timo888 wrote:The group cap shown earlier is a retro 'low-tech' design that uses a simple pliable washer as the one-way valve. Here is a more high-tech version of the group cap which has been tapped with holes into which modern one-way check valves (not shown) would be fitted. We want excellent water flow from the piston chamber down to the dispersion screen so there are multiple check valves to increase the total effective orifice diameter.

image: http://www.aimsdata.com/tim/espresso/beast/BeastGroupCapHighTech444.jpg

Tim,
I have to disagree with you on this one. Only because of my recent diassembly of my Silvia ( now sold---alsa...) After preping my Rancilio Sivia for sale, I took the dispersion screen off etc. The area under the mesh dispersion screen hasis an inverted brass mushroom inserted into the main water orfice ( or golf ball marker looking insert that acts to keep the water from being directed straight into the screen and into the puck surface. This mushroom has grooves eminating from the center and radiating out to the edges. Maybe 6 or 8 grooves.
See if you can get a look at this arrangement because the washer would act as the same type of diverter and move the water out to the edges . Here it would flow back to the area under the washer and fill the entire void above the screen. Giving an even flow.
I most likely have described this poorly , but see if a search of a site like wholelattelove on cleaning tips etc shows this. It may have an impact on your design ideas and then again....maybe not so much:oops:

One is just much more clean in design, less servicable parts. In an area as prone to build up etc , the washer would be very self-cleaning. That my vote!!

timo888 and mogogear,

I take the liberty to propose multiple marriage

One could use:

The "one-way valve" of the All-Clad Presso interesting
The type of heating used on the Gaggia domestic pump machines
Open boiler type used on Peppina and others
Piston/cylinder dimensions from a commersial lever machine
Shower screen from the above commersial lever machine
PF gasket, PF and PF holder from a pea-valve Gaggia domestic machine


....B....................Rod...................B
....B....................Rod...................B
....B....................Rod...................B
....B....................Rod...................B
....B....................Rod...................B
....B....................Rod...................B
..HB....................Rod...................BH
..HB....................Rod...................BH
..HB....................Rod...................BH
..HB....................Rod...................BH
..HB....................Rod...................BH
..HBBBB..............Rod..............BBBBH
..HBBBB..............Rod..............BBBBH
..HBBBB..............Rod..............BBBBH
..HBBBB..............Rod..............BBBBH
..HBBBB..............Rod..............BBBBH
BBBBBB_P__i__s__t__o__n_BBBBBB
BBBBBB_P__i__s__t__o__n_BBBBBB
BBBBBB_P__i__s__t__o__n_BBBBBB
BBBBBB__Shower.. screen__BBBBBB
GGGGG....................................GGGGG


B= Body (outer diameter 80mm at the heater)
H= Heater (used in plastic moulding machines)
G= Gaggia PF holder

The PF holder from the Gaggia needs to be modified a little (remove the center). Then it bolts directly to the "body".

As the piston diamater commes from a commersial lever machine the spring data can be copied.

Indications show that constant flow gives a good result which means the piston could be driven by a screw at constant speed (one stroke/25 sec.). That way somekind of preinfusion would take place as the grounds I believe create less resitance when dry.

The design ended up this way as I believed it makes it easy to make with limited resources (all parts can be made with a lathe and a drilling machine) and easy to clean. Here I stopped as I can't find an easy way to avoid ruler flat temperature.

Edit: I removed an O-ring between the Body and the PF-holder as it is not needed.

mogogear wrote:Tim,
... insert that acts to keep the water from being directed straight into the screen and into the puck surface...
One is just much more clean in design, less servicable parts. In an area as prone to build up etc , the washer would be very self-cleaning. That my vote!!

The group cap is a self-contained assembly that will screw into place, and so we can have it both ways retro-tech washer or today's check valves. We could sell this machine as a build-it-yourself kit like a barebones PC, offering, for example, different wattages on the heating elements. Marketing could steal some ideas from PC makers. 'Powerful twin 700-Watt heating elements, one for brew water, one for steam.'

I agree, we'd want to have an even distribution of water to the dispersion screen. The array of valves and a properly designed dispersion screen should address your valid concerns about not wanting to disturb the puck surface. The circular array of valves should distribute the water nicely to the dispersion screen. My hunch is that above the 'golfball' in the Silvia there is not an array of egress ports but a single egress port from the pump, and hence the need to break up a stream of water.

