OPV on Rocket Cellini V2 is confusing.

Need help with equipment usage or want to share your latest discovery?
hansing80

#1: Post by hansing80 » Dec 28, 2012, 1:35 am

Dear members,

Hello.
I've been using Rocket Cellini V2 for 6 months.
The brew pressure gauge is always indicating 10 bar when I pull a shot.
If I grind coarser, the shot goes fast(2 oz for 20 seconds), but the gauge indicates 10 bar.
It also indicates 10 bar with blind filter.

10 bar is not bad, but I feel the taste is a bit strong.
So I tried to lower it by adjusting OPV.
I opened the cover.

Here is a picture.

Image

I guess OPV is in white circle.

The mystery is a black valve in blue circle.

So I e-mailed Rocket, questioning the function of black valve.
Here's the reply.
The valve you mention is solely for the pump pressure gauge on the vibration pump machines.
Closing the valve allows for the technician to correctly set the expansion valve
As a vibration pump pressure is regulated by the expansion valve setting, a pump pressure gauge is not strictly necessary. This valve allows the by pass to be correctly set while indicating the pump pressure. The valve should be set as it was when you received.
But I cannot understand the black valve's function.

Any comment will be appreciated.

User avatar
erics

#2: Post by erics » Dec 28, 2012, 1:01 pm

I would tell you that their explanation is not complete as they should have also spoken about the check valve/secondary relief (?) next to the ball valve which allows a portion of the pump flow to travel back to the "baby" reservoir.

I believe this is part of their dual preinfusion system but need to do a little thinking on that one. I would be curious as to who at Rocket sent you the return email.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

Link

#3: Post by Link » Dec 28, 2012, 2:10 pm

To the OP, were you able to adjust the brew pressure ? I'm about to buy a machine and the rocket is in the top 3 but I'm a total newbie. to these machines and thought a machine in that price range would allow easy adjustment on something that seems so important to the espresso taste.
Thanks

hansing80

#4: Post by hansing80 » Dec 29, 2012, 1:31 pm

Eric
That was Mr. Andrew Meo who sent me the reply.

User avatar
erics

#5: Post by erics » Dec 29, 2012, 1:41 pm

I will post a more complete explanation (well . . . my version) later on but I would send him a link to this thread and see what he can add.

I believe that during the 25 seconds +/- of the typical brew cycle, a portion of the pump output is intentionally diverted through the ball valve and check/relief(?) valve back to the small reservoir. This lessens, possibly eliminates, the function of the OPV during that time frame. Yes, it gets complicated.

Larry - this should, in no way, alter any decision process you have. The Rocket is a nice machine, as are many others.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

hansing80

#6: Post by hansing80 » Dec 29, 2012, 2:08 pm

Link wrote:To the OP, were you able to adjust the brew pressure ? I'm about to buy a machine and the rocket is in the top 3 but I'm a total newbie. to these machines and thought a machine in that price range would allow easy adjustment on something that seems so important to the espresso taste.
Thanks
I am still trying.
When I closed the black valve, the brew pressure was about 12bar with BF.
As I adjusted the OPV, the brew pressure went down by about 11bar.
I have not tried to 9bar.

The interest thing is that when the black valve is open the brew pressure gauge indicates 10bar even if the OPV setting is 11bar or 12bar. The black valve limits a brew pressure by 10bar.

I am not sure whether the black valve still works or not at 9bar of the OPV setting.
I am going to try it ASAP.

FYI, the pump pressure is not same with the actual brew pressure, so if the pump pressure gauge indicates 10 bar, the actual brew pressure could be low than that.

User avatar
erics

#7: Post by erics » Dec 29, 2012, 8:07 pm

The "black valve" is simply a ball valve that is designed for either open or shut operation. If you close the ball valve and adjust your OPV such that a blind filter produces 9.0 bar on the gage, you will be "adjusting and operating" your machine as is typical of all E-61 Hx machines.

Keep the ball valve shut and operate the machine that way for a few days. Your brew pressure should then NEVER exceed 9.0 bar during normal operation.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

hansing80

#8: Post by hansing80 » Dec 30, 2012, 12:49 am

Well, I simply got a 9bar pump pressure by adjusting the OPV. The ball valve does not affect the pressure gauge when the OPV set for 9bar. It affects the pressure gauge only when the OPV setting is higher than 10bar. As I lowered the OPV setting by 9bar, the pump pressure gauge is at 9bar whether the ball valve is closed or not.

I guess the manufacturer designed the valve for users to get simply the proper brew pressure with no need to adjust the OPV.

Link

#9: Post by Link » Dec 30, 2012, 6:28 pm

erics wrote:Larry - this should, in no way, alter any decision process you have. The Rocket is a nice machine, as are many others.

Thanks Eric, (I'm obviously speaking with no knowledge here) after seeing your post I read up on OPV's one thing I'm missing is if the ideal brew pressure is around 9 bar why are a lot of these machines set higher by the manufacture ? I read one article on a blind tasting where brew pressures were 7-9 bar & 11-12 bar they could not tell any taste difference in the 2 groups but could tell the difference between the 2 groups which seems like there's some wiggle room in brew pressures. I think the Rocket is a beautiful machine and had hard time picking but budget won out & I just ordered a Bezzera Magica and a Lelit grinder. So in a few weeks I'll still have very little knowledge but I'll have a great source of caffeine to keep me going ! I also saw youtube video of a pressure gauge on an e61 GH the video was comparing the machines gauge to the GH gauge both gauges read 12 bar and stopped there. I'm not sure what the point of that test was.

hansing80, looks like you got figured out. Do you notice any taste difference from your 9 bar brew pressure ?
Thanks
Larry

User avatar
erics

#10: Post by erics » Dec 30, 2012, 7:31 pm

The reason why I said
Your brew pressure should then NEVER exceed 9.0 bar during normal operation.
is that the OPV adjustment sets the maximum pressure one would realize.

Yes, there has been a lot of threads as regards brew pressure and an equal number of OPV adjustment scenerios. There is enough written word to form the basis for a multi-page tech tip book.

Keep in mind that manufacturers not only generally outsource OPV's but their machines are sold worldwide with vibration pumps having slightly different performance curves depending upon their voltage/frequency. You can add to that brew pressure gages of typical +/- 6.0 % accuracy and dubious quality. Isn't this fun? :)

Whether or not individual manufacturers make specific adjustments to their machines on the "final" assembly line is really unknown. I sorta THINK that every machine is powered up and brewed with a blind filter amoungst other tests. If the pressure is between x and y and there are no leaks, all is well. Machines which can accept the ESE pods must be set to 11 bar (if I have my facts straight).

As regards your Bezzera Magica, know that it has the same boiler as the Bezzera Strega or vice versa and a complete parts list is available here: http://www.bezzera.it/index.php?lang=en . Take a look at the last page of the "accessories" pdf and you will see that Bezzera offers a 9.0 bar "kit", well . . . maybe not for the Magica. However, you will be enthralled with the assembly quality.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com