Information Zone Flow Meters – What Are They & What Do They Do? Share This Article: Copy to clipboard Copied A flow meter is a device used to measure the flow rate or volume of a liquid or gas moving through a pipe. They may be referred to by different names such as flow gauge, flow indicator, liquid meter & more, but the function - to measure flow - is essentially the same. What Are Flow Meters Used For? Two everyday uses are in the measurement of water & fuel. Households fitted with water meters are using flow meters to measure the volume of water entering the property & thus how much water is consumed. Similarly, when you fill your car with fuel, a flow meter measures how much fuel is being drawn & records it via a display on the pump. In commercial applications, flow meters will measure a variety of liquids of varying types & viscosity. The type of liquid being measured will play a major part in the type of meter being used. How Do Flow Meters Work? A Flow Meter will measure the volume or velocity of liquid passing through a measuring device. In the case of positive displacement (PD) meters, they measure the exact volume of liquid & are therefore highly accurate. Other metering technologies give a more general or “inferential” measurement by equating flow rate to volume. Are Positive Displacement Meters The Best Type Then? Although considered one of the most accurate metering technologies, establishing precise needs is important as there are pros & cons to using PD meters. One of the biggest advantages is accuracy. Many positive displacement meters are used in custody transfer applications in which weights & measures or measuring instruments directive (MID) approval is required. To achieve this high degree of accuracy, internal components are machined to extremely tight tolerances. With this in mind, PD meters have very small clearances & are therefore generally not suitable for use with abrasive liquids, slurries or liquids contacting particulate matter as these will damage the meter preventing it from recording correctly. PD meters are widely used, but not restricted to applications in which the volumes recorded directly influence how much people are charged. As previously mentioned, an example of this would be the measurement of fuel sold through a dispenser on a garage forecourt. How Accurate Does My Meter Need To Be? Not all applications require a high degree of accuracy. For example, highly accurate measurement of irrigation flows is generally not as critical as the accurate measurement of fuel delivery or domestic water. In applications such as irrigation, tolerances of 5-10% may be acceptable. In these cases a PD meter may not be the best choice of meter given that it is inherently a very accurate device. What Type Of Flow Meter Should I Use? A set of questions should be asked so as to establish the best type of meter to use for a given application: What liquid is being measured? What are the minimum & maximum flow rates? What are the accuracy requirements? What will the fluid temperature be (or range of temperatures)? What is the viscosity? What is the pressure? Will it be used in hazardous area? Is flow continuous or intermittent? How compatible is the liquid with materials of construction. A clear understanding of the service conditions & expectations of the instrument will help arrive at the best type of meter for the application.
