Is the practical pressure limit of the ROK 6 bars?

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DamianWarS
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#1: Post by DamianWarS »

I saw an upgrade for the ROK Presso to have a pressure gauge added so I bought the kit, dusted off my ROK presso and added it. I was surprised to see that I could only achieve about 6 bar pressure before it started to leak around the silicone dispersion screen. It felt quite hard to go much further too, I've used other direct pressure levers but you had to exert a lot of force for the ROK to get it close to 9 (plus it leaked a whole lot) so 6 bar is really the practical pressure limit. So I bought the competition shower screen thinking it was better at sealing, it's more of a silicone ring fitted around a metal shower screen. It had the same limits too and at +6 bar it starts to leak. I decided to push it a little harder and it broke the flange that holds the PF in place and made quite a mess (I might have been too fine of grind) fortunately, you can replace these flange rings as separate parts and they are not all that much money, so I'm going to replace it to get it back to working condition.

Does anyone else have the pressure gauge kit with their ROK? can you confirm the same thing that the practical pressure limit is about 6 bar? I'm concerned the gauge is off since ROK themselves advertises you can hit 9-10 bar very easily. I can hit 6 easily and I can push it harder but it's not worth it since it leaks so much. 6 bar is still functional but I'm just surprised at how quickly it peaks before it starts to leak. I have the Flair58 too and the experience of the Flair58 is simply at a different level and I have no problems reaching 9 bar without needing to exert huge amounts of force.

benhb

#2: Post by benhb »

Hi Damian,

ROK owner here and very interested in the pressure gauge kit.

Is this the kit that's available in SE Asia for the current ROK Espresso GC or a kit for the original Presso (clear pressure chamber)?

Bluenoser

#3: Post by Bluenoser »

I tried out a ROK GC a few years ago. And it leaked whenever I put a lot of pressure on it. I didn't have a pressure gauge but I would guess that anything more than five or six bars. Now the distributor said it was defective and he replaced a few parts and said it worked better. But we went with the flair V2 at that point.

pachint

#4: Post by pachint »

Just purchased the ROK GC pro with the pressure gauge installed. Had the same problem when only using the naked portafilter, above 6 bars there was a hissing sound and leakage around the shower screen seal.
Asked the distributor and they told me the naked portafilter is using the old version and i got the old chamber version. They changed the chamber and it works totally fine without leakage but the portafilter lock position is slightly more to the left. Turns out you can check and do some sanding on the chamber. Here's the link to the video : http://www.youtube.com/watch?v=JXIKjLfoDH8

benhb

#5: Post by benhb »

Hi Michael,

Thanks for the report about the new chamber and thicker shower screen.

Are you able to achieve pressure between 6 and 9 bars or does it seem to max out around 6?

pachint

#6: Post by pachint »

I could easily get 9-10 bars of pressure without leakage or hissing sound. Any of you guys could get more than 30g yield in 1 press? I found that i could only get 30g yield with 16g dose in 1 press :?

benhb

#7: Post by benhb »

Very nice! Great to hear 9 bars is easy & without leaks with the GC Pro setup. Thanks for confirming.

Re: output in a single press...

I can get about 43-45g in a single press. I aim for 34g out on a 14g dose and there's a bit of lever room left at the end of shot pull (about an inch away from end of lever travel). Side note: I'm using a metal dispersion screen on top of puck, bottom paper filter and an IMS basket on my current ROK setup. But even before with a fully stock ROK GC, I could get the same max output (43-45g) from a 15g dose on a single lever press.

I'm wondering what could be restraining output to 30g or less...

I've seen some photos of the piston on the GC pro with the gauge at top and pressure tube traveling through middle of piston (at the bottom). I'm not clear how different the water capacity is with it vs. the non-pro piston and if that's related.

And just to double check, you're filling water right up to the rim before pull (say 1-2mm from top)?

thecoffeefield

#8: Post by thecoffeefield »

6 or 7 bars is the max. I had the "somedaysomehow project" kit, purchased it from him directly on Instagram and shipped from Indonesia. He swears that he tested hit kit and that it achieves 9 bars without leaking but it's not the case. Fair to say that I sold it and just went with the Flair 58. I hated having different size baskets and accessories anyways.

pachint

#9: Post by pachint »

I filled the water at almost to the top as you described it, also the seller mention the connection arms length changed in the new model to provide more easy push, maybe that could be the cause.
Do you use ims 49mm basket? How does it fit the portafilter? I'm interested to upgrade my filter basket

benhb

#10: Post by benhb »

Hi Michael,

Ah, that's interesting information re: arm length changing. Did the seller mean the arm length is different on the GC Pro model vs regular GC or from the old Presso vs the new GC models? I believe the GC Pro piston with pressure gauge & tube is a direct retrofit onto the current GC chamber, but I could be mistaken.

The basket I'm using is the one on page 34 of the IMS competition catalog with model number: B602TH25

The outer rim diameter is 60mm, inner diameter 52mm and height is 25mm (it's available in 29mm height, but that won't fit ROK spouted portafilter, but perhaps the naked? Not sure). The IMS basket slides in & out of the ROK portafilter without any resistance at all, so it definitely fits inside. The trouble is keeping it there.

As someone on a reddit forum suggested I used an uncurled paperclip instead of the stock spring retaining wire from the stock basket, which has a ridge for the wire. The IMS basket has no ridge for a wire and I couldn't fit it with the stock wire clip, which sticks out a fair amount from the portafilter walls due to its bends.

I'm hesitant to suggest the paperclip solution because it's an ultra tight fit with the IMS basket. I had to really lean into it to get the basket in with the paperclip. I'm pretty sure I'll need to use some sort of hardened steel lever to get it out. Perhaps a wide-flat rubber band around the basket might provide just enough width & friction to keep the basket in place when knocking out.

As a side note, the puck slides out the IMS basket much easier than from the stock basket. The IMS steel is polished, smooth and clean so I think there's less friction holding the puck in. 8 times out of 10 I just invert the portafilter, give it a single shake (not knocking on anything) and the puck will drop out.