It's possible that your over-pressure valve is installed downstream of your flow-meter and set to a low enough pressure that it's opening during a normal shot, but not during a gusher shot (in general, the higher the flow, the lower the pressure). If that's the case, that may be where you're 'losing' that extra ounce of water. If you have a vibe pump Junior, that may be entirely normal (though kind of stupid, the OPV should be upstream of the flowmeter for just that reason). If you have a rotary pump Junior, you need to set the OPV to 11-12 bars and use the pump to regulate brew pressure. It could also be the 3-way valve as we mentioned.

Like you say, the excess water has to go somewhere, and given the amount it's unlikely it's a puck absorption differential. The only real way to know where it's going is to look...

I would also humbly suggest that when you have the 15-20 second gusher, the set volume is not correct for a proper pull. The water is not going to the grounds and building a cushion above the puck at the proper pressure. It's racing through to the cup.

Since there is a volume of water you've found with the proper grind which yields a proper cup, seems like you're chasing a problem which doesn't really exist. Lose the earlier volume setting for a double, it's wrong for you, your machine and your coffee.

t3steve wrote:Let me try to re-state what I have already said.

I can set the grinder and manually operate the espresso machine to dispense a good tasting 2oz espresso in 25-30sec using a 30lb tamp pressure.

Dan Kehn says in his review of La Cimbali Junior DT1 that "set the volumetric dose to 90ml or 3oz to get a 2oz shot (note the extra 30 milliliters above the volume of a standard double accounts for the water absorbed by the puck and the space above the dispersion screen)".

When the grind is too coarse and a 2oz shot is dispensed in 15-20sec then the 90ml water volumetric dose is correct.

When the correct grind is used as determined in the first step above the, water volumetric dose required is around 4 to 4.25oz to get a 2oz espresso.

Now if the extra 30 milliliters above the volume of a standard double accounts for the water absorbed by the puck and the space above the dispersion screen) does not change the extra 1oz of water must go somewhere right?

Steve

I don't question the conclusion that excess water, if there is any, must be going or staying somewhere if it doesn't show up in the cup. But I have three questions; sorry if they're very basic; when troubleshooting remotely it's best never to assume:

1. Are you certain that the 4oz setting is actually dispensing 4oz gross? You've measured this?
2. How do you know the gross water volume required for 2oz net when operating the machine manually? You are using temporal-units for manual mode and volume-units for auto mode.
3. Are you certain that your coffee dose and tamp are consistent when comparing manual to auto mode?

With respect to #3: I'm suggesting that you remove one variable from the comparsion (compaction) just to make sure that the additional ounce+ of water (vis-a-vis Dan's review) that your machine is alleged to require is not the result of the coffee being too densely compacted and/or overdosed. When comparing manual to auto mode be certain to get the dose the same. It doesn't take much difference to make a difference.

I read the vibe pump faq's as suggested and understand now that vibe pump flow rate is much greater than can be used so some is dumped by the overpressure/expansion valve. I guess I thought it would be routed back to the doser chamber to preserve shot volume.

The 3way valve is also not working properly. the group head leaks in between shots and does not open to bleed off pressure after the shot. When cleaning with the blind portafilter it does not release pressure at all and it is extremely difficult to remove the portafilter.
I am going to try to make time this weekend to remove the 3way valve and try to clean/diagnose the problem.

Another problem I have is that only two of the positions work on the dose selector. Does anyone have experience with this problem? I am going to have to figure out if the problem is the four position rotary switch or the wiring to the control rods or something else.
Any suggestions?

Steve

I still say that the symptoms you are describing are pointing toward the 3-way valve being stuck and that a few repeat detergent backflush could possibly fix it.

Have you tried a few detergent backflush one after the other? Do not hesitate to let the detergent sit in there for a while after the pump stops. Let the detergent work it way through whatever may be blocking the 3-way valve.

Yes I detergent back flushed the heck out of it last weekend. I am going to try disassembling the valve this weekend to clean it. Unfortunately I can't dedicate very much time to working on it.

Steve

t3steve wrote:I am having trouble adjusting the shot time. I am using an old La Cimbali D and a Super Jolly with new burrs.

Could not it be that you have new burrs that introduce inconsistency because they are not yet fully set? What about wearing them down a little bit (how many pounds of coffee? anyone?), and experiment then? Just a suggestion.

Just to make sure, when you attempted the backflush, you ran the pump for about 15 seconds then turned the machine off for 15 for few cycles, right?

I'm going with a stuck 3-way, either through gunk or failed parts. My memory is that the 3-way defaults to open (draining) until it gets power and closes. Once power is cut, it opens again. For it to act as you are describing, it is stuck most of or all of the way closed even with power off to the valve.

Yes, all the 3-way valve solenoids I have touched were NO (normally open). When power is applied it will snap shut.