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.
Transitional water flow (Qt)
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.
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.
Protective cover
The presence of a special
protective cover on the water metre scale. Usually, such a cover is closed, it is opened only to check the readings. Such a detail protects, first of all, the transparent plastic with which the scale is covered — from bumps, scratches and dirt; thanks to this, the plastic remains transparent for a long time, does not become foggy and does not interfere with reading data from the scale. However, the role of the cover is not limited to this, it often provides additional protection for the case as a whole; and in some models, sensors are mounted in the cover to transmit data from the metre, used in remote control systems. Note that all these functions can be provided both in industrial and household metres (see "Type").
Verification interval
The maximum period of time between verifications allowed for this metre model.
Verification is carried out by specialists of the water supply company. As the metre wears out, it can begin to give wrong readings, so the purpose of such events is to make sure that the device gives the correct readings. Verification is associated with certain inconveniences: often the metre has to be removed entirely and put on a temporary plug for this time; in addition, the procedure is usually paid for. Accordingly, the longer the verification interval, the less often you will have to deal with these inconveniences.
Note that water companies refuse to accept data from metres that are not verified on time. The specific terms of the contract regarding verification may be different, so they should be clarified immediately when installing the metre. In particular, it is imperative to find out who should keep track of the time between verifications — the consumer or the water supply company.
