The pre-infusion feature which is common in high-end machines prepares the coffee puck in the basket just before the brewing by delivering a small amount of water, enough to just wet the coffee cake prior to brewing. This technique is said to improve the shot taste.

To be honest, I tried it manually few times in Silvia but didn’t notice any difference in the shot taste.
Anyway, since I was deeply into this project, I also added this feature.

Unfortunately, the timer that I used does not have this ability. It might be possible to change its software to do so but this is beyond my knowledge.
Getting a controller that is capable of doing pre-infusion meant additional $250 that I was not willing to spend.

So, I decided to do it manually with the help of a simple momentary push-button switch.
Silvia brew switch that operates the pump is a rocker type switch. This kind of switch is not meant for short momentary operation. Timer mod is already taking control of the switch, so all was left to get the pre-infusion function was to add a momentary
push-button switch. I added the button to the control box and connected it to the timer controller output.

Each momentary push operates the pump for a very short time and few quick clicks make the pre-infusion effect. Yes, I know this is a kind of degradation with all the controllers around, but at least I have it in case I want to use it.
Eventually, I use it rarely. As I wrote above, I personally do not find any improvement in shot taste with this function on Silvia.