A new espresso machine just arrived or the machine that has been giving years of espresso service has just experienced pump pressure problems. We find that most of the time that it is not actually the problem with the pump. But, let us start with some basics. Another common word for gauge is manometer, and these gauges typically read up to 12, 14, or 16 bar.
In many cases, an espresso machine can have a brew pressure gauge or a pump pressure gauge or both. Let us define these into a little more detail…
Brew Pressure Gauge
This gauge usually measures the pressure of the resistance of the ground espresso coffee in the filter basket when the pump is engaged. This gauge is usually found on vibration pump espresso machines as vibration pumps usually try to create enough pressure to overcome the resistance. The vibration typically needs 7-9 seconds after the pump is engaged to get up to full pressure. The maximum pressure is also regulated by the over pressure valve or also known as the OPV.
The resistance is created by the fineness of the grind, the amount of the coffee in the basket, and the tamping pressure. All are relative to creating a good espresso beverage. The brew pressure gauge is a good feature found now on most espresso machines. However, it is not a good tool because many newbies read the gauge when the machine is not extracting. In this last case, this gauge has no relevance unless the vibration pump espresso machine is directly plumbed to a water supply. In this direct plumbed case, it can or may show the water line pressure. However, not always. On tank versions, it can show the pressure of the heat exchanger or heated boiler in an espresso machine.
The brew pressure gauge can be used to see that the vibration pump works. Usually, a dead pump will not pump at all. If a brew pressure gauge is not reaching 8-9 bar pressure, then the resistance in the ground coffee in the basket is the problem. Otherwise, it can be the over pressure valve is faulty. To test, a blind filter basket or insert needs to be inserted into the portafilter which is then locked into the grouphead (you can only do this on machines with a 3 way valve on the grouphead). If the pressure goes up to 8 bar or higher, the over pressure valve is ruled out and everything points to the grinder, the amount of coffee in the basket, or the tamping pressure.
In over 95% of cases where the espresso machine is blamed for a bad pump, it is actually a grinder problem or an espresso preparation problem.
Pump Pressure Gauge
This gauge is usually found on espresso machines that have a rotary vane pump. This gauge only monitors the pump pressure and not the resistance from the ground espresso coffee in the filter basket. The ramp up pressure of a rotary vane pump is almost instant. On direct plumbed models, the pump pressure gauge usually will show the water line pressure. The aforementioned blind filter test can be used to determine if the over pressure valve is faulty. This gauge should also not be looked at unless the pump is activated.
Espresso Machines with Pump Pressure Gauge and Brew Pressure Gauge
Recently, there are machines that have a pump pressure gauge to monitor the pump pressure of a rotary vane pump and a brew pressure gauge installed on the grouphead to monitor the resistance allowed on the ground espresso coffee. The brew pressure gauge is needed on the grouphead on espresso machines that allow the operator to control the flow or pressure of water into the filter basket. The Lelit Bianca is an example of this.