Being free of harmful chemicals, with a standard viscosity and usually fairly neutral pH, water is one of the easiest liquids to measure. Therefore, it can be handled by a huge range of different kind of meters. Water metering can be completed by turbine, variable area meters, electromagnetic, ultrasonic flow meters and more. The way you are using the water will impact which flow meter would work best for your metering solution. You need to consider water pressure, temperature, flow range, the purity of the water and more to work out which flow meter is best suited to you.
These flow meters have a simple mechanism, best described as a ‘float in a tube’. This mechanism is basic, meaning it’s one of the cheapest options, but it does result in a reduced accuracy. It makes it perfect when you want to track more approximate watering metering. With this flow meter, you have to take care to not exceed the working pressure or temperature, so it’s best for water that stays at standard levels. This is especially so with plastic tube units. Variable area flow meters are available for water flows as low as 1 cc/min up to 1000 l/min -- although accuracy is limited to 2-3 percent at best.
These devices are, again, perfect for water metering where high levels of accuracy are not vital and are, like variable flow meters, one of the cheapest options. They are available from ¼” up to 6” bore, allowing it to handle flow rates from a few litres per hour up to 600m3/hr. They are made from either brass or cast iron coated in epoxy. It works well whether you’re measuring cold or hot water. While mechanical water meters are usually offered with a mechanical non-reset totaliser, Flowquip can also supply them with a low-speed pulse transmitter so they can be used for remote totalising. The diameter of the flow meter specifies the type of connection: 2” and under feature BSP union process connections and those above have flanged. The maximum pressure rating of the mechanical water meters is 16 barg, with cold water rated 30-50ºC and hot water 90-130ºC.
Mechanical and variable area meters are the best options for low budgets and water metering that doesn’t need to be highly accurate. Which you choose will depend upon the flow rate of your water.
Turbine flowmeters are perfect when your water is working at a higher pressure - up to 30000 psig - and when you want to measure with a high level of accuracy. It’s also perfect for water than needs to be kept pure and hygienic as the turbine flow meter does not need to be fitted into the pipe. Turbines don’t have the same flexibility found in mechanical water meters and usually operate over a 10: turndown. However, they give much greater levels of accuracy: between 0.2 and 0.5%. Turbine meters can also be used in conjunction with other instrumentation. This has the benefit of providing an indication of flow rate and total as well as current and pulse output (according to your requirements).
Electromagnetic flow meters work perfectly when you need a water metering solution for water than contains suspended particles (such as solids) that would otherwise interrupt the functioning of flow meters with internal-pipe rotating mechanisms. With no internal moving parts, the flow in the pipe is uninterrupted, making it suitable for clean or dirty water, including the handling of slurries or other water with solid content. It is more expensive than turbine meters, but better suited for certain water measuring situations. It has the same high level as accuracy and the flow range at which is can operate is higher: 20:1 or better.
While ultrasonic flow meters are the most expensive water measuring solutions, they are also the most appropriate for situations in which the pipe can’t be broken into or the flow of water interrupted while a specialist fits your meter. It’s also great if measurements are required along multiple points in your process. While the initial outlay of one ultrasonic flow meter is more expensive, it’s cheaper than buying multiple meters to fit along different sections of your process. Ultrasonic flow meters work completely external to the pipe. They don’t come into contact with the water and have no moving parts. It means they are virtually maintenance free. While working pressure doesn’t affect the meter, it’s important not to exceed the temperate limit, which is usually around 130ºC, according to the specific variety of meter. It also provides a good level of accuracy although not as high as turbine flow meters: between 1-2%.
These are the key water measuring flow meters, although others can be used if the circumstances of your water flow require something different. These include coriolis, mass, vortex shedding and positive displacement meters. If you’re unsure about what meter would best suit your requirements, just get in touch with the experts at Flowquip.