Basics of lever operation

Jeff Kinzli

Hey All, I'm pretty comfortable with how my Profitec HX machine works and I've become relatively competent pulling decent shots with it.

I'm about to order a Londinium R and have to admit I don't quite understand the process of how to make espresso with a lever machine.

I think you pull the lever, which starts the pre-infusion process, and then at some point you push the lever back up which then allows water to flow.

I wonder if anyone has seen any videos anywhere that show the process and explain what is happening at each step, and how varying the time that the lever is up/down will change the output.

I'm awaiting my new Monolith Flat SSP grinder any day now and hence it seems its time to get the LR to go with it.

Any thoughts, suggestions for videos, or otherwise to help a lever-n00b?

Thanks.

Reiss Gunson

hi jeff

thank you for your question

just like any espresso machine the dosing and distribution of the portafilter is important if a good extraction is sought

the dosed portafilter is locked into the group in the same way as a pump driven machine

the lever then needs to be pulled down immediately, just like any other machine, otherwise the heat from the group starts to degrade the coffee

lever machines are also referred to as piston machines, and this may confer a better understanding of how they work; when the lever arm is pulled down the connecting rod is raised which being connected to the piston also lifts the piston

four holes set at ninety degrees in the sleeve of the group (behind which lies a water jacket) allow water to enter at pre-infusion pressure as the piston seals are raised up over these inlet holes

the pre infusion pressure determines how quickly, how hot, and how much water enters the brew chamber as it rushes from the higher pressure of the thermosiphon-heatexchanger circuit that it has been held at when the piston was in the down (resting) position, to the lower pressure inside the brew chamber (which is the space below the now raised piston) in order to equalise the pressure throughout the now combined volume of the thermosiphon-heat exchanger and brew chamber. in doing so the water rushes up not one but both thermosiphon pipes from the heat exchanger and into the group, destroying the thermosiphon loop as it does as the pressure equalises in both thermosiphon pipes as a result and it takes just the right amount of time for a pressure difference between the two pipes to re-establish itself after each shot is pulled; this is the key to our machine having such exceptional thermal stability

once the pressure in this new combined space is equalised the water is pushed down into the dry coffee puck at the pre-infusion pressure set for the system

the pre infusion pressure will push this water right through puck, saturating it, and then a drip will fall from the bottom of the portafilter basket indicating that the puck has been saturated

the assumption in the above description is that you have taken care with the distribution of the coffee grounds throughout the puck prior to tamping them down, such that not channels exist in the puck for the water to find and rush down. this is known as channelling and describes chronic under-extraction down the path of the channel as a result of high water flow at low pressure down that channel, and little/no extraction from the rest of the puck as the channel provides the path of least resistance through the puck and so the water avoids going through the rest of the puck

anyway, lets assume the extraction was good and the first drip has fallen in the cup; this is the signal to raise the lever arm up out of the cam lock that is holding the lever in the down position and allow the expanding spring to drive the lever arm up until its upward travel is arrested by the brew water below the piston meeting the resistance presented by the puck underneath. at this point you can remove your hand from the lever and the machine regulates the extraction from that point forward, which is why spring lever groups deliver more consistent results than manually pulled lever groups

whether you decide to leave the cup under the group to catch every last drop, or to pull the cup from the stream of coffee is entirely down to the style of shot the operator of the machine is seeking

i think that is about all there is to it

kind regards

reiss.

Jeff Kinzli

Reiss, thank you for your detailed answer. I will read through it a few more times to make sure I understand.

I've heard of people leaving the lever down for varying times in change the dynamics of the espresso.

For some reason I had a vision that pulling the lever down forces the water into the puck, which is clearly what is not happening. It seems to me that the entire extraction is regulated by the pressure/temperature of the boiler, and when the lever arm rises, it is essentially cutting off that boiler pressure from the puck at some linear (?) rate determined by the spring.

I guess my last question is that this system has an upper limit on the amount of water that is allowed to enter the brew chamber - I assume that this volume of water is probably much higher than a double shot would require even if a luongo shot was called for. Is that the case, or is this a variable of how long the spring is allowed to stay in the down position?

Thank you again - I appreciate the basic explanation and look forward to having this machine in my house very soon!

Reiss Gunson

hi jeff

you are right, but you have both first and second order lever designs - the group we use being a first order lever and something like a la pavoni/cremina group being a second order lever from memory (where the fulcrum is at the far end of the lever and the load is at some point along the lever between the fulcrum and the effort being applied at the other end of the lever)

you are correct that pre-infusion pressure occurs at boiler pressure in a dipper and also open themosiphon design, but not in a closed heat exchanger (HX) design where the group is being supplied with water from an HX chamber that is completely isolated from the boiler - this allows us to maintain a different (almost always higher) pressure in the pre-infusion circuit than in the boiler itself

the pre-infusion pressure phase on the pucks ends when the lever is released to the extent that it causes the piston to come down sufficiently that the piston seals close off the four inlet holes in the group sleeve and the pressure of the spring takes over applying pressure on the water, which in turn presses down onto and through the puck

all piston machines are fixed volume by definition, assuming additional strokes/part strokes are not performed, and in the case of the group we use it is 60mL

kind regards

reiss.

Jeff Kinzli

Thank you again, Reiss, much appreciated.

Given that 60ml is the maximum water amount, and some is left behind in the puck, that means that a double shot (in the US 2 ounces) is pretty much the maximum espresso volume that can be output. If one wanted a larger espresso volume - like a double luongo, would you then pull the lever down the first time, allow it to rise, and pull again after the initial pull volume was exhausted? Is this routinely done? I typically make larger milk drinks (lattes mostly) and usually do a relatively largish double shot.

I think that's the last question

Reiss Gunson

sorry, 60mL is the maximum you will get in your cup.

you make it stronger by using a bigger basket in order to use a higher dose of coffee, not by pushing more water through the same dose.