OPV Adjustment for the Gaggia Classic
1. You will need a pressure gauge that has been modified to fit the bottom of the standard domestic Gaggia portafilter. (fig a)
This assembly cost me less than £10 to construct and the parts were readily available.
2. Prime and warm up your machine to the normal operating temperature (At least 20 mins).
3. Youíll notice that thereís no basket in the portafilter above, false pressure readings will be given if you leave it in there. Fill the pressure gauge with water from your machine before attaching it to the head. This serves to eliminate the chances of air being trap in the portafilter and primes your machine for the first test.
4. Switch the pump on. As the pressure rises open the steam valve a little, this will hopefully allow any remaining air out of the system. Once you have a steady stream of water from the steam wand close it and allow the pressure to build until it settles.
If youíve never adjusted your OPV before youíll probably looking at around 14 bar of pressure. These machines are shipped at this pressure for use with pods so if you do use pods donít touch a thing. Make a note of your reading and switch off the pump.
5. SWITCH THE POWER OFF AT THE WALL AND REMOVE THE PLUG FOR ABSOLUTE PEACE OF MIND.
6. Remove the two screws from the rear of the top plate and lift away. There is an earth wire attached to the cover, remove it but do not forget to replace it on reassembly.
7. Itís hot in there, be careful. Part of the reason for having the machine warm is that it comes apart a lot easier. Locate the OPV (fig b)
(fig b) OPV valve
Remove the pipe and put it to one side out of the way. (fig c)[/CENTER]
(fig c) OPV pipe removed
Using a ratchet wrench, extension and 17mm head remove the top of the OPV. I have specified the tool because I have read of people attempting this with spanners or adjustable spanner even pliers. This is a really bad idea. Like I said itís hot and you will inevitable burn yourself. At best a spanner will slip and you may damage something else such as your solenoid.
Once the top of the OPV is removed you will see a small 5mm (3/16) hex head inside. It can be difficult to see sometimes as there will be water on top of it, but trust me itís there. (fig d 1 and 2)
(fig d 1) OPV, 5 mm hex head revealed
Insert a 5mm (3/16) Allen key in the hole and turn it anti clockwise approximately 270į or three quarters of a turn. Reassemble your machine in reverse order. Donít forget that earth wire and re test the pressure.
8. This is known as a static pressure test which means thereís no flow through the portafilter. The pressure you should be aiming for is 10 bar not 9 bar. This is because the difference between a static reading of 9 bar and a dynamic reading i.e. with flow through the head is 1 bar less. Therefore you need to set your machines to 10 bar which will give you 9 bar dynamic.
Here's a video of the gauge in action (at this point it's reading 9 bar instead of 10 bar) http://flic.kr/p/9LQDDk
9. You will need to repeat this a few times to get it right but itís worth it IMHO. I am pulling vastly improved shots with much better crema.
Disclaimer: I can not be held responsible for any damage that may invalidate any warranty. You should only attempt this adjustment if you know what you are doing and have the right tools to do it. If you do not feel in any way confident then leave it alone.