Understanding VBM E61 group pre-infusion
I've been trying to understand the process of pre-infusion which the VBM E61 group-head uses and was hoping for some thoughts from those more experienced with it.
Having bought a used VBM fairly recently, coming up to speed has involved doing my own servicing (replacing E61 valves, seals etc) and searching online for answers. As usual there's some conflicting information to sort through.
Reading between the lines, it seems that pre-infusion occurs in the following fashion. When the E61 lever is moved up to the brew position, the brew valve opens & the pump starts to fill the chamber above the infusion valve and then begins to pre-infuse the coffee in the portafilter. When pressure reaches 4-6 Bar (controlled by the infusion valve spring), the infusion valve opens. The 4-6 Bar pressure is maintained until the infusion chamber is filled. Pressure then rises to full brew pressure (around 9 Bar controlled by the OPV) and held there for the duration of the shot.
This all happens in a matter of seconds of course but seems to be the main process of pre-infusion in E61 groupheads as best as I can make out.
Am I on the right track or is there something I've missed? Any thoughts?
Last edited by CafeLotta; 17th January 2018 at 07:32 PM.
I think you are right on the money. The E61 group is often praised for its thermal characteristics, but from what I read the main selling point and the essence of the original patent is the pre-infusion feature as you have paraphrased it.
Originally Posted by CafeLotta
Some people use the brew lever in its middle position for pre-infusion, but unless the machine is plumbed in, so the coffee can be pre-wetted at the water mains pressure, I would leave that option out.
I have read this also but don't really see the point. The E61 and its inbuilt form of pre-infusion seems to be a proven thing if maintained correctly. This should include changing the spring on the infusion valve at a full service I believe.
Originally Posted by degaulle
Strictly speaking, what I refer to as E61 pre-infusion is just a characteristic of the E61 brew cycle and not the commonly referred to form of pre-infusion of wetting the puck before beginning the brew cycle.
Last edited by CafeLotta; 17th January 2018 at 07:30 PM.
Came across this discussion which includes the original E61 patent details (both diagram and text later on).
Original design was for 1.5 bar pressure required to open Infusion Valve not 4-6 bar as I surmised in my original post.
Thread re: E61 temp stability