Yes, that's one way of putting it.

If you look at the brew pressure gauge of some plumbed-in machines, they will be at line pressure whenever the pump isn't running (assuming there's no solenoid cutoff). The pump doesn't engage until the end of the stroke and raising the lever halfway will allow water to flow under line pressure. That is, water is still coming through the same pathway (i.e., through the pump); in one case it is "passive" from line pressure, the other time it's being driven by the pump's vanes.

Obviously the temperature of the incoming water is the same in both cases. This is part of the original E61 design intent. I understand some cafes used a tank on the second floor to provide the static pressure... I think that Schomer describes this setup in his book.

malachi wrote:Actually, you need stability in pressure and stability in temp.

Keeping in mind that in our little coffee world, the word "stability" remains ill-defined.

Some folks think stability means that the average temperature and pressure of each shot is the same within a certain tolerance. Schomer says temperature stability means a ruler-flat temperature curve throughout the extraction. Other folks want to see the particular "profile" (rising or falling curve) of temperature and pressure to be the same for every shot. Recently malachi went a step further and theorized that 60-120 hz pressure pulse vibrations during an otherwise perfect pressure profile might be detrimental.

There are different definitions of "stability."

HB wrote:I've not done a side-by-side comparison of rotary versus vibration pumps. But given the care Jim and Ken put towards attempting to discern a difference while finding little, I'm doubtful it's a worthwhile consideration for your average home barista except for the quiet it affords.

Nothing in espresso is EVER settled with one test. In this case, Jim proved that the espresso made by one vibe-equipped Cimbali Junior wasn't significantly different from the espresso made by a different, rotary-equipped Junior. This was a really neat experiment, but we shouldn't regard it as a universal proof.

Abe Carmeli wrote:The preinfusion chamber works well with a vibe pump, but once you convert to rotary, it will go to max pressure in about 2 secs. A little too fast for real preinfusion.

The preinfusion for the Microcasa is all manual; I wait ten seconds during which the brew pressure is 1.2 bar. The E61 vibration pump machines I've tested reach max pressure in six seconds, maybe a little less. The three rotary (non E61) machines I've looked at closely (La Spaziale S1, Cimbali Junior and Elektra A3) rocket up the pressure in a few seconds; droplets are forming in four. The Lineas I've tried behaved similarly, i.e., the pour starts long before it would for an E61 / vibration pump.

And yet the extractions from the A3 are sooooo-o-o much easier than other rotary pump machines I've tried, and the only thing I can point to is the effects of preinfusion. Hey, that's only three seconds... how'd it happen so quickly and effectively? This observation is forcing me to rethink the importance of the length of the "preinfusion pause", a thought which leads me to a concrete question:

• What's the programmed preinfusion delay for the Synesso Cyncra?

Background: I briefly used the Synesso Cyncra in the BGA booth at the SCAA conference in Seattle. As I understood it, you had the choice of a manually selected preinfusion delay by pushing the pump switch halfway across, or a programmed preinfusion delay by pushing it straight across. It seemed like the pour commencement times were consistent with other commercial machines, but like I said, I only used it briefly... Chris or other Synesso fan, would you fill in the details?

cannonfodder wrote:Now as Framey stated, $350 for a rotary pump, plus added mods/plumbing to the existing machine quickly makes this an unwise modification.

it's not nearly that expensive to do. off the top of my head, it should be around $150.

barry wrote: it's not nearly that expensive to do. off the top of my head, it should be around $150.

I am in a middle of a rotary conversion now. Small pump & motor will cost ~ $200-250.00. Tubing, fittings, line pressure regulator, gauge, valves ~ $70-150 depending on options you chose.

Abe Carmeli wrote: I am in a middle of a rotary conversion now. Small pump & motor will cost ~ $300.00. Tubing, fittings, line pressure regulator, gauge, valves ~ $70-150 depending on options you chose. If you go with a commercial machine pump and motor, add another $200.00

i suggest you consider different equipment sources.

Abe Carmeli wrote:The preinfusion chamber works well with a vibe pump, but once you convert to rotary, it will go to max pressure in about 2 secs. A little too fast for real preinfusion.

This is not a true statement for all E61 rotary pump machine.
When I adjust the pressure on my Lyra the pressure starts off slowly and increases in speed until it reaches 130 psi. This action takes about 7 to 9 seconds, if memory services me correctly. I am not using a cheap gauge. My current set up is an Ashcroft test gauge. http://www.ashcroft.com/products.cfm?doc_id=117


Is this not preinfusion?????



Tom

FXDXT wrote: When I adjust the pressure on my Lyra the pressure starts off slowly and increases in speed until it reaches 130 psi. This action takes about 7 to 9 seconds, if memory services me correctly.

My experience matches Tom's exactly. I can't say if this is a pre-infusion because the pump does engage instantly, but I can say for sure that it takes several seconds for pressure to start building. Once the pressure begins to build then it ramps up very quickly.

HB wrote:The three rotary (non E61) machines I've looked at closely (La Spaziale S1, Cimbali Junior and Elektra A3) rocket up the pressure in a few seconds; droplets are forming in four. The Lineas I've tried behaved similarly, i.e., the pour starts long before it would for an E61 / vibration pump.

This is easily fixed with a gicleur (orifice) downstream of the pump. Most people use 0.6-0.8mm). Bill Crossland from ESI said that the automatic Lineas shipped without gicleurs, but the semiauto Lineas generally had them. Presumably this was because if you were a semiauto barista, you cared.

On my rotary Silvia I used a 1/8" needle valve rather than a fixed orifice. This allows me to adjust the length of "preinfusion" to just about anything.

Dan, what is it about the A3 that made its "preinfusion" different from the others?