to the water meter price itself. Therefore, installing check valves has both advantages and disadvantages. While they can prevent self-rotation caused by unstable water pressure or air pockets, the drawbacks include increased flow resistance affecting end-use, potential issues with poor quality or insufficient sensitivity in some valves, added complexity and maintenance difficulty for the pipeline system, and potential impacts on normal meter operation and user convenience. Thus, installing a check valve is an option, but not necessarily the optimal solution for protecting meters from pressure pulsations.
Replace with Other Types of Water Meters:
(1) Replace the meter with a vane wheel water meter having slightly lower sensitivity, making it less affected by minor pulsations. However, this reduces the overall metering performance of the meter.
(2) Replace the meter with a volumetric (piston) water meter, whose metering performance is unaffected by pulsations. But its piston structure requires higher water quality; otherwise, it is prone to jamming, disrupting normal water use. Therefore, suitability depends on whether the pipeline water quality meets potable standards.
(3) Replace the meter with an electronic water meter capable of bidirectional measurement. However, domestic water meter manufacturers in China have not yet ventured into developing these for the residential market, and they come with higher costs.
Any solution must consider the cost of implementation, general applicability, feasibility, and reliability.
Water meter manufacturers produce products according to the national standard GB/T 778-2018 "Water meters for cold potable water and hot water." Prototypes must obtain national type approval, and each meter must undergo mandatory metrological verification according to the national metrological verification regulation JJG 162-2019 "Water meters for cold potable water" before installation and use. Installation is permitted only after passing checks for appearance, function, sealing, and indication error. Manufacturers provide installation instructions with the product to guide correct installation and use.
Valves, check valves (if installed), etc., used in the pipeline before and after the water meter belong to other plumbing fittings. Generally, water meter manufacturers do not produce these; they are selected, used, and quality-controlled by the water utility department.
The choice of vane wheel water meters as the primary domestic metering devices by water utilities in China is based on the water quality and network conditions in most towns and cities. These meters offer relatively good tolerance to water quality (small particle impurities can pass through without affecting operation), have a suitable flow range ratio, and are cost-effective. However, they have relatively high pressure loss (typically the highest level, Δp63, in the standard series for meter pressure loss) and higher installation requirements (requiring certain lengths of upstream and downstream straight pipe). With improvements in local water quality in some areas or the use of localized water purification devices in some residential complexes, the use of volumetric (piston) water meters is increasing. These have lower installation requirements, their metering performance is insensitive to water supply pressure fluctuations, but they come at a higher cost.
Therefore, there is no subjective intention by water utilities or water meter manufacturers to install measures like check valves to eliminate pulsating flow as a means of "legitimately infringing" upon residential consumers.
The occasional self-rotation of residential vane wheel water meters due to pressure pulsation, while not widespread and involving minimal water volume, generates negative feedback and is an issue that deserves attention. The water meter industry and the water supply industry are continuously exploring solutions. Although several methods exist, a standardized solution has not yet been established. Currently, for existing cases, measures like modifying pipelines, replacing with other meter types, or optionally installing check valves can be taken. For properties that will be unoccupied for extended periods, it is recommended that residents shut off the main water supply valve to avoid accidental leaks and metering disputes.
