After about 4 months of not being used (I was away), I booted up my Mozzafiato the other day and started brewing shots. Seems like something might be up with the brew pressure line. The pressure gauge shows 9 bar when the pump is operating - even without the portafilter attached. Hot water is flowing freely from the group head and the pressure reads 9 bar. This doesn't seem right - if there is no resistance to the brew water flow, how can there be pressure? The machine is plumbed in to the mains water supply downstream of a BWT filtration system. But just wondering if a valve or solenoid inside might be jammed? The exact model is a Mozzafiato Cronometro R.

Many thanks.

thanks for the reply but i guess I don't understand. i thought the brew pressure gauge was supposed to indicate the pressure of the brew water bearing down on the coffee puck. more coffee/finer ground coffee/more densely tamped coffee = higher pressure etc. without a coffee puck by definition there is no resistance and no pressure. the water freely flows out of the rotary pump through the group head and into the drip tray. if the brew pressure gauge shows 9 bar without any coffee, what pressure exactly is it measuring? and what changes when we do have coffee in the portafilter? sorry if these are silly questions!

SiliconLunch wrote:thanks for the reply but i guess I don't understand. i thought the brew pressure gauge was supposed to indicate the pressure of the brew water bearing down on the coffee puck.

No, your pressure gauge capillary tube is on the manifold right after the pump outlet, so it measures pressure at that point. Some pressure profiling machines have gauges that do measure at the brew chamber, otherwise to get measurements of the pressure at the puck people often use a device like a Scace II or similar rig that measures pressure there while water slowly flows through a simulated puck.

SiliconLunch wrote:without a coffee puck by definition there is no resistance and no pressure. the water freely flows out of the rotary pump through the group head and into the drip tray.

You are missing the effect of that gicleur that I mentioned earlier. It's a tiny nozzle that the water must flow through before it gets to the brew chamber above the puck. There are some pics in this thread: Stainless steel E61 mushrooms

Thanks for trying to explain.

I have 2 other espresso machines (ECM & Lelit) and the pressure gauge doesn't work like that. With no coffee in the basket and the pump running the indicated pressure is zero. When backflushing using a blind filter basket, when I operate the pump I observe the pressure quickly rises from zero up to my preset maximum brew pressure (8-10 bar), hold steady there, then drop back to zero when the brew lever is lowered and the water is flushed out.

I think I need to learn more about the plumbing of my Rocket. I'm afraid don't understand the function of this gicleur. Fine, I get that it's a tiny nozzle in the E61 the water must pass through but I would expect it to create only an insignificant 1-2 bar pressure. If it creates a 9 bar pressure without anything on the other side, doesn't that indicate it's blocked or scaled up?

And if this is normal, then how does one go about setting the brew pressure on this machine? It seems that the minimum pressure I can set is already 9 bar (as created by the gicleur) - it can only go higher?! Again something doesn't sound right...

I tried a backflush with a blind filter basket and the pressure gauge shows exactly the same thing as when there is no portafilter at all. I am almost certain this is not how the machine worked when it was new, else I would have noticed it immediately.

Here's a video of the machine doing its thing: Anyway I have a friend with a similar machine and I have asked him to run the same experiment. Also might run it past the dealer. Might also have a play with the brew pressure setting screw on the machine to see whether that changes anything. And possibly tweak the mains pressure supply too.

Thanks for helping.

Homeburrero's explanation is as good as any. It's what you'll see on and Rocket with the R pump. This is why flow control kits include the gauge to display pressure at the head. The pump is always putting out more volume than the gicleur can pass, thus the pump gauge is always going to show the pressure at the pump outlet as what the pump bypass is set to. No need to change the bypass setting unless you want a different maximum for some specific coffee roast you're trying.

You are also correct about the functioning of the other machines, the ECM with a pump of much lower flow and the Lelit with a gauge measuring at the brew-head.

SiliconLunch wrote:I get that it's a tiny nozzle in the E61 the water must pass through but I would expect it to create only an insignificant 1-2 bar pressure.

