WATER METERING: - water metering is the process of measuring the water use. Water meter is a device which measures the volume of water flowing through a pipe line system. Generally water meters are provided to measure the volume of water used by residential and commercial buildings that are supplied with water by a public water supply system. Water meters are also used at a water source to determine flow through a particular portion of the system. Normally, water meters measure flow in cubic meters (m3), some electronic meter can also display rate-of-flow in addition to total usage.
Water meters can be classified according to the technology used for their functioning. The choice depends on the flow measurement method, the type of end use, the range of flow rates and accuracy requirements in measurements.
Type of water meter: - water meters can either be mechanically driven or sensor based with each having specific attributes to suit various operating conditions. There are different types of water meters.
1. Mechanical water meters
2. Electromagnetic flow meter.
3. Ultrasonic flow meter etc.
Based on the measuring mechanism, meters are generally classified as
Ø Volumetric type : - volumetric type is not produced or used for water supply applications in india.
Ø Velocity type :- which are also called as inferential type meters are further classified as,
· Single-jet : - in single-jet water meters water jet impinges at a single place on the periphery of the rotor.
· Multi-jet :- in multi-jet meters, water impinges at several points simultaneously .
In india, water meters classified as,
· Turbine type :- these types meters consist of a turbine rotor rotating about the axis perpendicular to the flow and up to 50mm sizes of water meter are called domestic type.
· Bulk type or wolman meter :- woltmann type meters consist of helical blade rotating about the axis of flow and above 50mm sizes of water meter are called bulk type or wolman meter .
However, many water utilities have selected multi jet meters and achieved satisfactory performance in india.
Generally, water meters are classified based on the flow rates of operation.
Indian standards mention class a and b only. Class o specified earlier in indian standard has been removed in august 1999. Class c and class d meters are also mentioned in international standard. However, they are not used in india.
· Class A: - These Are Non magnetic type mechanical mechanism water meter. It can install only horizontally.
· Class B: - These are magnetic type mechanical mechanism water meter. It can install horizontally as well vertically.
Ø Mechanical water meter:-
Mechanical meters are positive displacement flow meters. They operate by isolating and counting known volumes of a fluid, while feeding it through the meter. By counting the number of passed isolated volumes, a flow measurement is obtained. These meters are suited for measurement of clear water with little turbidity and generally less expensive than non-mechanical types. Hence these are commonly used in urban water supply systems. However, they have a higher maintenance requirement.
Ø Working principle:
An impellor is rotated by water passing through the meter. The rotation of impeller is then translated into a volumetric reading. The mechanism is calibrated by an adjustable device that is preset and security sealed. These meters are available in various sizes and require full water flow in the pipeline during measurement.
Ø Advantages of mechanical meter:
· These are reliable and provide reasonably accurate means of measurement provided meter is correctly installed.
· The initial cost is relatively low.
· The in-line maintenance is simple.
Ø Disadvantages of mechanical meter:
· Mechanical parts can be damaged, making frequent accuracy testing necessary.
· Prone to wear in silty water, resulting in loss of accuracy and frequent need for replacement.
· Some head loss possible.
· Short service life.
Ø General features of mechanical water meter :
· The meter should be leak proof and totally sealed in metallic outer body.
· It should be repairable without interrupting water supply.
· It should have removable mechanism which ensures easy maintenance.
· Impeller should be protected by strainer cover.
Reliable sensitive metrology and low pressure loss.