another_jim wrote:The Ulka pump is just 55 watts or so, so a dimmer for the pump alone does not to be expensive. Doing the lower pressure preinfusion "by ear" is somewhat hit or miss. The alternative is to cut the dose without changing the grind, so the espresso starts flowing at lower pressure. Once you see flow, lift the lever slighty (or move it to the right) to cut the pump and finish the preinfusion by holding it there for a few seconds

I cut the pump once I see coffee coming out from the basket. Even I hold the lever there, the flow has started nonetheless. So the preinfusion I have, if I can call it a preinfusion, is one with the shot already started.

You'll probably get used to anticipating the flow. But the flow you get without pump or lever is created by the expanding air pocket in the cylinder -- I'd be surprised if it comes to more than 5 grams before it peters out, although I've never measured it.

On a more general note: There never was much evidence on conventional pump or lever machines that the length of the preinfusion is a factor in taste. Our experience on the Strega suggests that the pressure at which flow occurs is a factor. However, I really don't have enough experience to make any hard statements. I may go with John's dimmer mod just so I can run do a long run test. I just need to figure out how to do it blind (In ear monitors playing heavy metal? USB dimmer controlled by a random number generator? The mind boggles)

New machine, with less than 20 or 30 shots. 1st shot this morning, using the same grind and dose that seemed to work before. Drop the lever and enaged the pump and hit the clock. And the pump never shut off, just kept going and going, no flow, and the expansion relief valve(over pressure valve?) tripped and started flowing into the tray after 10-15 seconds. After bout a minute I released the lever, the pump shut off and I got a slow choker that took 2 minutes or more to extract.

Never experienced this pump behavior before with other "chokers" and am curious if that is a normal sequence of events or does the pump or ERV need adjusting? Shouldn't the pump pressurize the portafilter up to "x" lbs and then shut off, especially with a choker and no flow bleeding off pressure.

Anyway, backed off the grind a little and got a more normal sequence with the pump shutting down around 10 seconds into the shot, which was also about the same time the flow began.

Any ideas or is that relatively normal with "some" chokers?

Ok got it, makes sense. Then what happened that time, causing the ERV to trip and water continue to run freely into the tray until I shut the pump off by lifting the lever?

Vibe pumps develop about 18 bars pressure; whereas the OPVs are typically set in the factory at around 11 bar (give or take a bar). So one would expect it to begin leaking as the pressure rises in the cylinder and hits the OPV's setting level. This is often the case; but not always.

The arrangement of the OPV in the Strega is unusual in that it is integrated with a backflow check valve. I think this makes it a little sticky or slow, so that it sometime takes a few seconds to open when the pressure rises above its set point. I have noticed mine on occasion staying dry as the cylinder fills and the pump is running, but dripping as the lever is operating. Since the pump pressure maxes higher than the spring; this means there is some kind of time delay.

This may be what you observed

I'll keep an eye on it.

Thanks Jim.

another_jim wrote:You'll probably get used to anticipating the flow. But the flow you get without pump or lever is created by the expanding air pocket in the cylinder -- I'd be surprised if it comes to more than 5 grams before it peters out, although I've never measured it.

measured today. If I hold the lever, about 5-6 grams comes out before the flow stops.

JohnB. wrote:I'm having Dave make up a set of wooden (Macassar Ebony) handles/knobs for my Strega so I needed to remove the various pieces & determine the correct thread sizes.

No threadlocker on the steam/hot water knob threads so they unscrew easily. If yours are on tight grab the exposed end of the shaft with a pair of needle nose pliers to keep it from turning. The knobs screw onto an 8mm X 1.25 threaded shaft that extends 20mm into the knob.

John:

It appears that the Londnium folks (Francino) use thread locker on the water/steam toggles

I have tried everything except take the valve off the machine and dismantle it from there!

Suggestions?

And no, I have no intention of hijacking this Thread. Please PM me.

Stephen:

You can heat them up with a heat gun, it will soften the thread locker, and you'll be able to get them off. Just keep in mind, you'll have to get them pretty hot.

I've also put portafilter handles in pots of boiling water for the same purpose, but you can't exactly do that with your steam and hot water valve handles


- Rick