Water meters measure the volume of water used by residential and commercial building units that are supplied with water by a public water supply system. They are also used to determine flow through a particular portion of the system.We examine 4 common water metres used in Kenya.
1.Displacement water meters
Displacement water meters are common water metres used in Kenya. They rely on the water to physically displace the moving measuring element in direct proportion to the amount of water that passes through the meter. The piston or disk moves a magnet that drives the register. There are two main types of
displacement meters: nutating disc and oscillating piston.
Displacement water meters are suitable for low to medium water flow rates with diameters typically ranging from 13 to 50 mm. They tend to be more accurate than velocity meters at low flow rates.
Due to its inner structure, displacement meters are sensitive to turbid water. Hence, an external strainer needs to be installed upstream when metering water with considerable amount of suspended particles. The additional external strainer and the often in-built sieve/strainer have to be regularly cleaned. In case of high possibility for meter air flow, displacement meters have shown to be less sensitive.
A velocity meter measures the velocity of the flow through a meter of a known internal capacity. In order to determine the actual consumption, the speed of flow is
converted into flow volume. Two main types of velocity meters used in Kenya are: singlejet meter and multijet meters. Singlejet meters incorporate a single tangential jet. In a multijet meter, a tangential opening in the chamber directs the water flow across a multi-vaned rotor.
The output speed of the rotor is proportional to the quantity of water passing through the measuring chamber. The meter works mechanically much like a singlejet meter except that the flow at the rotor is directed equally from several points, not just one; this
minimizes uneven wear on the rotor and its shaft.
The singlejet meter is applicable for small flow rates (diameters typically range from 15 to 50.The multijet water meter is suitable for small and medium flow rates (diameters typically range from 15 to 150.When metering water with considerable amount of suspended particles velocity meters tend to be less prone to clogging compared to displacement meters.
This results in less additional effort for servicing. If the specific turbidity level is very high, an additional external strainer should be installed as well. Both, the external strainer and the often in-built sieve/strainer have to be cleaned regularly.
Ultrasonic Flow Meters (UFMs) use sound waves to determine the velocity of a fluid flowing in a pipe. Since no moving parts are incorporated, waste water and water with larger
concentrations of suspended particles can be metered accurately.
UFMs are mainly used for measurement of bulk flows (diameters typically range from 15 to 1,800 mm) and commonly used as ‘clamp-on’ meters to calibrate large diameter velocity meters. UFMs are typically supplied with a transducer that can be used in a range from 75 to 1,800 mm. By procuring a second transducer (smaller), the UFM can be used in a range of 15 to 75 mm.
An electromagnetic meter measures the flow rate of water by its electromagnetic properties instead of measuring it mechanically. They are also common water metres used in Kenya The installation configuration should be such, that the transmission main is filled with water at all times (e.g. through installed non return
Since no moving parts are incorporated, waste water and water even with high amount of suspended particles can be metered accurately. Electromagnetic water meters are more sensitive to low flows.Its usual diameter ranges from 2 to 1,800mm.