I think your expectation is in error. Pushing 9 bars against a 0.7 mm nozzle should allow a flow of only about 1 liter per minute, which is about par for the water debit that people measure in these machines. (Here's a handy online calculator for sprinkler nozzles: http://irrigation.wsu.edu/Content/Calcu ... ements.php )

SiliconLunch wrote:And if this is normal, then how does one go about setting the brew pressure on this machine? It seems that the minimum pressure I can set is already 9 bar (as created by the gicleur) - it can only go higher?!

SiliconLunch wrote:Might also have a play with the brew pressure setting screw on the machine to see whether that changes anything.

It's very easy to adjust on your machine per the owner's manual. When people see a change in their brew pressure it's sometimes a case where the adjustment locknut was loose and the setting changed. You should be able to set it higher or lower -- this screw adjusts the bypass on the rotary pump head.

You can also remove the topmost nut of the group and the screen, then use a 7mm socket or nutdriver to remove your gicleur to make sure nothing there is clogged.

If you don't understand it, it might be best not to adjust things.

Your pump gauge is simply displaying how much higher the pressure is in the manifold over atmospheric. The manifold in question is where the various circuits branch off, the single pump in question is the pump which supplies both circuits, steam and brew.

When doing a boiler fill from cold, the pump is pumping past a 2-way solenoid valve. The fact that the gauge shows the pressure at the manifold does not mean that whenever the boiler is filling, the machine is brewing at somewhere from 4 to 8 bars. It's simply displaying the pressure at the manifold which is higher than the atmospheric pressure of the cold boiler because the orifice of the solenoid valve is small.

If it were able to put 50GPM into the boiler don't you think the breather valve would slam shut?

homeburrero wrote:You can also remove the topmost nut of the group and the screen, then use a 7mm socket or nutdriver to remove your gicleur to make sure nothing there is clogged.

Thanks Pat I will be doing that next.

homeburrero wrote:It's very easy to adjust on your machine per the owner's manual. When people see a change in their brew pressure it's sometimes a case where the adjustment locknut was loose and the setting changed. You should be able to set it higher or lower -- this screw adjusts the bypass on the rotary pump head.

So I consulted the user manual about setting the pump pressure. Thanks for bringing my attention to it. The manual is careful to say it is "pump pressure" we are seeing at the gauge not "brew pressure". Of course then this confirms the need for a Scace device to get exact temperature and pressure readings at the group head.

But I am still a little confused as to how to set a lower pressure. So for example, I want to adjust my machine to get a brew pressure of 7 bar because I have a special need for a particular bean and/or roast. I install the blind filter, loosen the locknut and turn the pump pressure screw anti-clockwise (to decrease the pressure), all as are stated in the manual. But if the gicleur is creating 9 bars of pressure as measured at the pump output, then how can I measure a pressure < 9 bars at the head, without a Scace device? It seems like quirky to me !

Anyway, just to share some extra data points: I asked 2 friends of mine who also have the same Rocket to run the pump without a portafiltter attached and note the pump pressure gauge. One of them read 1-2 bars of pressure while the other one read 10 bars ! I haven't followed up yet to note whether their machines are plumbed in or not and confirm they have the rotary pump.

I'll update the thread with my findings.

Cheers.
Nico

SiliconLunch wrote: then how can I measure a pressure < 9 bars at the head, without a Scace device? It seems like quirky to me !

Anyway, just to share some extra data points: I asked 2 friends of mine who also have the same Rocket to run the pump without a portafiltter attached and note the pump pressure gauge. One of them read 1-2 bars of pressure while the other one read 10 bars ! I haven't followed up yet to note whether their machines are plumbed in or not and confirm they have the rotary pump.

If they have the same machine as yours, then it has the same pump.

If you set your pump pressure to a maximum of something you want, say 8.5 Bar, then you know the pressure in the brew circuit when it's brewing can never exceed 8.5 Bar and that your coffee grind, tamp and prep is the only real contributing factor to the flow/pressure through the brew chamber... Re-reading this I see I'm not saying exactly what I am trying to say... The pump makes sure there's more than enough flow to keep pressure steady before the gicleur, wherever you've set the maximum pressure via the pump's bypass. The gicleur is making sure that there is a maximum flow through the brew chamber, it's much higher than you'd ever want to be brewing, thus the coffee prep is important. The coffee "puck" becomes the major pressure drop in the system, it's a more significant pressure drop than the gicleur with proper grind and dose, and that's why the machine can make great coffee.