# Why does the brass dispersion plate have different dimensions??



## Michael87 (Sep 20, 2019)

I've just fitted the original spec alloy dispersion plate and found the four holes are bigger than the brass ones. Do we know why?

I understand brass has better thermal performance but I think the change in hole dimension has a big impact on shot flow. I've only tested it once but I think I prefer the taste of the original one?!

What's going on here!!


----------



## Deegee (Apr 5, 2020)

I seem to recall a post somewhere that was saying the slightly smaller holes in the brass plates were effectively "jetting" the water through the shower screen and possibly causing channelling, the OP had gone back to the original alloy plate and the issues had stopped. I'm not sure if that's the kind of thing you're experiencing, but it sounds plausible.

Edit, no answer as to the why, sloppy manufacture maybe?


----------



## Abcan (Jan 10, 2020)

Hi. I think this thread will help. I had the same problem as you and found I got far better results with the alloy plate.

https://www.coffeeforums.co.uk/topic/26713-brass-dispersion-plate-drilled-out/?tab=comments&do=embed&comment=725488&embedComment=725488&embedDo=findComment#comment-725488


----------



## mr-bean (Nov 26, 2018)

I fitted the brass one last year and changed it back to the original because of channeling. I got 2 distinct dimples every time, even after setting the OPV lower.

It seems I missed the post on drilling out the brass, might give it a try again.


----------



## Agentb (Feb 11, 2017)

I have noticed it helps (or worsens - lol) a bit if you rotate the screen IMS screen a few degrees - easiest to do by loosening the screen screw, rotate a couple of degrees and re-tighten.

If you do consider drilling more holes look at where the single inlet hole is above the block, and do not add a hole in line with that for obvious reasons.

If it bothered me more i'd drill two small 2mm holes as the 4 exiting holes are about that, rather than enlarge the existing holes.👍

edit: i found it's more a function of the IMS screen rather than the shower block - if that makes sense..

edit: looking at the photos in that thread - another thing which might be making a difference for me, i'm usually dosing 17g in a 18g basket so a little more headspace.


----------



## Skizz (Feb 10, 2020)

Thought I'd sorted my brass block issues (used with IMS screen) by enlarging the holes, adding two more in the middle and countersinking the outlets to reduce velocity. Problem-free for a couple of months until I descaled two days ago and now I'm getting a deep crater in line with the rearmost left hand hole and noticeable channelling. Rotating the screen makes no difference. No idea why the problem has come back (and worse than it was) but honestly cant think of anything else to try.

I think the broader issue is that the aftermarket brass and stainless blocks are designed for the commercial Gaggia machines rather than the Classic which, has a single, off-centre inlet point as opposed to centred or multiple inlets. This causes uneven pressure across the dispersion block, leading to the jetting/cratering issues we all know about. This is compounded by the IMS screen, which allows these jets to pass straight through without slowing. Have ordered an original pattern screen and hoping the fewer and smaller perforations will do the trick.

For reference, I'm dosing 18g into an 18g VST basket and running the machine at 9.5 bar static.


----------



## Rebel (Jan 14, 2020)

Are you getting channeling as viewed from the output of a bottomless portafilter? That's all that counts. Looking at the top surface of the puck tells you nothing since that's mostly affected by the suction of the solenoid kicking on.


----------



## Skizz (Feb 10, 2020)

Rebel said:


> Are you getting channeling as viewed from the output of a bottomless portafilter? That's all that counts. Looking at the top surface of the puck tells you nothing since that's mostly affected by the suction of the solenoid kicking on.


 From my own results, yes, severe channelling.


----------



## mr-bean (Nov 26, 2018)

Skizz said:


> For reference, I'm dosing 18g into an 18g VST basket and running the machine at 9.5 bar static.


 This is exactly the way I am set up and with the brass block I got channeling, with the genuine block I have a perfect puck, so it is the brass replacement that's not up to spec.


----------



## Bagpu55 (Dec 23, 2019)

Its such a shame we cant get an even pressure across the block, Im sure this would make a massive difference.


----------



## Agentb (Feb 11, 2017)

I did a quick check and i'm running at 9.5 bar so it's not that.

Just as matter of interest - what sort of shot times, i am using a 18 or 20g basket with17/19g typically i find for my taste shots around the 38-42s are fine (ratio is 2.5 to 2.6 ).

If the shots are faster the water has to flow faster.

The other thing i noticed on one of the photos of Skizz's pucks, it looks like the outside of the shower head / screen is touching the puck - which i don't normally see..

If i remember i'll take a photo or two tomorrow. 😺

edit: using a flat 54.4mm tamper


----------



## Rickv (Nov 18, 2019)

Skizz said:


> Thought I'd sorted my brass block issues (used with IMS screen) by enlarging the holes, adding two more in the middle and countersinking the outlets to reduce velocity. Problem-free for a couple of months until I descaled two days ago and now I'm getting a deep crater in line with the rearmost left hand hole and noticeable channelling. Rotating the screen makes no difference. No idea why the problem has come back (and worse than it was) but honestly cant think of anything else to try.
> I think the broader issue is that the aftermarket brass and stainless blocks are designed for the commercial Gaggia machines rather than the Classic which, has a single, off-centre inlet point as opposed to centred or multiple inlets. This causes uneven pressure across the dispersion block, leading to the jetting/cratering issues we all know about. This is compounded by the IMS screen, which allows these jets to pass straight through without slowing. Have ordered an original pattern screen and hoping the fewer and smaller perforations will do the trick.
> For reference, I'm dosing 18g into an 18g VST basket and running the machine at 9.5 bar static.


