I designed and built a preinfusion timer for my Rancilio Silvia that uses a pump control technique similar to that used in an old Krups espresso machine I had. Vibratory pumps will respond to as little as a single line cycle, which allows for control of flow rate by pulsing the pump at a lower rate than line frequency. The Krups machine hit the pump every eighth cycle in steam mode to limit the flow of water to the thermoblock. My design defines a 12-cycle period (200 ms at 60 Hz) with a selectable duty cycle of 2/12 to 6/12 during a ten second preinfusion interval. The duty cycle is set by a selector switch, which has additional positions to select OFF and four time intervals for conventional preinfusion (pump on, delay, pump on).

The hardware was implemented with a PIC microcontroller driving a triac. The circuit is installed inline with with the Silvia pump drive signal (two wires in, two wires out), so installation is a snap. One disadvantage is that the preinfusion delay is also active when the water dispenser switch is activated. I suppose that Rev A will incorporate an input from this switch to enable full pump power for water mode.

I look forward to experimenting with preinfusion. Hopefully it will make is easier to hone my grinding, dosing, and tamping skills, which really stink at the moment.

What am I missing here?

A vibe pump when used in an espresso machine, by its very design, preinfuses. It takes 6 or 7 seconds to get up to full pressure (presumably around 9 bar with an OPV). That is very nearly ideal in the view of most "informed" people whose opinion I have ever read on this subject.

What it is it that you hope to improve in the flow and pressure characteristics of this very much unloved type of pump which nonetheless seems to have a very attractive pressure profile?

ken

ethorson wrote:I designed and built a preinfusion timer for my Rancilio Silvia that uses a pump control technique similar to that used in an old Krups espresso machine I had.... I look forward to experimenting with preinfusion. Hopefully it will make is easier to hone my grinding, dosing, and tamping skills, which really stink at the moment.

Thanks for sharing your modification. For those who want to experiment but don't want to tinker with hardware, see Don's Rancilio Silvia Preinfusion Technique, summarized below:

vanboom wrote:1. grind, tamp, etc.
2. place a pitcher under the steam wand
3. set the steam valve slightly snug (allowing some water to flow at a very slow rate out of the steam wand)
4. lock in portafilter
5. press the brew switch: listen to the sound the water is making through the machine
6. tighten the steam valve a second or two after you hear the puck fill (yes, you can HEAR it)
7. finish extraction

Ken Fox wrote:What it is it that you hope to improve in the flow and pressure characteristics of this very much unloved type of pump which nonetheless seems to have a very attractive pressure profile?

Unloved? Once the problem of noise is addressed, vibratory pumps are very lovable.

Eric -

Great mod - nicely engineered. Silvia's internals look very well laid out. Here's one that does it hydraulically:
http://www.coffeegeek.com/forums/espres...ods/373954

On further thought I think what you are getting at is that the Silvia is not the easiest machine out there to get a good shot out of. This has been noted many times in many threads here, before.

While it is possible that modifying the machine will improve the percentage of acceptable shots that you get, nothing short of replacing it with something else will yield better shots, both on a percentage basis and on the comparison between the best shots you can get with a Silvia and what you could get with something else.

My advice to anyone else considering significantly modding this machine would be to resell it (as it tends to have a good resale value) and investing the funds into something clearly better, like, for example, a low end E61 HX machine.

ken

Ken Fox wrote:What am I missing here?

A vibe pump when used in an espresso machine, by its very design, preinfuses. It takes 6 or 7 seconds to get up to full pressure (presumably around 9 bar with an OPV). That is very nearly ideal in the view of most "informed" people whose opinion I have ever read on this subject.

What it is it that you hope to improve in the flow and pressure characteristics of this very much unloved type of pump which nonetheless seems to have a very attractive pressure profile?

I undertook this project because I was aware of many other posts on adding preinfusion to the Silvia. Whether it is effective in improving my espresso extraction is yet to be determined.

At any rate, you got me fired up to actually do some measurements of pressure vs. time. I drilled a hole in a spare backflush PF and plumbed in a compression tester that I had laying around. I added a sponge to simulate the coffee puck and loosened the connection to the gauge to let some water escape during the shot. The tests show that the pressure reaches maximum after about 3.5 seconds without preinfusion vs. 10 seconds with preinfusion. For both of these test runs I made sure that the boiler was completely full. Obviously the time at low pressure will be extended if the boiler is not full.

My experimental setup and a video of the tests are shown below.

It's hard to tell, but it seems that pulsing would destroy the puck by the way the needle is bouncing?

Do you have a video of the actual flow from the grouphead with your pre-infusion mod?

I am very jealous of everyone having the ability to do mods like this.

While that is a slick modification and a testiment to your controls skillz, I don't see any advantage over the VPT, and more importantly as someone else mentioned, it might destroy the integrity of your puck. When you flow water into the steam wand, does it cause alot of turbulence in a cup of water?

It also appears you should adjust your OPV, as you're running around 1 bar too high (assuming the flow is proportional to a shot). I set my OPV to about 9 bar with some water leakage.

JBSmoovee wrote:While that is a slick modification and a testiment to your controls skillz, I don't see any advantage over the VPT, and more importantly as someone else mentioned, it might destroy the integrity of your puck. When you flow water into the steam wand, does it cause alot of turbulence in a cup of water?

It also appears you should adjust your OPV, as you're running around 1 bar too high (assuming the flow is proportional to a shot). I set my OPV to about 9 bar with some water leakage.

I agree that VPT can give equivalent or better preinfusion performance with a skilled operator. I just like to tinker. The pressure variation does not seem to mess up the puck as my shots do seem to have less channeling with preinfusion turned on. Perhaps the situation will improve more when I get the pressure adjusted correctly. My Silvia does not have an adjustable OPV so I am going to make some washers to try and get things right.

Out of curiosity I ran a pressure test on my rotary pump machine, a Bezzera BZ35. It does not have an E61 group or preinfusion.