Espresso brew pressure profiling: dual OPV on the Rocket Giotto

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

He has made me a temperature probe to fit in a portafilter basket:

 (I will post more about this nifty device soon)

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:

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:

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

 An image of the spring inside this OPV:

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.

Peter made the OPV a little deeper:

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:

 I liked the idea very much so Peter set forth:

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:

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.

 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:

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).

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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