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Brew pressure profiling with front panel controlled dual OPV

Postby fransg on Wed Mar 13, 2013 5:50 pm

This morning I took my Rocket Giotto to visit Peter van der Weerd (from http://www.kafko.nl) in his espresso machine workshop:

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He has made me a temperature probe to fit in a portafilter basket:
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But since I was there anyway, he took an extra back panel and cut out a square so I could change the setting of the OPV while working with the machine. This way, I wouldn't need to disassemble the covers if I wanted to change the brew pressure setting:

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I had been lowering the brew pressure on the OPV but noticed that it would leak water when turned down below 8 bar. Here a few images of this original OPV connection:

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To be able to easily change the setting of this OPV through the back panel opening, Peter created a bend in the spanner:

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An image of the spring inside this OPV:

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Peter could cut the spring to allow the threaded part to go in deeper but he didn't like this idea as the spring has its own use and characteristics.

Still, the threaded part needs to go in deeper to be able to turn it out a number of turns before the rubber gasket leaves the space it fits in to close it off. Turned back more, it enters the threaded room and water seeps through.

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Peter made the OPV a little deeper:
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Now, it would be possible to lower the brew pressure without leaks.

At this point, Peter discussed an idea he had been thinking about for a while: why not create an optional extra OPV, with a solenoid valve, controlled from the front panel, switching between two very different OPV settings during any extraction? You could start the extraction, building up the pressure calmly to 6 bar, then briefly use 9 bar and finish the extraction at 6 bar again, for instance, or any thinkable combination. And both settings could be adapted independantly.

One would need something like this:

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I liked the idea very much so Peter set forth:

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To control the new solenoid, the on/off light was sacrificed for now (we can install it in another place later) and an identical switch as the original Rocket on/off switch was installed:

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The second OPV got wired too. After first having it use the mains power from the on/off switch, Peter changed this. Now it is only active when the vibe pump is active. This way, if the solenoid OPV selection switch is "ON" and selecting the lower pressure OPV, the solenoid will only be ON when the pump is ON too, and won't be ON for long periods of time if the machine is idle.

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Setting the new OPV to 6 bar involves temporarily disconnecting the back hose/plug, adding a temporary hose and changing the setting using a long slender screw driver:

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The tube prevents water from the OPV flowing into the machine.

Next the tank went temporarily back in for testing, the machine was blow dried and we did some testing to see if there were any leaks (none).

In these first test, the espresso was delicious so I look forward to play more with this dual OPV setup!

The switches on the front panel are very straightforward: the top is ON (up) / OFF (down) and the lower switch is HIGH-9bar (up) / LOW-6bar (down).

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One last picture of Peter satisfied after a number of hours of work and play! I want to thank Peter for his time, his enthusiasm, help and his inventiveness.

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Postby erics on Wed Mar 13, 2013 7:48 pm

This morning I took my Rocket Giotto to visit Peter van der Weerd in his espresso machine workshop

And everybody should have a shop such as that in their locale . . . you are very fortunate.

BUT - it seems that something else is amiss to not allow the lowering of the brew pressure without causing a leak. Especially given the existence of their (Rocket's) secondary preinfusion "gizmo".

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Postby fransg on Thu Mar 14, 2013 4:26 am

I must confess I have no idea what that switch is doing there. Do you know? Is there documentation about it?

PS: I now see there's something about it on
OPV on Rocket Cellini V2 is confusing. and at my settings of 9 bar and below, it seems the black switch can be ignored.

Anyway, with the modifications made yesterday, lowering the brew pressure does not cause any leak, with or without the dual OPV mod.
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Postby erics on Thu Mar 14, 2013 8:10 am

. . . it seems the black switch can be ignored.

It should not be "ignored". The first component is a simple ball valve. The second component is, I BELIEVE, a spring loaded check valve which may be adjustable. As you can see, it discharges back to what I have always termed the "baby reservoir".

I did send an email to Rocket some time ago inquiring about it and may do so again.
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Postby fransg on Thu Mar 14, 2013 8:22 am

What I meant was that whatever it does, the "mystery switch" as it sits now is not disturbing the working of the two OPV's installed. The built in brew pressure gauge and the one that can be attached to the E61 both agree that the pressure is 9 bar when the front panel switch is up and 6 bar when the front panel switch is down (causing the new solenoid to be activated).

The black mystery switch was also not causing the leak earlier: it was obvious to see that if I turned the nut with the rubber ring outward far enough, droplets would seep out the thread, as the rubber ring was not in the front end anymore, so not completely closing off the inside.
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Postby fransg on Thu Mar 14, 2013 8:27 am

PS I got a PM asking if the same mod with dual OPV's could be done in a rotary pump machine. I asked Peter and he says sure, this is basically the same thing, the connections would be a little different but no big deal.
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Postby HB on Thu Mar 14, 2013 8:59 am

Eric would know for certain, but wouldn't that depend on the type of bypass valve on the rotary pump? That is, the over-pressure valve for a vibratory pump directly affects output pressure by changing the effective flow rate; a rotary pump's output pressure isn't affected by flow rate at espresso pour volumes.

On the other hand, a rotary pump's output pressure is directly affected by input pressure, so you could fashion a similar mod using two input line pressures (one from the mains, one through a pressure regulator). Hmm-m, that could be a fun experiment.
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Postby 4000ft on Thu Mar 14, 2013 9:58 am

You wouldnt need two OPVs with a rotary pump machine, just the lower setting one, the bypass valve doing the job of the higher set OPV. It would work the same in the end but with alot more flow out of the added OPV (and into the drip tray/drain if plumbed in) when the solenoid valve is open.
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Postby fransg on Fri Mar 15, 2013 5:13 am

This is what it looks like. You can see the gradual buildup of pressure to 6 bar, then briefly to 9 bar, a swift drop after clicking back to 6 bar, a brief focus on the finished shot and a moment looking at the crema from the top.

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Postby pizzaman383 on Fri Mar 15, 2013 8:51 pm

I wanted to try pressure profiling with an OPV on my VBM. So, I installed a separate, second OPV which I could easily adjust from the top of the machine (with the drip tray removed). It was fairly easy by changing fittings, rerouting tubing, etc. like this mod. Mine doesn't have the solenoid and switch because I started by experimenting.

I thought that I would be able to put a big hand-wheel on the OPV so I could reduce the pressure throughout the shot. Well, it did work and I was able to adjust the OPV. With the OPV I used it was about one revolution per bar so it was too much distance to easily move. Also the thing added vibration sources that made the machine more noisy.

After a few weeks of playing with it I ended up just setting the OPV to 10 bar and left it. I didn't find it changed the taste of my espresso enough to stick with it. I would have needed to refine the installation to make it easier to use and to be quieter but I didn't think it was worth the effort.
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