As a point of comparison, in the Peppina, there's a canal leading from the piston cylinder to the group head. The canal has a diameter of ~5mm. The canal leads to two (2) small egress holes on the group above the dispersion screen which are 2mm diameter each. So the Peppina's dispersion screen is fed by an effective orifice diameter of only 4mm. The effective orifice diameter would need to be larger for a 58mm screen, but I feel confident that the circular array of check valves would provide ample egress for water from the piston chamber to the group without the kind of concentrated streaming that requires a pre-dispersion before the water hits the dispersion screen.

The centrally placed check valve might need to become a post for the piston head to abut against.

Regards
Timo

Mathias,

In the design I have in mind, the one-way valve assembly (I call it the 'group cap') is a threaded cylinder with a plate which contains the array of egress ports and the valve(s). The group cap connects the bottom of the piston cylinder to the top of the group cylinder, which protrudes into the boiler. The group-cap is a fairly extensible design and it could accommodate other kinds of one-way valves. It's not clear to me where the one-way valve fits in your diagram and I'm not familiar with the All-Clad one-way valve. Could you describe it?

I am certainly a proponent of simplicity. The group should be very simple. It needs a cylinder that projects up into the boiler, and collar to bolt it to the underside of the boiler, and a cylinder on the bottom into which the PF locks. The water will be at the correct temperature and so we don't need anything fancy in the group. No thermosyphons etc etc. I would like to be able to make use of readily available OEM portafilters.

Regards
Timo

Mathias again,
Please bring me up to speed on the Heating device you're talking about. I am not familiar with it. At first glance it strikes me as an unnecessary complication to have a heating device on the piston, but maybe I don't understand it?

In the design that has evolved so far, the piston is inside the boiler within a cylinder that extends from base of boiler (top of group) up to the lid of the boiler. The water in the boiler is heated by either an immersible element (like Peppina) or by an element that sits beneath the boiler (like Arrarex Caravel).

Regards
Timo

timo888 wrote:Mathias again,
Please bring me up to speed on the Heating device you're talking about. I am not familiar with it. At first glance it strikes me as an unnecessary complication to have a heating device on the piston, but maybe I don't understand it?

You can see one here http://makeashorterlink.com/?B2E91233D

The heater is not on the piston but on the outside of the boiler (B=Body). I tried to show the idea with the "drawing". The boiler and piston cylinder is made in one piece. The PF holder could be made within the piece as well bu to me it seemed a lot easier to take one from an old Gaggia, "cut" out the center and just bolt it to the "Body".

timo888 wrote:Mathias,

In the design I have in mind, the one-way valve assembly (I call it the 'group cap') is a threaded cylinder with a plate which contains the array of egress ports and the valve(s). The group cap connects the bottom of the piston cylinder to the top of the group cylinder, which protrudes into the boiler. The group-cap is a fairly extensible design and it could accommodate other kinds of one-way valves. It's not clear to me where the one-way valve fits in your diagram and I'm not familiar with the All-Clad one-way valve. Could you describe it?

I am certainly a proponent of simplicity. The group should be very simple. It needs a cylinder that projects up into the boiler, and collar to bolt it to the underside of the boiler, and a cylinder on the bottom into which the PF locks. The water will be at the correct temperature and so we don't need anything fancy in the group. No thermosyphons etc etc. I would like to be able to make use of readily available OEM portafilters.

Regards
Timo

The All-clad can be seen here http://www.home-barista.com/forum...-machine-t210.html

mathias wrote:You can see one here http://www.home-barista.com/forum...-machine-t210.html

The heater is not on the piston but on the outside of the boiler (B=Body). I tried to show the idea with the "drawing". The boiler and piston cylinder is made in one piece. The PF holder could be made within the piece as well bu to me it seemed a lot easier to take one from an old Gaggia, "cut" out the center and just bolt it to the "Body".

OK, I think I see what you mean. The piston is immersed in the boiler water? When the piston retracts, does it displace water? Where are the seals? Or is the piston in its own cylinder which is inside the cylindrical boiler?

One of the design goals is to have a minimum of 400ml of water at stable brew temperature. When the 500ml boiler is down to 100ml remaining, fresh (i.e. cold) water is pumped into it from the reservoir -- in the auto-fill model. There's a less expensive manual refill model. Everything is a-la-carte. Barebones Beast.

