Espresso machine pumps should be connected to a water supply with a steady incoming pressure between 1.5 and 4 bars. The pressure in the water supply is called the ‘line pressure’. If the line pressure is too high, then a pressure regulating valve (PRV) should be fitted to reduce the incoming pressure to meet the manufacturer’s specifications.
The espresso machine pump adds a fixed amount to the line pressure that’s already there. This means that if the line pressure changes, the brew pressure will change, too. If your line pressure tends to fluctuate, then a pressure-regulating valve (PRV) can also help. The PRV should be set to a level at or below the lowest line pressure you get. This way, any fluctuations in line pressure will be negated by the PRV.
If your line pressure is below 1.5 bars or if the incoming flow rate is too low — for example, if the water supply passes through a narrow pipe — this can cause problems in the pump. As the water is being pumped out, the pressure upstream of the pump may become low enough that some water forms bubbles of water vapour. This process is called cavitation. When the bubble collapses again, the shock wave and resulting vibrations can damage moving parts in the pump. If the pump runs dry, it can also overheat.
To prevent this from happening in areas with low line pressure, or to safely run a machine from a water tank, the line pressure should be boosted with a pump designed for this purpose, called a ‘demand pump’. Demand pumps are typically vibration pumps, designed to pressurise water from tanks in mobile homes, and will generate around 3 bars of pressure. To ensure the espresso machine pump is supplied with enough water at this level of pressure, we recommend also fitting a pressurised accumulator tank. This will store a certain amount of water at line pressure, to ensure the espresso machine pump always has a steady supply.