Hey David, yeah I'm sure it's over-size, but the standard is 1 mm and it's not THAT oversize As any machinist/tool maker will tell you, a drill makes a hole that is neither on size, nor round for that matter, however most of the time it's not that important. I did measure the drill bit with a micrometer but can't recall what it was off the top of my head, I recall it wasn't exactly 0.6 however. Even if it went out to 0.65 that's good enough in my book as the absolute value is immaterial just that it's smaller than standard.

As it happens I'm up for a new pump anyway. I was able to get 9 (or even 10 Bar if I wanted it) out of the pump and it was solid at these pressures. However I could only get it with a high inlet pressure (600 KPa). This was the configuration I've been testing it with until now. Once the 350 KPa pressure limiting valve went in on the inlet I'm only able to get 7 Bar out of it. I thought it may just need a lube of the adjustment plunger's o ring but nope, seems she's cactus unfortunately. Oh well.

Pete -

There's plenty of Bezzera experts in Australia - at least that's the feeling I get when I peruse:

http://www.coffeesnobs.com.au/

Why not confirm what pump is "supposed" to be in this machine and revert back to the original Bezzera gicleur (1.0 mm) and then play from there? Those gicleurs should be relatively inexpensive - maybe not readily available. It SEEMS to me that the pump you have is one notch above what is supposed to be in there and that one notch is, at least, trying to flow 40% more (35 gph vice 25 gph rating). BTW, Procon's (and everybody else's) flow numbers are based on an inlet pressure of ~ 0 psi and with the pump bypass blocked in the closed position.

That really high inlet pressure (6 bar) you were running to achieve the ~9 bar brew pressure can wreck havoc on the boiler fill valve.

Here's a set of curves of pressure drop as a function of flow for various gicleurs - the MS Excel file is, as always, available on request.

Thanks Eric, I'm not sure how it is over there, but here the spare parts distributors sell just one model of replacement pump.

I finished up ordering a replacement directly from the Bezzera agents, but once again it was the one pump to do all their machines.

I'll see how it all goes.

Pete

PS Nice graph btw. I was thinking however that based on a standard 60ml/30 sec double shot the flow rate is 2ml/sec, so based on your graph the pressure drop is actually quite small indeed until you start going under 0.6mm

Of course, we wouldn't want to forget about the water that did flow but remained behind in the spent puck, would we?

The weight of the water is pretty darn close +/- to the weight of the grinds. While I have measured to some extent, these guys took it several cuts above in section 4.3 : http://www.home-barista.com/revie...perature-t516.html

Oh yeah sorry, forgot about that, trying to do a billion things here at once. I just measured the volumetric dosing then and in total it's roughly 80ml for 60ml shots. So 2.6ml/sec or SFA difference in other words. I was guesstimating a 0.5 bar drop for a 0.6 mm gicleur. To be honest I'm not sure where I pulled that figure from, or if I did know, you probably don't want the specifics However from your graph the difference between the 1.0 and 0.6 looks like about 0.5 Bar, so that seemed a good guess, and I had the pump adjusted up 0.5 Bar to compensate.

With the pump I also ordered a genuine 1.0 mm Bezzera Jet, so can always stick that in if required. I also like the idea of going back to standard if it all goes a bit screwy. However the 0.6 mm is definitely giving good (or better anyway) pre-infusion effects, and the ramp is very clear on the pressure gauge. Just in principle I like the idea and will leave it in for now.

I left the 350 KPa PLV on the inlet (as was always the intention) so until the new pump arrives I'm left with brewing at 6-7 bar Kids, don't try this at home, it produces REALLY ordinary shots. Ironically not dissimilar to many I taste at coffee outlets Fortunately I have to go away for work so the pump should be here when I get back and hopefully I can finally put the covers back on this baby for good!

Pete