What are the Differences Between Volumetric Meter and Velocity-Type Meter?

A water meter, which records the amount of tap water used by a family, is usually installed on the main pipe. However, different water meters have different calculation methods. How does a water meter calculate water consumption? Today, we will introduce two types of water meters and their differences.

Velocity-Type Meter

The Composition and Working Principle of Velocity-Type Meters

The velocity-type meter is mainly composed of hull, water filter, impeller disc, impeller and gear counter. During work, the water flow will pass through the water filter screen outside the impeller disc, which will sieve off foreign matter such as rust, grit, iron filings in the water, and then flow in through multiple slots in the lower part of the impeller disc. These slotted angles are in the position to let the water flow impinge on the blade from all directions to make the impeller rotate, which brings about the spiral rise of the water flow, and finally, the water is discharged from the water tank on the upper part of the impeller disc.

Calculation of Velocity-Type Meters

In normal operation, the volume of water flowing in a unit time is equal to the total area of the slot in the lower part of the impeller disk multiplied by the water flow speed. Due to the fixed total area of the slot, the flow is proportional to the speed of the water flow, and moreover, the faster the water flow, the faster the internal impeller turns. As a consequence, the impeller speed and flow are also proportional. The number of revolutions of the impeller corresponds to the volume of water flowing through the impeller, and at the same time, the impeller drives the pointer and character wheel with different digits through the gear set to record the water consumption. However, with different water flows, the velocity-type meters used to estimate water consumption from the water flow speed will have a relative error of 2% to 5%.

Volumetric Meter

The Composition and Working Principle of Volumetric Meters

The main structure of the volumetric meter includes two internal and external cavities, a water inlet, a water outlet, a baffle and a piston. The piston moves inwardly with the inner wall of the cavity under the action of water pressure. In the outer or inner ring, the water will flow from the water inlet and then be driven to the water outlet to be discharged, which is cyclic.

Calculation of Volumetric Meters

Although the cycle of water in and out of the inner and outer rings is slightly different, in general, the amount of water flowing through one revolution of the piston is equal to the total volume of the inner and outer ring cavities. Because of this fixed total volume, the number of piston revolutions recorded by the gear is the amount of water used.

Volumetric meters have the capability to calculate water consumption directly through volume without complex conversion, and furthermore, the relative error can be controlled below 2%.

Overall, the velocity-type meter has a simpler structure and is easier to manufacture, while a volumetric meter is more accurate. No matter which type of water meter we choose, it must be maintained regularly!