I upgraded to the brass block and ims screen which I've used for a few months. Every time I remove the screen to clean behind it I end up spending ages trying to get the screen lined up just right so it doesn't spray from just one side. Gave up faffing and put the original screen back in with the brass block. Instantly fine, no more spritzing water every where and no more channeling.

Sent from my iPhone using Tapatalk


----------



## Agentb (Feb 11, 2017)

Rickv said:


> so it doesn't spray from just one side.


 I don't get that, i get "dimples" from each corner - if that makes sense, and if it's annoying me it takes 10 seconds maybe to rotate it a half a hole.

I'm now wondering are we talking about the same IMS screen (mines a GA200NT) or if maybe the screens are easily damaged perhaps - these flatter IMS ones feel more fragile than the concave originals and they have to sit perfectly flat. Anyways i promised some photos.








Not sure this picture here helps but you can see the part number








This is a ridged (yes i ordered the wrong one) VST 18g with 17.5g dose - you can see th ridge line.

and







Trying not to get the phone wet...








Normally I'd give it a few seconds before removing the PF, you can just see the dimple at 2 oclock...

TBH I'm not much convinced about anything you see on the top of the puck short of a crater, as the solenoid action sucks a lot of fluid and that suction would be mostly around where the dimples are. I've never seen (assuming the grind is set correctly and the prep is good) weirdness at the business end. ???? hth.


----------



## Rickv (Nov 18, 2019)

Agentb said:


> I don't get that, i get "dimples" from each corner - if that makes sense, and if it's annoying me it takes 10 seconds maybe to rotate it a half a hole.
> I'm now wondering are we talking about the same IMS screen (mines a GA200NT) or if maybe the screens are easily damaged perhaps - these flatter IMS ones feel more fragile than the concave originals and they have to sit perfectly flat. Anyways i promised some photos.
> 
> 
> ...


Mines a GA200 IM. Maybe thats why it sprays.

Sent from my iPhone using Tapatalk


----------



## Agentb (Feb 11, 2017)

Rickv said:


> Mines a GA200 IM. Maybe thats why it sprays.


 If you don't want it ... 😹


----------



## Agentb (Feb 11, 2017)

IMS's website https://www.imsfiltri.com/ has the NT as being a non stick version

"NANOQUARTZ

IMS has developed a high quality
coating to further improve the
surface of its filters using quartz
nanotechnology, the NANOQUATRZ
coating.
Thanks to its high non-stick
poterty 😹, this coating makes it
easier to remove used coffee
cakes,😹 and it also makes it
easier to clean thereby rendering
the antibacterial nature of the
surfaces extremely effective."

There is nice little youtube showing the baskets and filters being made. 👍

My cakes are easy to remove... 😹


----------



## Skizz (Feb 10, 2020)

Weirdly enough, a week after descaling and with no further adjustments to the IMS screen my shots have cleaned up and the channeling issues have largely gone again. Even the divot from the solenoid take-off has got shallower, to the point of almost disappearing. The original replacement I ordered arrived today so swapped it for the IMS and while the shot looked comparable the solenoid divot was far deeper and more pronounced and there's now a visible indentation from the screw. Go figure


----------



## Agentb (Feb 11, 2017)

Skizz said:


> and more pronounced and there's now a visible indentation from the screw.


 If you put a 5p piece on the top of the tamped cake - lol - and close and re-open the PF does it cause an indent? If so try dosing a bit less and see if that changes. I have noticed today using some pacamaras 😺 after some Rwandan peaberries i have to grind a bit finer and they certainly seems to fill the basket noticeably more, to the point of thinking - i may need to reduce the dose down to 17g i know 18g would be close.

The original screens protrude further so more likely to make contact than the IMS.

If you swap the brass shower head for the original does it go away? I looked again closely at the pictures of the countersunk holes and they are getting very close to the outer edge - it should not make a difference but maybe it does.

The other maybe, is the puck is being lifted up as it de-pressurises? 👍


----------



## Skizz (Feb 10, 2020)

Agentb said:


> If you put a 5p piece on the top of the tamped cake - lol - and close and re-open the PF does it cause an indent? If so try dosing a bit less and see if that changes. I have noticed today using some pacamaras 😺 after some Rwandan peaberries i have to grind a bit finer and they certainly seems to fill the basket noticeably more, to the point of thinking - i may need to reduce the dose down to 17g i know 18g would be close.
> 
> The original screens protrude further so more likely to make contact than the IMS.
> 
> ...


 Great sanity check, thank you. On the same beans that left no mark with the IMS screen but will check with a 5p tomorrow. Spotted the more pronounced dome on the screen this evening so reckon you're right about that being the culprit. Not sure why it would increase the solenoid divot though as would've thought the smaller holes in the screen would offer more resistance to the end of shot suction.

Not got an original plate to compare against as it was so grim when I got the machine that I binned it. There's no leaking at the edge of the screen as made sure there was sufficient surface area left on the rim of the plate to get a good contact all round. No evidence of the fracturing you'd expect from the puck lifting either, and its well seated in the basket after the shot.

Slings and arrows of outrageous shower screens, eh?

PS. No need to brag about the Pacamara 😄. Still regret not buying more of Crankhouses Las Margaritas when they had it. It was incredible!


----------

