Water temperature
The purpose is indicated by the temperature of the water with which the metre can be used.
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For cold water. Metres intended for use in cold water supply systems and not designed for hot water. They are blue in colour as standard. In most of these models, the maximum water temperature (Tmax) is from 30 to 40 °C — this is quite enough for traditional water supply systems. However, there are also higher rates — up to 50 °C inclusive. Such metres will be useful where the cold pipeline may be subjected to additional heating and quite warm water may flow through it. An example is a stand-alone water supply system, some of the pipes of which are exposed to direct sunlight and can become very hot.
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For hot water. Metres intended for use in hot water supply systems; traditionally painted red. The standard temperature in DHW systems with centralized water supply is 65 °C, but higher values are possible. Therefore, in such metres, the maximum water temperature (Tmax) is not lower than 90 °C, and in the most advanced models — 95 °C. Note that such devices can easily cope with cold water, so technically it is quite possible to put a hot water metre in the cold water system; however, this is not justified in fact, since constant operation in abnormal mode adversely affects accuracy. And for water supply with a very unstable temperature, it is better to use universal metres (see below).
...— For cold/hot water. Metres that are equally well suited for both hot and cold water. Like specialized models for hot water supply, they have a maximum allowable temperature of at least 90 °C; the main difference is that this variety provides almost the same accuracy at any water temperature. Such properties are useful, first of all, if the temperature in the water supply is not constant, especially if the "hot" and "cold" periods take approximately the same time intervals. However, nothing prevents the use of such metres even at a stable temperature — except that the cost of universal models will be somewhat more expensive than specialized devices of similar quality.Minimum water flow (Qmin)
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.
Max. water temperature (Tmax)
The highest water temperature allowed for water metre.
This parameter is directly related to the purpose (see above): in devices only for cold water, Tmax is usually in the range of 30...40 °C heating water in a pipeline exposed to the sun). For metres that can be used with hot water, this figure is 90...95 °C.
Of course, in no case should the maximum water temperature be exceeded — this can lead to damage to the metre and even an accident with a flood” Putting a metre with Tmax at a level of 90 °C and above in a cold water supply system makes sense only if the device was originally designed for both hot and cold water; see "Suitable for" for details.
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.
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.
