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Flow meters are integral to the functioning of espresso machines as they measure the volume of water that enters the coffee group head or brew group. Flow meters are found at each group of most espresso machines and are there to ensure a consistent and accurate delivery of water quantity to the coffee grounds, a critical factor in maintaining the desired quality and consistency of every espresso shot.

Types of Flow Meters

Among the different types of flow meters, the paddlewheel, turbine, and vortex types are commonly known. However, in espresso machines, the paddlewheel type is the predominant choice. Typically equipped with either two or four magnets, the four-magnet variation is often found in high-end machines such as the Café Racer by Sanremo Coffee Machines, primarily for its enhanced precision. For those brewing single-origin coffees with longer extraction times, opting for an espresso machine incorporating a four-magnet flow meter can be advantageous.

Flow Meters Measure Water Volume

As water moves through the flow meter, the paddlewheel rotates, causing the magnets to pass by a field sensor that subsequently transmits an electrical signal to the espresso machine's control board, allowing for accurate monitoring and control.

It's important to note that flow meters serve as a tool to gauge water volume and do not need to be calibrated. Flow meters are rebuildable, but most equipment owners opt to just replace them when they begin to fail. Flow meters have little to no effect on flow rate. To ensure their optimal performance, it's crucial to maintain their integrity by using high-quality water, as the detrimental effects of mineral deposits or sensor malfunctions can significantly impact their functionality. Consulting your local service provider for advice on the most suitable water treatment options for your specific espresso machine can be beneficial in this regard.

The dosing volume of a machine can be set either by visual observation or by weight. In the absence of a display, the programming of the machine is set when the desired extraction is achieved. However, machines equipped with digital displays permit operators to configure the water volume by setting pulses or milliliters, although the ultimate assessment and setting of recipes is by evaluating the shot's quality, which still relies on a visual evaluation of the product. Only select high-end machines offer the option to set doses in milliliters, with some models like the Steam LP by Slayer Espresso, converting milliliters to weight through specific programming adjustments. Regular calibration for milliliters to weight conversion should occur, ideally on a daily basis, when changing coffee types, or following significant grind adjustments. This is essential for maintaining the accuracy of the machine's dosing settings.

Even in the case of advanced espresso machines like those from Victoria Arduino that incorporate the gravimetric system or others who utilize scales, the use of flow meters remains crucial for ensuring precise water volume management during the espresso brewing process.

by Tech Nick Lee Ahero, M. Casiraghi