Comparison BMeters GSD8 1/2 HW 2.5 110 vs Novator LK-15G

Features of the design of a mechanical water metre (see "Principle of operation").

— Turbine. Metres in which water during operation passes through a turbine — a wheel with blades, the axis of rotation of which is parallel to the direction of flow. This mechanism is somewhat more expensive than the impeller (see below), but it allows you to effectively cope with the intense flow of water while providing good accuracy. Therefore, in mechanical metres with a nominal diameter (see "Diameter (DN)") of more than 50 mm, only turbines are installed; in 50 mm models, turbines are found along with impellers, and in devices of a smaller diameter they are not used at all. Also, note that all models with this type of metre are industrial (see "Type").

— Impeller. Water metres in which water during operation passes through an impeller — a wheel with blades, the axis of rotation of which is directed perpendicular to the flow of water. This design is simpler and cheaper than the turbine design (see above), but it has lower accuracy and is not well suited for large volumes of water. Therefore, only models with a nominal diameter (see "Diameter (DN)") of 50 mm or less are equipped with impellers; these are, in particular, all household appliances (see "Type") with a mechanical principle of operation, as well as some industrial metres of low productivity.

— Single jet. Metres in which water enters the measuring mechanism in a continuous stream, without divid...ing into separate jets. Compared to the multi-jet devices described below, such devices are much simpler, cheaper and more compact, but they are more prone to errors associated with uneven flow. This is not a serious drawback for domestic use but is unacceptable for accurate calculations. Therefore, only household metres are made single-jet (see "Type").

— Multi-jet. In metres with this feature, the water flow entering the impeller or turbine (see above) is pre-cut into several jets. Due to this, the most uniform effect on the measuring mechanism is ensured and the turbulence that occurs in the pipeline is compensated, which significantly increases the accuracy of measurements. The main disadvantages of multi-jet devices are the complexity of the design and higher price than that of single-jet ones. Thus, it makes no sense to use such metres for household measurements; but in the industrial sector (see "Type"), where accuracy is key, they are extremely common.

— Dry. Dry-running metres are called metres in which the counting mechanism is completely isolated from the water flowing through the device. Unlike wet-running devices, where this mechanism is in contact with water, in dry-running models, most of the hardware is separated from the water-measuring section by a sealed partition, and rotation is transmitted through a special magnetic coupling. This arrangement complicates and increases the cost of the design; on the other hand, metres are more reliable, resistant to dirt and durable than wet metres. In addition, they can provide some special features — for example, disconnecting the measuring mechanism without removing the entire device.

— Combined. Combined models are actually two metres in one case, connected in parallel. One of these metres is designed for small volumes of water, the second for intensive consumption; switching between them is carried out automatically — by a special valve that reacts to the flow rate. This design is not cheap, but it allows you to significantly expand the effective range of measurements and achieve high accuracy at both low and high flow rates. It makes sense to use combined models where the intensity of water consumption can vary over a very wide range, which cannot be covered by a conventional metre.

The maximum water pressure that the water metre is designed for — that is, the highest pressure under which it can work correctly indefinitely. Traditionally reported in megapascals; 1 MPa corresponds approximately to 10 bar (10 atm).

The water pressure in the pipe to which the water metre is connected must not exceed the permissible maximum — otherwise, the device may be damaged and even depressurized with a flood. At the same time, when buying a device for domestic water supply, this indicator can be completely ignored. The fact is that even the simplest household metres have an allowable pressure of 1 MPa (10 bar), and in the most reliable models it can reach 1.6 MPa (16 bar); at the same time, the standard pressure in the water supply system is 4-6 bar, and it rises to 10 bar only occasionally, during tests of hydraulic systems. So you need to pay attention to the maximum pressure only in cases where the water metre is selected for a non-standard water supply system, where the pressure can exceed 1 MPa — an autonomous circuit with self-selected pumps, a production line, etc. Detailed information on choosing for such cases can be found in special sources.

Minimum water flow for this metre model.

