peacecup wrote:My Caravel shots on Friday were quite good. A new O-ring for the piston center hole, and some Dow 111 from Greg seems to have helped to increase brew pressure a little.
In my experience so far I find that the shots blond towards the end of the pull no matter how I grind/dose/tamp. The flow usually slows to a fast drip and begins to blond towards the end. Anyone had any experience with this, and found a solution?
Also, what temperature are you Caravel users pulling shots at? Full rolling boil, pre-boil, post boil? I have yet to even put a thermometer it the boiler or brew water, but plan to do so soon.
I've found that the Caravel PF is just 1-2 mm smaller diameter than that of the Ponte Vecchio. In fact, the OD of the baskets are the same, the ID diameters are what varies. This got me thinking that a new Ponte Vecchio group head gasket might fit the Caravel, and I'm anxious to try this. DUring very hard pulls on the Caravel I get a few drops of water escaping over the PF, which suggests a new gasket is in order.
The piston is very narrow, as is the basket. So you don't need to pull very hard on the lever to get good brew pressure. Pressure, as you know, is force divided by area; the smaller the area, the greater the pressure.
Given the blown gasket, and the blonding, and your statement that you use "hard pulls", I would guess that you're pulling too hard, and that this is the main reason you have blonding. You could be pulling at 11 bar or so. Again, the smaller piston translates the force into greater brew pressure.
Try a gentle semi-pull to preinfuse and then lift lever to get more water, and then press down firmly but not "hard".
I have tasty shots with the kettle water temp at 205F, after several warming flushes.