Dual Screen Tweaking

[chas]

If you look at each of the two shower screens, the hole pattern looks the same and very regular on both. However, if you take the two clean screens with the bolt through the hole, stand under a bright light, hold them over your head, and slowly rotate the smaller screen you will see something interesting.

The light pattern you see changes drastically. At one extreme I see light coming through four large equally spaced circular areas that extend the radius of the screen with no light coming through anywhere else. At the other extreme, I see a evenly distributed pattern of tiny holes. Consequently, might the relationship of these two screens to each other make enough of a difference in water flow to impact either the quality of the shot or at least the likelihood of channeling?

I am working on some experiments with this. The jury is still out. However, I encourage others to play with this as well and let me know what they think.

[Niko]

I never thought of that, wow.
This experiment is very interesting.
One way to show us something would be a pressure gauge at the PF to notice any changes in pressure.
Do you still have yours, Chas? I can't remember if it was you who broke it
Someone mentioned they dropped it a while back and destroyed it.

Anyhoo, I'm still waiting for my Scace II Device with the pressure gauge at the PF (@ the end of the handle).

[Weska]

Intriguing observation, chas. And one I've never encountered anywhere else.

Thinking about it now that you have mentioned it, I'm going to guess that the effect, if any, is indirect. The more the holes are aligned, the more quickly dwell time passes and the extraction begins in earnest. The more the holes are not in line with each other, the longer it takes to fill the headroom above the grinds.

In other words, maybe alignment of those two screens shortens the "natural" pre-infusion.

[chas]

I found that in trying to test the effect, aligning the screens, then trying to get them inserted and screwed down while holding them in alignment is very difficult. It is easier to insert the screens and then screw in the bolt until it is almost tight. Then you can use the tip of a clean rag or sponge to rotate the bottom screen, then hold it in place with that rag or sponge while tightening the bolt.

By doing this you can rotate the screen perhaps 1/8 or a turn each time, then hit the 2 cup button and observe the resulting water pattern each time.

[bbqnut]

Once the "best" pattern is discovered, I think the answer is one screen. Then the result is always the same.

[Niko]

We should capture images of the patterns to compare...

And what I meant earlier about a pressure gauge, maybe a super accurate one that measures in PSI rather than Bars?
Maybe a slight turn of the screens and one can see a slight pressure difference. Maybe ounces per square inch

[EricC]

I don't think that there would be any change in pressure at all.

The only thing that would change would be, as Weska mentioned, a change in the "natural" pre-infusion time. Also less chance of channelling due to less of a direct path, with the holes not aligned.

If the holes in the two screens were aligned then the water would have a path / paths of least resistance, and would choose this / these over all others.

[wgaggl]

Chas, you raise a very interesting point, and I was wondering about that before but never started looking at it systematically. The flow pattern from the group without PF looks somewhat different depending on the orientation of the screens anyways.

I think there might be some difference to it. Not from a point of pressure or total flow rate, but regarding flow pattern and water turbulences. These turbulences could make a difference for sensitivity to channeling with existing imperfections to the puck surface.

So most likely you will need many samples, and please make note about any occurrence of channeling (using the naked PF) or shortening of shot time before blonding occurs.

This might be interesting,

Wolfgang

[Niko]

I was thinking about this during my latest Cafiza Night. The pattern was definitely different when the screens were rotated in different directions, it must affect channeling in some way (like Wolfgang mentioned) but I quickly finished my backflushing and cleaning to resume the shot-pulling.
I'll look into this next time, if I find some configuration that works better - the screens will get notched or marked in a way to repeat this over again.

Has anyone else toyed with this yet?

[chas]

I haven't reached any conclusions yet, but I do have a recommendation to those that want to try. When you hold the pair of screens up to the light and rotate them unto a configuration you want to test, put a line across the edges with a Sharpie. Then you can hold the screens in your desired alignment as you tighten the screw/bolt. Otherwise, the bottom screen will rotate relative to the top screen without you realizing if it twisted or how much.

[Niko]

I like the kaleidoscope and sharpie idea.

[admin]

As I noted in my previous post, I haven't decided how much difference the screen orientation makes or how much difference there is between various orientations. As Wolfgang noted it seems reasonable that there would be differences in the water flow.

Given that and given that I would like to eliminate variables, I rotate my screens so that I see that maximum number of the smallest holes possible. This may not yet turn out to be optimum orientation but having the screens in the same orientation all the time has to introduce some additional level of consistency.

[spaz2]

I too have been rotating the screens for a while now as a result of having some channeling right after a weekly cleaning. After reinserting the screens I punch the button and look at the flow pattern coming out of screens and then loosen the bolt holding the screens and give the lower screen a little turn if I see the flow is primarily in the middle.
Also I have a very thin washer between my flipped screens so they don't completely crush together when the bolt is tightened and I only snug the bolt lightly. I agree a minute spent adjusting the screens does give a shower head looking dispersion of the water and seems to help avoid center channeling.

Thanks to Chas for the original the tip about flipping the screens. Making that change and grinding down the bolt head to half its original thickness clearly allow more coffee and reduces center channeling. (if you grind down the bolt head don't forget to grind the tool face too or it won't tighten the bolt)

[chas]

Ah, you're flipping the screens. I concur that you need a washer between the two in that configuration. I ruined a set of screens by not doing that. Without a washer, the large screen bent so that there was a gap between the screen and the diffuser - not good.

In the normal configuration, the smaller screen has an indentation which eliminates the need for a washer.

[BobUSN]

How tight are you making your screen bolt on the newer screen configuration? Cinch it up snug or leave some slack?

(Aia if I missed other posts on this.)

Thanks!

[Endo]

I don't know of ay new screens .

But if you're wondering about the bolt torque, I suggest simply holding the tool with the thumb and forefinger only. Put your finger and thumb close to the shaft of the tool when doing the final tightening. This will limit the torque you can apply to approximately the correct amount.

Is it just me....or do that sound obscene?

[BobUSN]

Thanks Endo. "Newer screen configuration" meaning newer than the configuration that was shipping with the original Vivaldi.

viewtopic.php?f=26&t=15&p=42&hilit=tigh ... n+bolt#p42

Yes, Endo, you make me feel so...dirty.

;~)