I have read a lot of post to be able to found the reply to following question :

Which flow rate (in ml/mn) is required for the pump function in an espresso machine ?

Simple question (for me) but a lot of different and or divergent answers.

So could you help me to found some typical values to associate with :

- Maximum flow rate of pump (manufacturer data, given as a limit for the product. I think this corresponds to the max flow without any charge on the output).
- Average/Typical flow rate for an extraction (when no profile is used and when 9 bar goes on puck).

I note from posts : pump max flow of 650 ml/mn (650cc/mn), 250ml/mn during extraction at 9 bar against 100 ml/mn for certain persons as optimal flow rate ???

Jean-Marc,

Maximum flow rate is generally called out by the pump manufacturer and is related to how quickly the pump can fill an empty boiler. My old Rancilio S20 had a 200LPH pump which is 3,333ml/min

Such a flow rate is rather typical for a rotary pump that is sized to keep up with running multiple groups and keeping a large service boiler topped up, but is completely overkill for when it comes to "optimum flow rate" for espresso.

Vibe pumps tend to live in the 650ml/min range at free flow (zero back pressure) and the pressure falls precipitously as the pressure increases. By the time you get to 9 bar, the pump output has dropped to roughly 260ml/min:


However, don't be confused into thinking 260ml/min is "optimal" for brewing espresso. It is far too fast, even for EKspresso, where you might be extracting 60ml in 20s.

Actual flow rate during a non-profiled shot is still quite varied. The flow starts at whatever the water debit of the machine happens to be (pull a flush into cup for 10s and see what the flow rate is to find out) and then slows down until the dwell point. For a typical vibe pump E61 machine, this might be 5ml/s when you start the shot (300ml/min, less than 9 bar on the brew gauge) while the headspace fills and then drop to 0.5ml/s (30ml/min) as the first drips emerge from the portafilter. Once flow starts, shots tend to slowly build in speed, going from 0.5 to 1ml/s then up to 2 or 3ml/s at the end of the shot, depending on the puck integrity, solubility of the coffee, type of grinder, etc...

The average flow rate for a typical 30ml shot pulled in 30s is of course 1ml/s or 60ml/min, but since the flow is so restricted around the dwell point, you can see that a range of pump outputs is necessary even for the most basic pump machine. The pump always operates "on the curve" so any time the output from the portafilter is less than what the pump curve suggests for a given pressure, the difference between the actual flow into the cup and the pump output (as shown on the curve) is vented back to the reservoir through the OPV. This is how you can set a maximum brew pressure and achieve varying rates of flow from a pump "rated" for 650 ml/min.

Hope this helps,

Cheers!

- Jake

Jake's reply is about as good of an answer as you can get.

Thanks Jake you are my favorite professor

« Rancilio S20 had a 200LPH pump which is » is 200 liter per hourly ? An error in your post or a real karcher !

As I understand your explanation, important data for pump flow requirement are :
- Around 300 ml/mn at beginning
- drop at 30 ml/mn when puck infuses
- increase to 180 ml/mn during extraction to the end.

So if you take these data to select a water pump adapted to a coffee machine use, you chose a pump with a water flow max of 700 ml/mn as a minimum and 9 bar capabilities. Is this correct

If yes, it is not necessary to select water pump with more important water flow. So why rotative vane pump as fluidotech have really more high flow capacity ? It'oversized...

For a not professional user, is it interesting to use rotative pump on a water tank in this home espresso machine ?

Sorry but what is Dwell point exactly ?

Jake it's perfect. Thanks.

« It was oversized, but not a problem as the pumps are designed for near continuous duty at full bypass » how a such system works ?

In practice with oversized pump and full bypass + continuous run, how could you adjust the output flow rate (for flow profiling) ?

Perhaps it could be more easy to avoid the bypass, and to control rotation of pump through a VSD. But I have no knowledge in how will be the flow delivery with this type of pump if you drive it by PWM control.