shadowfax wrote:I think the material in that picture is ruby, like the stuff they cut high-precision gicleurs out of. I'm curious how elastomeric it is, but certainly it's supposed to seal. Most of the cores on the 3-way valves I have seen (including my Elektra and GS3) are viton, which is definitely elastomeric.

O.K., maybe like the green stuff here? (the viton I've seen was black)...

-Ed

Thinking back on that picture with the green stuff... if I remember right, the green showing is where the black seal had worn thru. -Ed

Huh, I always thought the dark color was green Viton stained with coffee oils, etc... I have a brand new, spare plunger for my GS3's 3-way solenoid, and it's green all over like the center of the plunger on the left in your photo:



The one that's currently in my machine (and has been since I got it in 2009) is discolored around the sides like the one in your photo, except not quite as darkly. I don't know much about Viton, though. From what I understand it's maybe a recent development that it's green and it used to be black, and maybe sometimes still is? I guess I originally got the notion that it's green because of the green Viton gasket on my Elektra's group bell; maybe this green rubber-like elastomer is something wholly other... who knows.

erics wrote:The pressure from the brew boiler (~12 bar - expansion issues) acts on the solenoid piston via a ~ 1.00 mm hole. The Linea's "hole" may/may not be 1.00 mm, but close enough

12 bar = ~174 pounds per square inch
1.00 mm diameter = ~ 0.00122 square inches
Force on piston = ~0.21 lbs = ~ 3.4 ounces

When the valve assembly is screwed in place, the spring gets compressed such that its opposing force is greater than 3.4 ounces.

Thank you so much! This is like Eureka to me!

By using this calculation, does that mean when we use a 58mm basket to make coffee ( provided that the pressure is 9bar), the coffee bed actually has 534lb of force on it and 446lb on the ones with 53mm basket in diameter? If this is right, then it shows the force on the 58mm basket is greater than the one on the 53mm basket even they both get 9bar, and is this one of the factors that makes they have a different taste in cup?

And I got another question. If the pump always provides pressure at 9bar, why do I see the gauge reads at 4bar when the water was filled into steam boiler? I can imagine when the steam boiler is full, the gauge will read at 9bar, but why doesn't it when filling? If the pressure is 4bar during filling, obviously the bypass valve isn't open. My water line pressure is somewhere around 4bar already, so does it mean the pump isn't adding up any pressure (or maybe a little) during filling?

I am sorry for all these questions, but it just bothers me if I don't figure them out.
Thanks!

MarcoChao wrote:By using this calculation, does that mean when we use a 58mm basket to make coffee ( provided that the pressure is 9bar), the coffee bed actually has 534lb of force on it and 446lb on the ones with 53mm basket in diameter? If this is right, then it shows the force on the 58mm basket is greater than the one on the 53mm basket even they both get 9bar, and is this one of the factors that makes they have a different taste in cup?

Yes, that sounds about right. And that would be the reason why the Aeropress can't make real espresso... unless you have an 800 lb press.

MarcoChao wrote:If the pump always provides pressure at 9bar, why do I see the gauge reads at 4bar when the water was filled into steam boiler? I can imagine when the steam boiler is full, the gauge will read at 9bar, but why doesn't it when filling? If the pressure is 4bar during filling, obviously the bypass valve isn't open. My water line pressure is somewhere around 4bar already, so does it mean the pump isn't adding up any pressure (or maybe a little) during filling?

It's about pressure-at-flow, I believe. A pump that delivers 9 bars at 60-90 ml/min (which is in the ballpark of what you get when you're brewing espresso will not necessarily deliver that same pressure when it's delivering a very high flow rate. The less the flow restriction, in general, the lower the output pressure and the higher the flow rate. A typical espresso machine rotary pump really ought to give you a pretty high pressure (say, 7-8 bars) when filling the steam boiler. a vibratory pump will likely deliver much lower pressure during that application. What's your machine again?

The pressure gauge indicates a pressure differential, between the piping and atmospheric pressure.

Think of it as a big guy pushing hard against you while you are on ice. Even if he push really hard, you won't feel much pressure. Then put yourself against a wall and have the same big guy to push. Then you feel pressure.

So... for the gauge to indicate pressure, you need to push against outgoing water (coffee bed, inside steam boiler pressure, etc. Otherwise, with water free flowing, the gauge will indicate near zero pressure, depending on where the pressure gauge is plumbed-in along the water path /pressure gradient (closer to pump: higher pressure; closer to outside air: lower pressure).

shadowfax wrote:I think the material in that picture is ruby, ...

(2nd writing of this... first one disappeared when I hit "submit"... hope it doesn't show up later.)
I have no skills in identifying materials by color. But I looked in the parts drawer and found the plungers from my two-plunger photo. As you suggested, the red stuff is very hard, and may actually be ruby. I find this an interesting choice for a seal against metal.
I poked at the black-and-green-ended plunger, and both the black stuff and green stuff are pliable. With no new specimen to compare to, I can't tell if the green stuff was once covered by black stuff, or if the seal was always made by the green stuff. It came from a Parker valve.

While we're on the topic, and before I lose these pictures, I'm inserting some shots of Parker and Lucifer 3-way valves, just one model from each. (I don't know about Lucifer, but Parker makes a zillion different valves. These are what I found at an espresso supplier). Parker (used) is always on the left, Lucifer (new) is always on the right. The colors of the plunger seals may or may not be factory originals.



I shot these pics during an unplanned exercise where I learned that you can put a Lucifer coil on a Parker valve, but you can't put a Parker coil on a Lucifer valve. Besides this, and the length, they appear to be interchangeable, although individual parts are not interchangeable between them.
-Ed

shadowfax wrote:Yes, that sounds about right. And that would be the reason why the Aeropress can't make real espresso... unless you have an 800 lb press.

Well, I have been hitting the gym a lot recently.

The fact that ~500lbs of force is applied to the puck also reinforces why even distribution is so important.

shadowfax wrote:It's about pressure-at-flow, I believe. A pump that delivers 9 bars at 60-90 ml/min (which is in the ballpark of what you get when you're brewing espresso will not necessarily deliver that same pressure when it's delivering a very high flow rate.

I don't have experience with rotary pumps, but Ulka vibratory pumps definitely follow a flow-pressure curve. This chart is straight from their website. The E5 pump is very common in espresso machines.

(Hopefully I'm not confusing this thread too much by continuing two separate discussions!)

shadowfax wrote:Huh, I always thought the dark color was green Viton stained with coffee oils, etc...

I have no evidence to contradict your statement. In fact, after scraping the black stuff with a utility razor, I got green (in the slot above center):

-Ed