The minimum flow rate is the smallest flow rate at which the counting mechanism can provide measurement with an acceptable error of ±5%. This deviation is higher than the counter error in the standard mode (from Qt to Qn, see below for details), it is considered undesirable, but generally acceptable. But when the flow rate drops below Qmin, the error increases to unacceptable values, and there is no question of acceptable measurement accuracy. So, ideally, it is worth choosing a metre in such a way that its Qmin is not higher than the water consumption at the minimum intensity of consumption. Detailed recommendations for estimating the actual water consumption for different water supply systems can be found in special sources.

Transitional water consumption for water metre model.

The transitional flow rate is the flow rate at which the maximum measurement error changes — namely, decreases: in the range from Qmin (see above) to Qt it is ±5%, and at the Qt level and above it drops to ±2%. In other words, Qt is the smallest flow rate at which the device gives not just an acceptable, but a minimum error. Thus, the optimal consumption intensity for any metre is in the range between Qt and Qn (see below), and it is this range that is best to focus on when choosing.

Detailed methods and recommendations for estimating water consumption for a particular water supply system can be found in special sources.

Nominal flow rate for this metre model.

It is the highest flow rate at which the device can work indefinitely (during the entire service life) without failures, malfunctions and exceeding the maximum allowable error (± 2%). For a short time, a higher flow rate is also allowed (for more details, see “Maximum water flow (Qmax)”), however, the regular mode is still the mode in which this rate does not exceed Qn. So this parameter is the main one when choosing a device. Ideally, the actual water flow should always be in the range between the nominal and transitional (see above) flow.

Maximum water flow for water metre .

The maximum flow rate is considered to be the highest flow rate at which the device can operate for a short time (less than 1 hour per day and less than 200 hours per year) without failures, malfunctions and exceeding the maximum allowable error (± 2%). For several reasons, this figure is usually twice the nominal flow rate Qn (see above). When choosing a metre for maximum flow, you need to take into account the peak consumption of the system that it serves — that is, the flow rate when all consumers are turned on maximum at the same time: this rate should not exceed Qmax, otherwise the metre will not be able to cope with its task normally. If the system is constantly operated in the maximum consumption mode, then it is worth choosing not by Qmax, but by Qn.

Sensitivity threshold for this water metre model.

The sensitivity threshold is the lowest flow rate at which the device begins to respond to the movement of water and record the flow; at a lower speed, the measuring mechanism simply does not distinguish between flow and still water. The lower this indicator, the less likely it is that, at low consumption, water will be consumed without accounting. In household models (see "Type") the sensitivity threshold does not exceed 40 L/h, there are also much lower figures — 10 L/h, or even 5 L/h. In industrial metres designed for large industries, there are values of hundreds of litres per hour.

Pressure loss in the water supply system occurs at maximum water flow due to the hydraulic resistance of the water metre; in other words, the difference between the pressure in front of the counter and immediately after it at a flow rate of Qmax.

This parameter is relevant primarily for mechanical models (see "Principle of operation") — in other varieties, the flow resistance is so insignificant that the pressure drop can be neglected. The flow rate Qmax is detailed above; here we note that it is at this level that the resistance reaches its highest values, and it is by Qmax that it makes sense to evaluate possible pressure losses. These data are used in some hydrodynamic calculations — in particular, to assess whether there is enough pressure at the points of water intake at maximum consumption. However, pressure losses in modern metres are small, usually, they do not exceed 0.1 MPa (1 bar).

The size of the threaded connection provided in the metre with the corresponding type of installation (see "Connection type").

Ideally, the metre itself, other components of the metering system (such as a filter and a check valve) and water pipes should have the same threaded connection diameter — this eliminates fuss with adapters and problems associated with speed drops due to uneven internal diameters. However, in some cases, you can use adapters. These situations are described in more detail in special sources.

Traditionally, water pipe thread sizes are indicated in inches and fractions of an inch. In modern water metres, the following sizes are mainly found: 1/2 ", 3/4", 1", 1 1/4", 1 1/2", 2", 2 1/2". In this case, the thread diameter is associated with diameter DN (see above): larger DN requires larger fasteners. However, there is no rigid dependence here — for example, a metre with DN 20 can be equipped with both 3/4 "and 1" threads.