In the gravitational model I have in mind, the boiler water is immediately above the group. Straight down to the puck. One of the drawbacks of the band heating element you've suggested (at least with the specific band element at the link provided) is that with an 80mm maximum diameter one needs a fairly tall boiler to get 500ml of brew water, especially if the boiler houses a piston/piston rod and perhaps also a piston cylinder.

But if there are band elements of greater than 80mm diameter, that type of element would indeed present an alternative to the immersible element and the Arrarex-style element-below-boiler.

Cylinder's Volume = Pi * Radius squared * height (minus whatever volume is displaced by stuff inside the boiler, piston etc). We're talking 12-14cm or more in height, depending upon what's inside the boiler cylinder that takes up space. Not a tall boiler for a pressurized machine, but for a gravity-based design with the boiler directly above the group, too tall. Remember, it has a lever on top, so height and center of gravity are primary concerns.


It's positioned to be a home machine. I have been aiming for something with the MiniGaggia's form-factor. No too tall and imposing. A home machine with some wife-appeal. My wife thought the Rancilio Silvia was huge and institutional-looking, for example. We don't have the budget for focus groups, so she will have to suffice as Everywoman.

I have to leave for work but will check out the one-way valve of the All-Clad later today.

Regards
Timo

For the spring-style lever, the downstroke compresses the spring and causes the piston to retract. In the design I've set out here, piston would retract upwards. When the piston retracts, we want to prevent water traveling from the puck up into the piston chamber but allow water to flow into the piston chamber from the boiler. I think my group cap with one-way valve(s) between dispersion screen and piston addresses this issue better than the All-Clad piston's rolling gasket design would. Going to stick with the simple and extensible group-cap

Regards
Timo

timo888 wrote:
OK, I think I see what you mean. The piston is immersed in the boiler water? When the piston retracts, does it displace water? Where are the seals? Or is the piston in its own cylinder which is inside the cylindrical boiler?

Yes / very little (if retraction is slow enough) / one O-ring on the piston, see All-Clad (doesn't show on my drawing") / piston cylinder is below cylindrical boiler (same piece of metal though).

timo888 wrote:One of the design goals is to have a minimum of 400ml of water at stable brew temperature. When the 500ml boiler is down to 100ml remaining, fresh (i.e. cold) water is pumped into it from the reservoir -- in the auto-fill model. There's a less expensive manual refill model. Everything is a-la-carte. Barebones Beast.

My goal was 6-8 doubles (225-300 ml).Manual refill.

timo888 wrote:In the gravitational model I have in mind, the boiler water is immediately above the group. Straight down to the puck. One of the drawbacks of the band heating element you've suggested (at least with the specific band element at the link provided) is that with an 80mm maximum diameter one needs a fairly tall boiler to get 500ml of brew water, especially if the boiler houses a piston/piston rod and perhaps also a piston cylinder.

Same model. I've seen 100mm band heaters though I was going for the 80mm. 300 ml, inner diameter 70mm gives a length of 128 mm. With a 100 mm heater you could have 90 mm inside diameter. 500 ml would then give a length of 127 mm. The actual length need to compensate for the piston rod (and the spring if it is placed within the boiler)

timo888 wrote:Remember, it has a lever on top, so height and center of gravity are primary concerns.

With a 47 mm piston diameter ( http://makeashorterlink.com/?O56E4233D ) and 75 ml/pull the stroke would be 43,2 mm (the Gaggia doesn't make a double/pull) . My idea was to have the spring and lever mechanism behind the group. That way the lever axis could be at the base a la Peppina and allow for a longer lever. The total height would then be 220mm (appr.) + PF + cup height + drip tray. I think I ended up around 500 mm. 8,5 bar requires almost 1500N with a 47 mm piston. 150N pull force gives a 1:10 ratio. A 43mm piston stroke then requires a 430mm long lever.

timo888 wrote:It's positioned to be a home machine. I have been aiming for something with the MiniGaggia's form-factor. No too tall and imposing. A home machine with some wife-appeal. My wife thought the Rancilio Silvia was huge and institutional-looking, for example. We don't have the budget for focus groups, so she will have to suffice as Everywoman.

Women are powerful aren't they
Would this be a machine for the market? Mine was just intended for me, therefore a design that could be made with little shop capacity.