Rocket Cellini Brew Pressure Adjustment

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mobiletrevor
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Joined: 3 years ago

#1: Post by mobiletrevor »

I am hoping for some instructions on how to adjust my Rocket Cellini's brew pressure. I have searched many posts and not found a working solution yet. Currently my unit reads between 7.5 and 8 bar during the brew process. I would like to adjust it to 9 bar. If anyone has a write up or process for adjusting that would be great as I do not have a shop near me that I can take the machine to for adjustment.

Thanks

JRising
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#2: Post by JRising »

Mainly adjust your grinder, the coarser the grind, the less resistance to flow thus faster flow and less pressure drop across the puck.
Your machine does have an OPV that will limit the maximum pressure that your pump can force into the system, you can tell the OPV apart from the expansion valve because the OPV can be closed off from the system by that little ball-valve on the floor.

So. To make it less uncomplicated (Sorry), there's an expansion valve (The big one) to prevent the boiler from rupturing when the boiler heats(It simply is forced open to relieve at a set point, 12Bar to 14 Bar or something, doesn't matter), no need to mess with it if you think it works. There's an OPV that will limit the maximum pressure in the brew circuit (It simply is forced open to relieve at a set point, 8.5-10.5 Bar depending on what you're trying to explore with different maximum pressures). And, of course brew pressure, set by the resistance to flow at the brew chamber, your machine has proper full sized portafilter baskets and is forgiving enough to allow one to learn by trying.

Of course, nothing in the brew circuit has anything to do with the pressure gauge or the pressostat or other boiler controls and such.

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HB
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#3: Post by HB »

To clarify, there's two types of pumps: Vibratory and rotary. Your Cellini appears to have a vibratory pump, according to DaveC's Cellini Classic - A Closer Look:



You adjust the maximum brew pressure by adjusting the over-pressure valve (OPV). See the FAQ How can I adjust the brew pressure of a vibe pump espresso machine?

FYI, here's a breakdown of an OPV. It's a pretty simple mechanism:


From La Marzocco GS3 Leaking

The "valve assembly" above is threaded to allow the "hose connection" part above to change the compression of the spring, thereby increasing/decreasing the closure pressure of the "OPV body" part above (not sure I agree with this labeling, but whatever). More spring compression = less water escapes => higher brew pressure, less spring compression => more water escapes => lower brew pressure.

For completeness, the FAQ includes instructions on adjusting rotary pumps, too: How to adjust brew pressure of rotary pump espresso machine?
Dan Kehn

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homeburrero
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#4: Post by homeburrero »

If yours happens to be a Cellini classic , then it's easy -- you have one OPV that you can adjust. But some newer vibe pump Rocket models have two 'OPV' valves, as JRising mentioned. One is an expansion valve that is set fairly high, and the other is used as an OPV to limit the max brew pressure from the vibe pump. This thread should help if your Cellini is one of those: Rocket Giotto Type V brew pressure inconsistency/adjustment (Note: The innards of Giotto and Cellini of the same year and model are identical. )
Pat
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