Lever pin diameter ~5 mm.

peacecup wrote:
Is this correct? This would seem to put a 43-mm flow over a 58-mm puck - is this not a recipe for uneven extraction? The PV piston and PF are of equal 45-mm diameter. I haven't seen any hint of side-channeling since about the first week of operation.

The small piston with larger basket would not necessarily cause uneven extraction. The gicleur and dispersion screen design could easily compensate.

peacecup wrote:The PV lever is 24 cm long from the piston cotter to the tip of the plastic handle. The lever appears to be ~1.4 cm diameter (about the same as the Achille). The two pins are ~1.6 cm apart, giving a rather high work-arm ratio? This would suggest a strong spring needs to be compressed? That, plus the narrow-diameter group gives a relatively high pressure?

The closer the pins are to each other, the greater the mechanical advantage. It's not unreasonable to surmise from the fact that the PV pins are only 16mm apart that there's a hefty spring inside. That is probably the case, though it's not necessarily the case. The lever dimensions would make the spring easier to compress, whatever size it was.

Yes, if the force remains constant, the pressure increases as you change the area to the which the force is applied. Larger area, lower pressure; smaller area, higher pressure.

Regards
Timo

Hold up folks, you only have half of the information. I am working on the rest. Forget everything you know about how a lever machine operates. The piston does NOT push water into the shower screen, it pushes COLD water into the HX, then from the HX into the lower group, out a dispersion block and out the shower screen.

Hold your horses. I am working on a very long and detailed post with lots of photos that I hope will explain how this nifty thing works.

Heat exchanger lever operation

The Achille has a very innovative system for pumping water through the group. I will try my best to explain how it works. Let me start by saying you need to forget how most piston-driven lever espresso machines operate. Clear your mind, this is not your normal lever espresso machine. In fact, it is more like a pump-driven heat exchanger espresso machine, but instead of an electric pump, you are using a hand water pump.

The Achille works with a pressure and vacuum action. The key is in the piston design. The group piston contains a hollow bolt and a one-way ball valve that allows water to flow from above the piston to below the piston on the upstroke, but closes under pressure of the down stroke.

A single up and down stroke

As the piston sits at the bottom rest position, the space above the piston in the piston chamber is full of water. Don't worry about how that water got there, just keep reading. As you raise the lever, a check valve on the heat exchanger water reservoir shuts so water can not be pumped back into the water reservoir. While the piston rises, the water that is above the piston flows through two holes just above the top of the piston:



The water continues through a hollow shaft down the center of the piston and out a large hex bolt with tiny holes drilled all over the face (think floor drain grating) on the bottom of the piston:



At the top of the lever stroke, the water that was above the piston is now below the piston. Now you start the down stroke. The one way valve in the piston closes. The water in the piston chamber is now pushed out through a tube in the bottom of the piston chamber and into the heat exchanger in the top of the boiler. It circulates through the heat exchanger coils and back out through a lower tube and into the lower group assembly. The water moves through the lower assembly and into the group chamber, then down through the dispersion block and out of the shower screen.

The diagram below shows the flow from start to finish:


Water flow to group exit


Water exit hole to dispersion block


Shower screen and dispersion block

During this down stroke, the space above the piston is drawing a vacuum because the one way valve in the piston is closed. Now the check valve in the heat exchanger reservoir tube that prevented water from flowing into the heat exchanger reservoir during the upstroke opens under the vacuum. The vacuum now sucks water from the heat exchanger reservoir back into the space above the piston. Remember the 'Don't worry about how that water got there' sentence at the beginning? This is how that water got above the piston.

In a nutshell: You raise the lever, the water above the piston moves to below the piston. You push the lever down. The water that is now below the piston is pushed out, passing through the HX and then into the water dispersion block. At the same time, the vacuum above the piston pulls water from the heat exchanger reservoir to fill the void above the piston.

A real stroke of genius

The piston is never in hot water. It is pumping from the cold side of the tank, just like an electric pump. Because the piston is isolated from the heat of the group, the seals will last for years. The piston is not exposed to coffee oils because the brew chamber is completely separate of the group piston. So there is never any need to remove the piston for cleaning. You just clean the dispersion block and shower screen just like any other pump operated machine.

After you pull a shot, don't forget to dump the puck, or it may be stuck to the shower screen an hour later.

Ah-ha, a wolf in sheeps clothing!

Thanks for the description, finally that parts diagram makes sense!

In Jim's Semiautomatica review he mentions the theory that it is the straight water path through the dispersion block that is responsible for lever machines distinctive shots, is the Achille dispersion block similar in design to the Elektra?

Henry

I cannot say. Jim will have to chime in on the Elektra comparison. The water path is most definitely straight down.

The dispersion block is aluminum on the Achille. I would much rather have stainless steel for ease of cleaning, but it still pulls a darn good shot.

Wow. That's such a brilliant design.

cannonfodder wrote:I cannot say. Jim will have to chime in on the Elektra comparison. The water path is most definitely straight down.

The dispersion block is aluminum on the Achille. I would much rather have stainless steel for ease of cleaning, but it still pulls a darn good shot.

From the picture, the water path to the dispersion block is very off-center; but it's hard to tell how well the block straightens and evens things out. The issue would be somewhat moot on a machine like this if it had a bottomless, since one can start with gentle pressure on the lever until the basket bottom shows an even black, and only then punch it to get the right flow.

I was referring to the physical water direction not the location in relation to the center of the block. Like an E61 whose water path is a 45 degree angle into the dispersion disk.

From the parts diagram, the Elektra has two dispersion blocks to better distribute the flow. But unlike the Elektra, I doubt a person will be able to generate the same instant 13bar pressure the Elektra's pump can ramp up to.

I never made a lever pull with the shower screen off to watch the flow out of the block. Sounds like a good reason to make another video.