yapit wrote:Thank you for all the help so far and excuse me for disappearing for a while, as i wasn't where the machine is. I kept thinking a lot about it however....
Dan, seemingly you have identified the right spot for the OPV. I got a mail from someone pointing me to this website that talks about a pressure mod for the silvia.
http://mysite.wanadoo-members.co.uk/m4tt5mith/SilviaPressureMod.html. Apparently it doesn't seem to be as convenient as the Giotto by adjusting a screw but requires an additional copper gasket to be put into. That would probably mean that there is no fine adjustment possible if i understand that right. But i haven't gone further to take it apart yet. In fact, I have no idea where to get that copper gasket if it would be the way to do....
Instead i have been thinking about the post of erics and tried to time the flow from the OPV. Well.... I am still wondering if i understood that right so let me repeat it: does zero flow at the PF mean no flow from the PF as if you would put a backflush disc in or use a PF with a gauge that does not allow any flow? If yes, that is what i tried --- but i got the problem that i couldn't observe any flow at all from the OPV !!! In fact, i have never seen anything flowing from the tube connected to the OPV. The pressure gauge at the PF needs some time to get until up around 12.5 bar but then nothing happens and after some time if falls slightly. What do i do wrong here?
Of course, besides looking just at the numbers, the taste should rule.
I never had the chance to have a good coffee before, that is a fresh roasted coffee. I had one now. A blend called Malabar Gold. While i can perceive the greatness of this blend that produces lots of crema, straight espresso gets rather sour in the cup. I have the idea that this might also be related to my pressure problem, especially as a friend praises this roast as his favorite -- but i just cannot produce a balanced shot from it.
I like to add a general question about rotary pump vs. vibration pump. The former are of course rather expensive. Are they also easier to adjust in terms of brew pressure? Would that be one more reason to get a machine with a rotary pump?
That's good that you haven't taken it apart because, in fact, you may not need to. The copper gasket for your particular machine should be available from a variety of espresso machine dealers and you could always start with whomever you originally bought the machine from. Should you eventually take your OPV apart, it would be nice to have a spare gasket on hand. While copper gaskets can be reused, it is good practice to replace.
I BELIEVE your OPV is adjustable as per Dan's previous instructions but the only way to know for sure would be to disassemble it. But I wouldn't disassemble it before I knew what the true brew pressure is and had a spare gasket on hand.
If you try to measure brew pressure simply with a gage attached to the PF and normal basket in place, you should get some leakage between the basket and the PF body. The amount of this leakage will depend upon the "seal" between these two parts. In this case, your flow is the leakage plus whatever is flowing in the OPV line.
Under normal espresso brewing conditions, you don't need a "perfect" seal between these two parts because there is essentially zero pressure on the joint - the espresso is flowing from the PF spout(s).
When you use a blind basket, you are NOT subjecting the seal I speak of to any pressure but are depending on the seal between the rolled ridge at the top of the basket and the grouphead gasket to prevent any leakage. When the blind basket is in place and pump running, you should have no leakage at the grouphead, but you SHOULD have flow in the OPV line back to the tank. That flow SHOULD be ABOUT 110 cc/min at 12.5 Bar pressure. If such is NOT the case, then something else is amiss and we will need to "talk" further.
When you use any basket other than a blind basket, attach the pressure gage, and run the pump, you should get some leakage between the basket and PF body. Depending upon a couple of factors, this leakage may very well be close to "normal" espresso flow rates - you can choose your own numbers here but 2.0 oz in 25 seconds is certainly not unreasonable. If this is the case with YOUR machine, then your true brew pressure is 12.5 Bar as you measured.
BTW, I would disconnect and put a small piece of electrical tape on the heating element wires while doing all of this experimentation to simply avoid getting splashed with hot brew water.
You said "Of course, besides looking just at the numbers, the taste should rule."
Absolutely, positively, let there be no doubt that this is CORRECT.
That, by itself, should not be on a "list of reasons" to get a machine with a rotary pump. Espresso machines which have rotary pumps are high-end prosumer/commercial machines which are a cut above what you have and many cuts above what I have. But, as I said before, it appears you have quite a gem and I'm pretty happy with what's on my countertop although I do have this strange Brewtus itch that comes and goes.
Eric S.
by yapit on Thu Aug 25, 2005 3:06 am 
. I've recently upgraded from my rancilio silvia to a rancilio Epoca.
