Mechanical
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.
Sensitivity threshold, less than
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.
Threaded connection size
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.
Dimensions
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.
Length with fittings
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.
Country of origin
The country specified as the manufacturer of the water metre.
In evaluating this information, it is worth considering two points. On the one hand, the “homeland” of the brand under which the water metre is produced is usually indicated as the country of manufacture; the actual place of production may be located in another state. On the other hand, the quality of goods is determined not by the place of their production or the homeland of the brand, but, first of all, by how carefully this quality is controlled by a particular company. So you should pay attention to the country of origin mainly when you fundamentally want (or do not want) to support a company from a certain country. It is better to evaluate the overall quality of the water metre by the overall reputation of the brand and by the price category of a particular model.
