There are a few different types of water meters. They differ in the method used to measure water volume, and the flow control and measurement devices in the water meter itself. Learn more about the three most common types of water meters below.
Type 1 - Displacement Water Meters
Displacement water meters measure how much water occupies a given space. The water flow displaces the measuring device according to the volume of water in either gallons or cubic feet that passes through the meter. A piston or a mutating disk controls the movement of a magnet that activates the water volume register.
Type 2 - Positive Displacement Meters
Positive displacement meters or PD meters are the most common water meters for homes and small businesses. They can measure small volumes of water at low flow rates to a high degree of accuracy. The water pipes in displacement water meters range from as small as 5/8 inch up to 2 inches in diameter. A displacement meter is made of brass, high-impact plastic, and stainless steel. The measurement register consists of a clear plastic bubble over the odometer-type or LCD display gauge. For measurements of less than 1/10 of a gallon, a sweep hand is also used on the measurement register. These meters can also be installed in separate units of a condominium or apartment to track individual water usage.
Type 3 - Velocity Meters
The speed at which the water moves is measured by velocity water meters. The velocity through the meter's specific volume is measured and converted to units of volume, either gallons or cubic feet. These meters can be calibrated to adjust the accuracy of the measurement. There are a few types of velocity-based water meters.
1. Single and Multiple-Jet Water Meters
Single and multiple-jet water meters use velocity to measure water volume. The water flow turns an impeller which rotates at a known speed compared to the water speed. These meters have internal strainer grids to prevent the jets from clogging with particles in the water. They are used for low-volume applications as the impellers cannot withstand high flow rates.
2. Turbine Water Meters
Turbine meters are used for water pipe diameters up to 12 inches across. They are used for high-volume commercial sites such as factories and large office complexes, and as control meters for sections of a town or city. Fire hydrant water meters are turbine water meters.
3. Compound Water Meters
In circumstances where water flow can vary from high velocity to low velocity, a compound meter can accurately measure water usage. These have two measuring components and a valve to control the flow rate to each. The turbine meter handles high flow rates and a multi-jet meter gauges the lowest flow. The utility reader adds the totals indicated on both meters to determine total water usage.
4. Electromagnetic and Ultrasonic Meters
A pair of electromagnets can measure water flow in or out of the system in a "mag meter" based on fluid induction principles. Ultrasonic meters send sound waves through water to measure its speed, and derive a water volume reading. These are used in large-volume applications and for fluids other than water.