Has anyone ever PID'd a lever machine? - Page 3

A haven dedicated to manual espresso machine aficionados.
User avatar
HB
Admin

#21: Post by HB »

hbuchtel wrote:Take a lever machine that depends on boiler pressure to force the water to the group head (such as Pavoni), and two different situations,

1. a full boiler 2. a boiler only 1/3, 1/4th full of water. Assume everything else is the same.

Ok, so say both have been boiling long enough to provide the necessary pressure to get the water up the the group head. Now, if you could measure the temperature of the water in the boiler, would they both be at the same temperature? Would the boiler with less water be at a lower temp then the full boiler (or the reverse?)
It isn't the quantity of water that affects the boiling point (and thus the boiler's temperature), but the pressure within the containing vessel. From the Wikipedia definition of boiling point:
The boiling point corresponds to the temperature at which the vapor pressure of the substance equals the ambient pressure. Thus the boiling point is dependent on the pressure. Usually, boiling points are published with respect to standard pressure (101.325 kilopascals or 1 atm). At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased ambient pressure up to the critical point, where the gas and liquid properties become identical.
As a practical matter, the group will heat differently depending on the boiler's water level. Not because the temperature of the boiler is different - it remains the same at the same pressure whether it is 1/4 full, 1/2 full, or 3/4 full - but because of the thermal conductivity difference between water and water vapor. An easy analogy helps explain this difference: You're in a steam room and the temperature is 140 degrees Fahrenheit. Tolerably hot for a few minutes. Now you're immersed in water at 140 degrees Fahrenheit. Your life is in grave danger.

I'll leave it to the physics majors to explain the details.
Dan Kehn

User avatar
hbuchtel

#22: Post by hbuchtel »

Hey Dan, thanks for your reply,

What I'm trying to get at (and cannot explain very clearly) is not the boiling point or how much heat gets conducted from the water, but rather . . . is the pressure in the boiler only related to the temperature of the water in the boiler? Does it also depend on the ratio of water to . . . (air, gas, steam, empty space . . . how to describe it?) empty space in the boiler?

What I'm hoping (damn the physics!) is that changing the ratio of water to space-without-water will also change the temperature at which you have enough pressure to push the water to the group head. . .

But perhaps this is not possible . . . no laughing please!

-Henry

User avatar
HB
Admin

#23: Post by HB »

hbuchtel wrote:is the pressure in the boiler only related to the temperature of the water in the boiler? Does it also depend on the ratio of water to . . . (air, gas, steam, empty space . . . how to describe it?) empty space in the boiler?
Yes. No. If the water is below its boiling point, there's no pressure, and a pump must be used to push the water to the grouphead.
Dan Kehn

User avatar
hbuchtel

#24: Post by hbuchtel »

Got it.

Temperature and pressure (as talked about in many other posts :oops: ) are directly related. The ratio of water to air will only effect how much heat is conducted to other parts of the machine, it will not effect the temp of the water in the boiler.

Well that's good to know! Now I can move on to less useless trains of thought . . .

-Henry

lino

#25: Post by lino »

hbuchtel wrote: 1. a full boiler 2. a boiler only 1/3, 1/4th full of water. Assume everything else is the same.

Ok, so say both have been boiling long enough to provide the necessary pressure to get the water up the the group head. Now, if you could measure the temperature of the water in the boiler, would they both be at the same temperature? Would the boiler with less water be at a lower temp then the full boiler (or the reverse?)
Let me clarify a little: the boiler in a MicroCasa (and probably the Pavoni) cannot be completely filled since there is always a bubble at the top...

They are saturated steam systems and as such temperature and pressure are directly related to each other. How full the tank is doesn't matter. You can do a search for "saturated steam table" and you'll find tools to let you enter the pressure and get temp, or vice versa.

So to answer your question directly, if they are at the same temp, they are at the same pressure.

ciao

lino

User avatar
another_jim
Team HB

#26: Post by another_jim »

lino wrote:Hey Jim,

dunno how I missed that post for 3 whole days... Sorry.

I just lift the lever manually, assisting the spring.

One hand on the drip tray holding the machine down, one hand on the lever pushing it back up. One eye on the pressure gauge trying to keep it near 9 bar.

The lever is actuated with a direct mechanical linkage (crank arm type) so you can back drive it.

ciao

lino
Cool! I'll have to try it -- how to turn a spring lever into a direct lever.

RCMann

#27: Post by RCMann »

Just joined the group so I'm a bit late to this one, but from what I'm reading here, is it the consensus (or the fact) that a Pavoni can't be PIDd?

A previous poster mentioned wrapping copper tubing around the grouphead-how about adding a small pump to circulate cooling fluid through the tubing, maybe adding some extra lengths of tubing somewhere around the machine to act as a radiator, then putting a PID in the tubing to start/stop the pump to maintain a consistent grouphead temp? Can a PID do that?

Sounds pretty elaborate, but may be possible if a small enough pump could be located. Rube Goldberg?
Matt Chester fixed gear

User avatar
mbach

#28: Post by mbach »

What about placing between the grouphead and the machine (where the head gasket is located) another heatsink/radiator. I'm thinking like the vanes on the outside of my ac compressor. Just 1/2 inch or so (can't be too think or machine balance would really suffer) of these between the machine and the group. Only real plumbing would be lengthening the water inlet tube. Right? Could be a quick and easy, maybe even attractive, kit.
matthew

User avatar
another_jim
Team HB

#29: Post by another_jim »

another_jim wrote:
Cool! I'll have to try it -- how to turn a spring lever into a direct lever.
So, I've been playing with the manually assisted spring lever (unfortunately with no pressure gauge to guide me), making shots for about 12 coffees I'm reviewing for coffeecuppers.

Initially I assisted all the way, using roughly half the force I use to pull down (i.e. 6 bar * 1.5). The crema was full guiness effect, and the mouthfeel much improved. However, the shots were bitter/muddy. So I went to providing an initial assist, then easing up at the halfway point. This gets the best of both worlds. Shots where the grind was perfect (tougher with this method and much tougher than on the Tea) had that elusive "mousse" mouthfeel I've sometimes had from very good LM shots (wait for a long line at Intelligentsia when Amber is pulling shots). In any case, I'm a convert. BTW, the technique will also work for elektras.

Haven't done that many shots yet, about 25 or so, but based on them, I'd say there's some serious mojo in the declining pressure profile. Basically, towards the end of the shot, when the flow lightens and accelerates, crema forms at very low pressures (this is how the trick mochapots do it), but is quite unstable. The stable crema forms early, and requires high pressure. Even in pump machines, the first few seconds of flow is liquid, not crema. Oddly, with the long, no pressure preinfusion of a lever, and the pressure assist, I'm getting crema right off the get go.

There's obviously some gold to be had in pressure profiling, but experiments should include no pressure preinfuse + sudden ramp up profiles as well. It may be this start, rather than the finish, that distinguishes some star "mouthfeel" machines. I think my variac experiments on the Tea were compromised by the slow E61 pressure ramp up being unmodifiable. This ramp up does create heavy body and forgiving consistently well flavored shots, but may make the "mousse" mouthfeel effect impossible.

User avatar
AndyS

#30: Post by AndyS »

another_jim wrote:There's obviously some gold to be had in pressure profiling, but experiments should include no pressure preinfuse + sudden ramp up profiles as well.
Cool, Jim, I can't wait to experiment with this.
-AndyS
VST refractometer/filter basket beta tester, no financial interest in the company