Comparison BMeters GSD8 1/2 CW 1.5 110 vs Gross MTK-UA 15

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.

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.

The division value on the measuring scale of the water metre.

The division price is the minimum measurement step, the difference between two adjacent smallest units, in other words, the smallest difference in readings that the metre can display. The smaller this difference, the more detailed data the device produces. For example, a value of 0.01 m³ allows you to display data with an accuracy of the second decimal place — that is, such a metre will show, for example, a change in the amount of water consumed from 0.02 m³ to 0.03 m³, but will not perceive the difference between 0.022 m³ and 0.028 m³ (readings will remain at the level of 0.02 m³). However, modern water metres — even household ones — for the most part, have a lower division price, from 0.001 m³ and below.

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).

Installation method provided for by the design of the metre.

Modern metres can be designed for horizontal or vertical installation. The division, in this case, is carried out according to the location of the pipe into which the device is built; in the first case, the device is located with the scale up or to the side, in the second — only with the scale to the side.

The choice for this indicator depends primarily on the planned installation site of the metre. There is an opinion that a vertical installation contributes to greater accuracy, but it all depends on the specific model of the device. It is also worth noting that nowadays, horizontal placement is most popular; purely "vertical" models are rarely produced, and universal solutions that allow both installation methods are more common.

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.

General water metre dimensions in length, depth and height. Sometimes only one size can be indicated in this paragraph — the length: it is most important during installation, it is the length that is taken into account when choosing the required distance between the ends of the pipes. At the same time, it is worth remembering that between these ends, not only the metre itself is most often located, but also other devices and parts: connecting fittings, a valve, a coarse filter, a check valve, etc. Details on this can be found in special sources; here we note that for some models, the specifications separately indicate the length with complete mounting fittings (see below). Without fittings, the length can be from 80 – 100 mm in the most compact devices to 250 mm or more in the largest.

Depth and height, in turn, allow you to estimate how much free space around the pipe is needed for the normal placement of the metre.

The length of the water metre with complete mounting fittings installed on it.

The fittings are used when installing models with a threaded connection (see "Connection"). They are short pipes screwed onto the inlet and outlet of the metre and play the role of a kind of adapter between the device and other elements of the system (for example, a coarse filter and a check valve for a traditional household metre). Knowing the length with fittings installed, it is easier to calculate the required distance between the ends of the pipes: when calculating, you do not need to separately take into account the length of the fittings, they are already taken into account in this size.