I have a Londinium L1 V1. I have recently become interested in "turbo shots". Is there a way to do such a thing on my machine? Is the only option for lowering extraction pressure to "retard" the spring release by hand? Any other ideas?

with what ultimate goal?

After you release the lever holding it back by hand is pretty much your only option to slow the shot down, but it menas you're lowering the pressure.

Mark_Israel wrote:I have a Londinium L1 V1. I have recently become interested in "turbo shots". Is there a way to do such a thing on my machine? Is the only option for lowering extraction pressure to "retard" the spring release by hand? Any other ideas?

I've tried it on my L1 with good results.
Without a pressure profiling kit, when manipulating the lever, it's hard to know if your hitting 5 bar or maybe 7 bar...

I've had a few good results assisting the lever but also some inconsistency. I actually prefer letting the spring do the work and relying on grind and dose to hopefully hit the targeted pressure (6 bar or so).

My guess is that with such a looser grind, the puck isn't able to provide enough resistance to hit the full 8 bar of the Londinium spring. My guess, without a PPK to confirm is that when I nail the dose and grind right, peak pressure is actually closer to 6-7 bar.

I usually do 15g in / 45g+ out.

BTW, I've pulled super juicy turbo shots on my LP professional with a PPK. 12g in / 36-40g out at 6 bar.
It's been my go to light roast recipe these days.


Cheers!

Marcelnl wrote:with what ultimate goal?

After you release the lever holding it back by hand is pretty much your only option to slow the shot down, but it menas you're lowering the pressure.

The original study and recipe for Turbo shots suggests a 6 bar extraction.

I don't necessarily lower the extraction pressure to make a fast shot. I let my shots run quickly at the 8 bar with a decline when I did it on the spring. With these style shots, the fundamental principle is all the same: a faster flow rate is more even. Downdosing, reduced extraction pressure and long ratios are secondary to that beforementioned principle. Just grind coarser and do the same thing you always do, and let the shot run fast and maybe pull a little longer if the shorter shots don't taste balanced.

side note: spring levers are stores of energy and they are the closest we have to pure pressure profilers. As in, even at high flow rates, assuming that the spring catches at the same height and preinfusion is done correctly, they will hit the full 8 bars. Springs can provide extremely high flow in order to hit extraction pressure, which is why they are disasters when you let go without a portafilter. I have pulled high pressure shots that flowed in 10 seconds on my spring lever before. Pumps have limited power output thus may not reach a given extraction pressure at a given flow rate but springs do not share that limitation.

LObin wrote:The original study and recipe for Turbo shots suggests a 6 bar extraction.

TA!

so adjusting pre infusion appears to be the solution.

On a more recent Londinium that has variable PI, it's a great avenue indeed.

On a first gen L1, preinfusion is limited to boiler pressure...

Still I doubt a 15-20s fast flow pull reaches the full 8 bar spring pressure. So my guess is there's no need to hold the lever when pulling Turbo shots on a dipper style spring lever.

There are two opposing pressure gradients in espresso. One is from the top to the bottom of the puck and that's the one that the spring effects. A turboshot hits 8 bars because of the spring force, but the other pressure gradient is lower because the puck offers less resistance and that's why it goes faster. With that coarser grind, as the spring potential decreases, less energy goes towards increasing the pressure of the system so the kinetic energy increases instead.

If you apply a force over an area, the pressure will be the force/area. If the spring catches at the right length to produce 8 bars normally, then the force will not be any different on the top of the puck (if we assume water is incompressible) because the force of a stretched spring is proportional to the length it is displaced. Will it flow much faster? Yes. But you're hitting 8 bars