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When doing this mod I wanted to keep the metal to a minimum to retain as much of the heat as possible, so I made only the bit that was under a lot of stress out of metal (brass). The rest I made out of PVC because its cheap and easy to work with.
The problem with PVC is that at 60c it has 20% of the strength it has at 25c. And Im putting boiling water in there. So, yes theres a reason I dont want to pressurise it too much. So, instead of using the normal pipe, I used the fittings which are much thicker.
That said, because the plastic is such a good insulator, the outside doesnt get very hot at all, so it retains a fair bit of strength. The MkII version might be made of a different plastic.
The main problem with the Presso in its original condition is that, for me, to get a good pour you need good pressure, and to get any volume you need to pump it more than once. Im sure this upsets the cake. The Pneu-Presso uses a smooth flow of higher pressure, and the cake is not disturbed. I was originally going to hook it up to my air compressor with a regulator, but the bike pump seems to work pretty well.
I need to do some work on a permanent pressure gauge and pressure release valve.
And I need to stop playing with it because Im drinking a lot of coffee.....
Originally posted by 594D564C54574D3F0 link=1321770018/8#8 date=1321853454
Looks AWESOME! Great job gonzo
How is the coffee tasting with the new pressure pump vs. man-powered strength?
Well, its still man-powered... unless I can talk my missus into doing it...and its certainly a lot easier on my pecs.
Anyway, Ive been able to grind a little finer, and I get better crema. Its the best tasting coffee that Ive had from the Presso to date. Another side benefit is that the portafilter had developed this tendency to undo itself when I started to work the arms. It may have been because the plastic cylinder was broken, I dont know. Now, however, it stays put.
Im still waiting for a few fittings to arrive to mount things a bit more solidly, and then Ill do some more testing, and take some more pics.
You can buy adapters designed for home beer kegging systems, but I forget what they are called. Alternatively, you can buy adapters to fit a paintball gun co2 cylinder into a regular co2 regulator - nice way to control the pressure
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