Rocket Giotto - Problem with Grouphead Pressure

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
LaNovice1982

#1: Post by LaNovice1982 »

Ok, I just received my Rocket Giotto Cronometro R, everything seems ok but when I pull a shot the pressure goes up to 9 bars but when its done the gauge rest at 4 bars. May seem petty but I'm thinking something has to be wrong, I tried contacting where I bought it and of course it will be 5 days until they can get back to me. If anyone has any ideas it would be greatly appreciated, thanks in advance!
Brian H.

Giampiero

#2: Post by Giampiero »

Are you plumbed in or are you using the water reservoir as water supply?
If plumbed in the gauge should read the inlet water line pressure.
Maybe even if you are using the water reservoir the gauge could not goes to zero if it's connected in a position where still read some trapped pressure between the HX and a check valve.

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HB
Admin

#3: Post by HB »

LaNovice1982 wrote:...when I pull a shot the pressure goes up to 9 bars but when its done the gauge rest at 4 bars.
That's 100% normal. TL;DR - it's due to the water expanding when heated in a closed system. The longer answer from What is normal pump pressure at idle? in the FAQ:
HB wrote:The pressure reading when the machine is idle isn't important.

To elaborate, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the boiler [or heat exchanger] warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. For vibratory pump espresso machines, the expansion valve (traditionally called an over-pressure valve in this context) is set to open at the desired maximum brew pressure, usually around 9 bar. This valve vents water into the driptray to avoid subjecting the hydraulic system to excessive pressure. It only needs to let a few drops of water escape to reduce the pressure sufficiently.
Dan Kehn
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homeburrero
Team HB

#4: Post by homeburrero »

As others have said, that is normal.

I'm pretty sure the brew circuit hydraulic on the Giotto is: water line -> solenoid valve -> pump -> gauge -> check valve -> expansion valve + HX / thermosyphon -> brew valve. So on these machines you may or may not see residual pressure at the gauge after brewing or backflushing. Nothing to worry about.

The pressure you see at the gauge when the machine is idle might be zero even if on a plumbed-in machine because the gauge is between that solenoid valve on the water input line and the check valve before the HX. It can be more depending on the residual pressure at that point when the pump, solenoid, and brew valve were shut off.

Between the check valve and the brew valve you have an HX that is completely filled with water, which does expand slightly when heated, and since it is not compressible that tiny expansion while idle (brew valve closed) can create high pressures. This expansion pressure is not reflected on the Giotto's gauge. If the expansion valve is doing its job, it will open and let a few drips out to keep that HX pressure below 12 bar or so.
Pat
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LaNovice1982 (original poster)

#5: Post by LaNovice1982 (original poster) »

Wow so much information, you guys are awesome! I wish I could post a video here, im coming from a Breville Barista Express and I feel like I've never used an espresso machine after using this Rocket.

First I'm am not plumbed in, I'm using the tank for now. Also the machine will be at 0 bars when it turns on but when I do a 3 second flush the group head pressure rest at 4. I have been running some hot water and that will lower it back to 0 bars, but I really appreciate you guys getting back so fast and easing my anxiety lol. I look forward to maybe helping others on here!
Brian H.

JRising

#6: Post by JRising »

Bring the brew lever down slowly, give the machine a moment as you pass center for the pump to stop before the brew valve shuts, you should trap less pressure. Bring it down quickly and you can trap a lot.
If you want to, you can adjust the brew button (the push button behind the lever) further into the machine so it turns on slightly higher into the raised position and turns off sooner as the lever is brought down... But see how it brews as it is, before making changes. Get a feel for it before deciding it isn't right.

LaNovice1982 (original poster)

#7: Post by LaNovice1982 (original poster) »

This makes so much sense! I just turned my machine on and it's warming up now, I'm going to try this and I'll let you know. I truly thank you so much for this tip, whether it works or not it makes a lot of sense!
Brian H.

LaNovice1982 (original poster)

#8: Post by LaNovice1982 (original poster) »

Btw this actually worked! When I pushed lever down slowly it will drop pressure down to 0 right before the midway lock . Also if you push lever all the closed and it's still reading pressure I can bring the lever to the halfway point and then pull slightly as if your pre infusing and the pressure will drop to 0. Now I only wonder if it's supposed to have pressure since when operating normally it leaves pressure.
Brian H.

JRising

#9: Post by JRising »

LaNovice1982 wrote:Now I only wonder if it's supposed to have pressure since when operating normally it leaves pressure.
It absolutely doesn't matter. The gauge is there so that if something goes wrong while brewing you can look at it to confirm that the pump is doing something when running. What the gauge shows when the machine is idle is irrelevant.

LaNovice1982 (original poster)

#10: Post by LaNovice1982 (original poster) »

Awesome, thanks for the reassurance!
Brian H.