Now that I have a machine to get up clean and running, I have started consider Subject line issue. I think a list could be useful to others. Is it possible to mod earlier design machines like mine or Almico's Argenta to have pre-infusion? adjustable preferably.

What I have noted on other threads and discussion:

1. design with e61 group. Pre-infusion is said to be part of the design.

2. Install a delay circuit (adjustable if possible) between solenoid opening and start of pump pressure. Thereby line pressure serves as preinfusion. This was mentioned on threads about Elektra machines.

Other methods?

On a vibe pump machine, add a dimmer, variac or micro-computer.

Add a gicleur or needle valve.

Simple, delay on make relay inline with the pump power provided you have the machine plumbed in. The mains pressure does your pre infusion.

In a Conti Monaco (Club is the one-group version) manual it states that the large cup programmable buttons have no pre-infusion, only the espresso buttons:

Attention :
Seules les 1TE et 2TE ont une pré infusion.
Warning :
Only the 1 and 2 espresso cup pre-infusion

At least, that is how I interpret this brief hint to pre-infusion, the only one I see in the manual.

I don't know how that works, but it gives me a way to compare a pre-infusion shot to a non-preinfusion shot, dialed in otherwise equally.

I just had an active preinfusion mod on my ECM Veneziano (E61 HX rotary pump). My machine was really bad, because it has programmable buttons, so no middle position on the lever (since there is no lever...), the 9 bar pressure built up damn near immediately. The guy, who did it, added an additional OPV with a 1mm flow restrictor to get it down to around 2,5-3 bars. It uses a delay on make relay, built in under the driptray for easy access. You can adjust your timer to your coffee of the day (I time it until the first drops appear, the puck is fully saturated). So far it works really well. This is how it look inside:




This is how it works:
http://www.youtube.com/watch?v=3T1h5tXs3KA